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Versions: (draft-pinkerton-rddp-security) 00 01 02 03 04 05 06 07 08 09 10 RFC 5042

Internet Draft                            James Pinkerton
draft-ietf-rddp-security-03.txt             Microsoft Corporation
Category: Standards Track                 Ellen Deleganes
Expires: February, 2005                     Intel Corporation
                                          Sara Bitan
                                            Microsoft Corporation
                                          August 2004



                           DDP/RDMAP Security

1  Status of this Memo

   This document is an Internet-Draft and is in full conformance
   with all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet-Drafts
   as reference material or to cite them other than as "work in
   progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

2  Abstract

   This document analyzes security issues around implementation and
   use of the Direct Data Placement Protocol(DDP) and Remote Direct
   Memory Access Protocol (RDMAP). It first defines an architectural
   model for an RDMA Network Interface Card (RNIC), which can
   implement DDP or RDMAP and DDP. The document reviews various
   attacks against the resources defined in the architectural model
   and the countermeasures that can be used to protect the system.
   Attacks are grouped into spoofing, tampering, information
   disclosure, denial of service, and elevation of privilege.
   Finally, the document concludes with a summary of security
   services for DDP and RDMAP, such as IPSec.







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   Table of Contents

   1    Status of this Memo.........................................1
   2    Abstract....................................................1
   2.1  Issues......................................................3
   2.2  Revision History............................................4
   2.2.1  Changes from -02 to -03 version............................4
   2.2.2  Changes from the -01 to the -02 version....................4
   2.2.3  Changes from the -00 to -01 version........................4
   3    Introduction................................................6
   4    Architectural Model.........................................8
   4.1  Components..................................................9
   4.2  Resources..................................................11
   4.2.1  Stream Context Memory.....................................11
   4.2.2  Data Buffers..............................................11
   4.2.3  Page Translation Tables...................................11
   4.2.4  STag Namespace............................................12
   4.2.5  Completion Queues.........................................12
   4.2.6  Asynchronous Event Queue..................................12
   4.2.7  RDMA Read Request Queue...................................13
   4.2.8  RNIC Interactions.........................................13
   4.2.8.1   Privileged Control Interface Semantics................13
   4.2.8.2   Non-Privileged Data Interface Semantics...............13
   4.2.8.3   Privileged Data Interface Semantics...................14
   4.2.9  Initialization of RNIC Data Structures for Data Transfer..14
   4.2.10  RNIC Data Transfer Interactions.........................15
   5    Trust and Resource Sharing.................................17
   6    Attacker Capabilities......................................18
   7    Attacks and Countermeasures................................19
   7.1  Tools for Countermeasures..................................19
   7.1.1  Protection Domain (PD)....................................19
   7.1.2  Limiting STag Scope.......................................20
   7.1.3  Access Rights.............................................21
   7.1.4  Limiting the Scope of the Completion Queue................21
   7.1.5  Limiting the Scope of an Error............................21
   7.2  Spoofing...................................................21
   7.2.1  Impersonation.............................................22
   7.2.2  Stream Hijacking..........................................22
   7.2.3  Man in the Middle Attack..................................22
   7.2.4  Using an STag on a Different Stream.......................23
   7.3  Tampering..................................................24
   7.3.1  Buffer Overrun - RDMA Write or Read Response..............24
   7.3.2  Modifying a Buffer After Indication.......................25
   7.3.3  Multiple STags to access the same buffer..................25
   7.3.4  Network based modification of buffer content..............25
   7.4  Information Disclosure.....................................26
   7.4.1  Probing memory outside of the buffer bounds...............26
   7.4.2  Using RDMA Read to Access Stale Data......................26
   7.4.3  Accessing a Buffer After the Transfer.....................26
   7.4.4  Accessing Unintended Data With a Valid STag...............26
   7.4.5  RDMA Read into an RDMA Write Buffer.......................27
   7.4.6  Using Multiple STags Which Alias to the Same Buffer.......27


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   7.4.7  Remote Node Loading Firmware onto the RNIC................28
   7.4.8  Controlling Access to PTT & STag Mapping..................28
   7.4.9  Network based eavesdropping...............................28
   7.5  Denial of Service (DOS)....................................29
   7.5.1  RNIC Resource Consumption.................................29
   7.5.2  Resource Consumption By Active Applications...............30
   7.5.2.1   Multiple Streams Sharing Receive Buffers..............30
   7.5.2.2   Local Peer Attacking a Shared CQ......................31
   7.5.2.3   Remote Peer Attacking a Shared CQ.....................32
   7.5.2.4   Attacking the RDMA Read Request Queue.................35
   7.5.3  Resource Consumption by Idle Applications.................36
   7.5.4  Exercise of non-optimal code paths........................36
   7.5.5  Remote Invalidate an STag Shared on Multiple Streams......37
   7.6  Elevation of Privilege.....................................37
   8    Security Services for RDMA and DDP.........................38
   8.1  Introduction to Security Options...........................38
   8.1.1  Introduction to IPsec.....................................38
   8.1.2  Introduction to SSL Limitations on RDMAP..................40
   8.1.3  Applications Which Provide Security.......................40
   8.2  Requirements for IPsec Encapsulation of DDP................40
   9    Security considerations....................................42
   10   References.................................................43
   10.1   Normative References......................................43
   10.2   Informative References....................................43
   11   Appendix A: Implementing Client/Server Protocols...........44
   12   Appendix B: Summary Table of Attacks.......................47
   13   Appendix C: Partial Trust Taxonomy.........................48
   14   AuthorÆs Addresses.........................................50
   15   Acknowledgments............................................51
   16   Full Copyright Statement...................................52


   Table of Figures

   Figure 1 - RDMA Security Model....................................9



2.1  Issues

   This section is temporary and will go away when all issues have
   been resolved.

   Issue: Guidance for application protocols like NFS which
   implement security <TBD>.........................................40









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2.2  Revision History

2.2.1  Changes from -02 to -03 version

       *   ID changed from Informational to Standards Track. This
           caused previous RECOMMENDATIONS to be categorized into
           the categories of MUST, SHOULD, MAY, RECOMMENDED, and in
           one case, "recommended".

       *   Completed Appendix B: Summary of Attacks to provide a
           summary of implementation requirements for applications
           using RDDP and for RNICs in Appendix B: Summary of
           Attacks.

       *   Modified intro to better explain when concept of Partial
           Mutual Trust is useful.

       *   Misc minor changes from Tom Talpey's extensive review,
           including:

           *   Send Queue/Receive Queue formally defined/used.

           *   RI is gone, now use RNIC interface, RNIC, and Remote
               Invalidate.

           *   Clarified attackers capabilities.

           *   In many cases replaced "session" with "Stream".

           *   Added definitions for equation variables in section
               7.5.2.3.

       *   Changed section 8.2 to normative xref to IPS Security,
           plus comment on the value of end-to-end IPsec.

       *   Added clarifying example on STag invalidation (e.g. One-
           Shot STag discussion).

       *   Added clarifying text on why SSL is a bad idea.

       *   Normative statement on mitigation for Shared RQ.

2.2.2  Changes from the -01 to the -02 version

   Minimal - some typos, deleted some text previously marked for
   deletion.

2.2.3  Changes from the -00 to -01 version

       *   Added two pages to the architectural model to describe
           the Asynchronous Event Queue, and the types of



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           interactions that can occur between the RNIC and the
           modules above it.

       *   Addressed Mike Krauses comments submitted on 12/8/2003

       *   Moved "Trust Models" from the body of the document to an
           appendix. Removed references to it throughout the
           document (including use of "partial trust". Document now
           assumes Remote Peer is untrusted. Thus the key issue is
           whether local resources are shared, and what the resource
           is.

       *   Misc cleanup throughout the document.

       *   The Summary of Attacks at the end of the document is now
           an Appendix. It also now provides a summary. Cleared
           change bars because became unreadable. Also shortened
           section names for attacks to fit in table.

       *   Added a new concept of "Partial Mutual Trust" between a
           collection of Streams to better characterize a set of
           attacks in a client/server environment.

       *   Filled in Security Services for RDMA and DDP section
           (almost all is new, except IPsec overview).

       *   Globally tried to change "connection" to "Stream". In
           some cases it can be either a connection or stream.


























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3  Introduction

   RDMA enables new levels of flexibility when communicating between
   two parties compared to current conventional networking practice
   (e.g. a stream-based model or datagram model). This flexibility
   brings new security issues that must be carefully understood when
   designing application protocols utilizing RDMA and when
   implementing RDMA-aware NICs (RNICs). Note that for the purposes
   of this security analysis, an RNIC may implement RDMAP and DDP,
   or just DDP.

   The specification first develops an architectural model that is
   relevant for the security analysis - it details components,
   resources, and system properties that may be attacked in Section
   4.

   It then defines what resources a ULP may share locally across
   Streams and what resources the ULP may share with the Remote Peer
   across Streams in Section 5. Intentional sharing of resources
   between multiple Streams may imply some level of trust between
   the Streams. However, some types of resource sharing have
   unmitigated security attacks which would mandate not sharing a
   specific type of resource unless there is some level of trust
   between the Streams sharing resources. Partial Mutual Trust is
   defined to address this concept:

        Partial Mutual Trust - a collection of RDMAP/DDP Streams,
        which represent the local and remote end points of the
        Stream, are willing to assume that the Streams from the
        collection will not perform malicious attacks against any of
        the Streams in the collection. Applications have explicit
        control of which collection of endpoints is in the
        collection through tools discussed in Section 7.1 Tools for
        Countermeasures on page 19.

   An untrusted peer relationship is appropriate when an application
   wishes to ensure that it will be robust and uncompromised even in
   the face of a deliberate attack by its peer. For example, a
   single application that concurrently supports multiple unrelated
   Streams (e.g. a server) would presumably treat each of its peers
   as an untrusted peer. For a collection of Streams which share
   Partial Mutual Trust, the assumption is that any Stream not in
   the collection is untrusted. For the untrusted peer, a brief list
   of capabilities is enumerated in Section 6.

   The rest of the specification is focused on analyzing attacks.
   First, the tools for mitigating attacks are listed (Section 7.1),
   and then a series of attacks on components, resources, or system
   properties is enumerated in the rest of Section 7. For each
   attack, possible countermeasures are reviewed. If all recommended
   mitigations are in place the implemented usage models, the



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   RDMAP/DDP protocol can be shown to not expose any new security
   vulnerabilities.

   Applications within a host are divided into two categories -
   Privileged and Non-Privileged. Both application types can send
   and receive data and request resources. The key differences
   between the two are:

        The Privileged Application is trusted by the system to not
        maliciously attack the operating environment, but it is not
        trusted to optimize resource allocation globally. For
        example, the Privileged Application could be a kernel
        application, thus the kernel presumably has in some way
        vetted the application before allowing it to execute.

        A Non-Privileged ApplicationÆs capabilities are a logical
        sub-set of the Privileged ApplicationÆs. It is assumed by
        the local system that a Non-Privileged Application is
        untrusted. All Non-Privileged Application interactions with
        the RNIC Engine that could affect other applications need to
        be done through a trusted intermediary that can verify the
        Non-Privileged Application requests.
































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4  Architectural Model

   This section describes an RDMA architectural reference model that
   is used as security issues are examined. It introduces the
   components of the model, the resources that can be attacked, the
   types of interactions possible between components and resources,
   and the system properties which must be preserved.

   Figure 1 shows the components comprising the architecture and the
   interfaces where potential security attacks could be launched.
   External attacks can be injected into the system from an
   application that sits above the RNIC Interface or from the
   network.

   The intent here is to describe high level components and
   capabilities which affect threat analysis, and not focus on
   specific implementation options. Also note that the architectural
   model is an abstraction, and an actual implementation may choose
   to subdivide its components along different boundary lines than
   defined here. For example, the Privileged Resource Manager may be
   partially or completely encapsulated in the Privileged
   Application. Regardless, it is expected that the security
   analysis of the potential threats and countermeasures still
   apply.






























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          +-------------+
          |  Privileged |
          |  Resource   |
 Admin<-+>|  Manager    |     App Control Interface
        | |             |<------+-------------------+
        | +-------------+       |                   |
        |       ^               v                   v
        |       |         +-------------+   +-----------------+
        |---------------->| Privileged  |   |  Non-Privileged |
                |         | Application |   |  Application    |
                |         +-------------+   +-----------------+
                |               ^                   ^
                |Privileged     |Privileged         |Non-Privileged
                |Control        |Data               |Data
                |Interface      |Interface          |Interface
RNIC            |               |                   |
Interface       v               v                   v
=================================================================

              +--------------------------------------+
              |                                      |
              |               RNIC Engine            | <-- Firmware
              |                                      |
              +--------------------------------------+
                                ^
                                |
                                v
                             Internet

                     Figure 1 - RDMA Security Model

4.1  Components

   The components shown in Figure 1 - RDMA Security Model are:

       *   RNIC Engine (RNIC) - the component that implements the
           RDMA protocol and/or DDP protocol.

       *   Privileged Resource Manager - the component responsible
           for managing and allocating resources associated with the
           RNIC Engine. The Resource Manager does not send or
           receive data. Note that whether the Resource Manager is
           an independent component, part of the RNIC, or part of
           the application is implementation dependent. If a
           specific implementation does not wish to address security
           issues resolved by the Resource Manager, there may in
           fact be no resource manager at all.

       *   Privileged Application - See Section 3 Introduction for a
           definition of Privileged Application. The local host
           infrastructure can enable the Privileged Application to


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           map a data buffer directly from the RNIC Engine to the
           host through the RNIC Interface, but it does not allow
           the Privileged Application to directly consume RNIC
           Engine resources.

       *   Non-Privileged Application - See Section 3 Introduction
           for a definition of Non-Privileged Application. All Non-
           Privileged Application interactions with the RNIC Engine
           that could affect other applications MUST be done using
           the Privileged Resource Manager as a proxy.

   A design goal of the DDP and RDMAP protocols is to allow, under
   constrained conditions, Non-Privileged applications to send and
   receive data directly to/from the RDMA Engine without Privileged
   Resource Manager intervention - while ensuring that the host
   remains secure. Thus, one of the primary goals of this paper is
   to analyze this usage model for the enforcement that is required
   in the RNIC Engine to ensure the system remains secure.

   The host interfaces that could be exercised include:

       *   Privileged Control Interface - A Privileged Resource
           Manager uses the RNIC Interface to allocate and manage
           RNIC Engine resources, control the state within the RNIC
           Engine, and monitor various events from the RNIC Engine.
           It also uses this interface to act as a proxy for some
           operations that a Non-Privileged Application may require
           (after performing appropriate countermeasures).

       *   Application Control Interface - An application uses this
           interface to the Privileged Resource Manager to allocate
           RNIC Engine resources. The Privileged Resource Manager
           implements countermeasures to ensure that if the Non-
           Privileged Application launches an attack it can prevent
           the attack from affecting other applications.

       *   Non-Privileged Data Transfer Interface - A Non-Privileged
           Application uses this interface to initiate and to check
           the status of data transfer operations.

       *   Privileged Data Transfer Interface - A superset of the
           functionality provided by the Non-Privileged Data
           Transfer Interface. The application is allowed to
           directly manipulate RNIC Engine mapping resources to map
           an STag to an application data buffer.

       *   Figure 1 also shows the ability to load new firmware in
           the RNIC Engine. Not all RNICs will support this, but it
           is shown for completeness and is also reviewed under
           potential attacks.




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   If Internet control messages, such as ICMP, ARP, RIPv4, etc. are
   processed by the RNIC Engine, the threat analyses for those
   protocols is also applicable, but outside the scope of this
   paper.

4.2  Resources

   This section describes the primary resources in the RNIC Engine
   that could be affected if under attack. For RDMAP, all of the
   defined resources apply. For DDP, all of the resources except the
   RDMA Read Queue apply.

4.2.1  Stream Context Memory

   The state information for each Stream is maintained in memory,
   which could be located in a number of places - on the NIC, inside
   RAM attached to the NIC, in host memory, or in any combination of
   the three, depending on the implementation.

   Stream Context Memory includes state associated with Data
   Buffers. For Tagged Buffers, this includes how STag names, Data
   Buffers, and Page Translation Tables inter-relate. It also
   includes the list of Untagged Data Buffers posted for reception
   of Untagged Messages (commonly called the Receive Queue), and a
   list of operations to perform to send data (commonly called the
   Send Queue).

4.2.2  Data Buffers

   There are two different ways to expose a data buffer; a buffer
   can be exposed for receiving RDMAP Send Type Messages (a.k.a. DDP
   Untagged Messages) on DDP Queue zero or the buffer can be exposed
   for remote access through STags (a.k.a. DDP Tagged Messages).
   This distinction is important because the attacks and the
   countermeasures used to protect against the attack are different
   depending on the method for exposing the buffer to the network.

   For the purposes of the security discussion, a single logical
   Data Buffer is exposed with a single STag. Actual implementations
   may support scatter/gather capabilities to enable multiple
   physical data buffers to be accessed with a single STag, but from
   a threat analysis perspective it is assumed that a single STag
   enables access to a single logical Data Buffer.

   In any event, it is the responsibility of the RNIC to ensure that
   no STag can be created that exposes memory that the consumer had
   no authority to expose.

4.2.3  Page Translation Tables

   Page Translation Tables are the structures used by the RNIC to be
   able to access application memory for data transfer operations.


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   Even though these structures are called "Page" Translation
   Tables, they may not reference a page at all - conceptually they
   are used to map an application address space representation of a
   buffer to the physical addresses that are used by the RNIC Engine
   to move data. If on a specific system a mapping is not used, then
   a subset of the attacks examined may be appropriate. Note that
   the Page Translation Table may or may not be a shared resource.

4.2.4  STag Namespace

   The DDP specification defines a 32-bit namespace for the STag.
   Implementations may vary in terms of the actual number of STags
   that are supported. In any case, this is a bounded resource that
   can come under attack. Depending upon STag namespace allocation
   algorithms, the actual name space to attack may be significantly
   less than 2^32.

4.2.5  Completion Queues

   Completion Queues are used in this specification to conceptually
   represent how the RNIC Engine notifies the Application about the
   completion of the transmission of data, or the completion of the
   reception of data through the Data Transfer Interface. Because
   there could be many transmissions or receptions in flight at any
   one time, completions are modeled as a queue rather than a single
   event. An implementation may also use the Completion Queue to
   notify the application of other activities, for example, the
   completion of a mapping of an STag to a specific application
   buffer. Completion Queues may be shared by a group of Streams, or
   may be designated to handle a specific Stream's traffic.

   Some implementations may allow this queue to be manipulated
   directly by both Non-Privileged and Privileged applications.

4.2.6  Asynchronous Event Queue

   The Asynchronous Event Queue is a queue from the RNIC to the
   Privileged Resource Manager of bounded size. It is used by the
   RNIC to notify the host of various events which might require
   management action, including protocol violations, Stream state
   changes, local operation errors, low water marks on receive
   queues, and possibly other events.

   The Asynchronous Event Queue is a resource that can be attacked
   because Remote or Local Peers can cause events to occur which
   have the potential of overflowing the queue.

   Note that an implementation is at liberty to implement the
   functions of the Asynchronous Event Queue in a variety of ways,
   including multiple queues or even simple callbacks. All
   vulnerabilities identified are intended to apply regardless of



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   the implementation of the Asynchronous Event Queue. For example,
   a callback function is simply a very short queue.

4.2.7  RDMA Read Request Queue

   The RDMA Read Request Queue is the memory that holds state
   information for one or more RDMA Read Request Messages that have
   arrived, but for which the RDMA Read Response Messages have not
   yet been completely sent. Because potentially more than one RDMA
   Read Request can be outstanding at one time, the memory is
   modeled as a queue of bounded size.

4.2.8  RNIC Interactions

   With RNIC resources and interfaces defined, it is now possible to
   examine the interactions supported by the generic RNIC functional
   interfaces through each of the 3 interfaces - Privileged Control
   Interface, Privileged Data Interface, and Non-Privileged Data
   Interface.

4.2.8.1  Privileged Control Interface Semantics

   Generically, the Privileged Control Interface controls the RNICÆs
   allocation, deallocation, and initialization of RNIC global
   resources. This includes allocation and deallocation of Stream
   Context Memory, Page Translation Tables, STag names, Completion
   Queues, RDMA Read Request Queues, and Asynchronous Event Queues.

   The Privileged Control Interface is also typically used for
   managing Non-Privileged Application resources for the Non-
   Privileged Application (and possibly for the Privileged
   Application as well). This includes initialization and removal of
   Page Translation Table resources, and managing RNIC events
   (possibly managing all events for the Asynchronous Event Queue).

4.2.8.2  Non-Privileged Data Interface Semantics

   The Non-Privileged Data Interface enables data transfer (transmit
   and receive) but does not allow initialization of the Page
   Translation Table resources. However, once the Page Translation
   Table resources have been initialized, the interface may enable a
   specific STag mapping to be enabled and disabled by directly
   communicating with the RNIC, or create an STag mapping for a
   buffer that has been previously initialized in the RNIC.

   For RDMAP, transmitting data means sending RDMAP Send Type
   Messages, RDMA Read Requests, and RDMA Writes. For data
   reception, for RDMAP it can receive Send Type Messages into
   buffers that have been posted on the Receive Queue or Shared
   Receive Queue. It can also receive RDMA Write and RDMA Read
   Response Messages into buffers that have previously been exposed
   for external write access through advertisement of an STag.


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   For DDP, transmitting data means sending DDP Tagged or Untagged
   Messages. For data reception, for DDP it can receive Untagged
   Messages into buffers that have been posted on the Receive Queue
   or Shared Receive Queue. It can also receive Tagged DDP Messages
   into buffers that have previously been exposed for external write
   access through advertisement of an STag.

   Completion of data transmission or reception generally entails
   informing the application of the completed work by placing
   completion information on the Completion Queue.

4.2.8.3  Privileged Data Interface Semantics

   The Privileged Data Interface semantics are a superset of the
   Non-Privileged Data Transfer semantics. The interface can do
   everything defined in the prior section, as well as
   create/destroy buffer to STag mappings directly. This generally
   entails initialization or clearing of Page Translation Table
   state in the RNIC.

4.2.9  Initialization of RNIC Data Structures for Data Transfer

   Initialization of the mapping between an STag and a Data Buffer
   can be viewed in the abstract as two separate opertions:

       a.  Initialization of the allocated Page Translation Table
           entries with the location of the Data Buffer, and

       b.  Initialization of a mapping from an allocated STag name
           to a set of Page Translation Table entry(s) or partial-
           entries.

   Note that an implementation may not have a Page Translation Table
   (i.e. it may support a direct mapping between an STag and a Data
   Buffer). In this case threats and mitigations associated with the
   Page Translation Table are not relevant.

   Initialization of the contents of the Page Translation Table can
   be done by either the Privileged Application or by the Privileged
   Resource Manager as a proxy for the Non-Privileged Application.
   By definition the Non-Privileged Application is not trusted to
   directly manipulate the Page Translation Table. In general the
   concern is that the Non-Privileged application may try to
   maliciously initialize the Page Translation Table to access a
   buffer for which it does not have permission.

   The exact resource allocation algorithm for the Page Translation
   Table is outside the scope of this specification. It may be
   allocated for a specific Data Buffer, or be allocated as a pooled
   resource to be consumed by potentially multiple Data Buffers, or
   be managed in some other way. This paper attempts to abstract
   implementation dependent issues, and focus on higher level


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   security issues such as resource starvation and sharing of
   resources between Streams.

   The next issue is how an STag name is associated with a Data
   Buffer. For the case of an Untagged Data Buffer, there is no wire
   visible mapping between an STag and the Data Buffer. Note that
   there may, in fact, be an STag which represents the buffer.
   However, because the STag by definition is not visible on the
   wire, this is a local host specific issue which should be
   analyzed in the context of local host implementation specific
   security analysis, and thus is outside the scope of this paper.

   For a Tagged Data Buffer, either the Privileged Application, the
   Non-Privileged Application, or the Privileged Resource Manager
   acting on behalf of the Non-Privileged Resource Manager may
   initialize a mapping from an STag to a Page Translation Table, or
   may have the ability to simply enable/disable an existing STag to
   Page Translation Table mapping. There may also be multiple STag
   names which map to a specific group of Page Translation Table
   entries (or sub-entries). Specific security issues with this
   level of flexibility are examined in Section 7.3.3 Multiple STags
   to access the same buffer on page 25.

   There are a variety of implementation options for initialization
   of Page Translation Table entries and mapping an STag to a group
   of Page Translation Table entries which have security
   repercussions. This includes support for separation of Mapping an
   STag verses mapping a set of Page Translation Table entries, and
   support for Applications directly manipulating STag to Page
   Translation Table entry mappings (verses requiring access through
   the Privileged Resource Manager).

4.2.10 RNIC Data Transfer Interactions

   RNIC Data Transfer operations can be subdivided into send
   operations and receive operations.

   For send operations, there is typically a queue that enables the
   Application to post multiple operations to send data (referred to
   as the Send Queue). Depending upon the implementation, Data
   Buffers used in the operations may or may not have Page
   Translation Table entries associated with them, and may or may
   not have STags associated with them. Because this is a local host
   specific implementation issue rather than a protocol issue, the
   security analysis of threats and mitigations is left to the host
   implementation.

   Receive operations are different for Tagged Data Buffers verses
   Untagged Data Buffers. If more than one Untagged Data Buffer can
   be posted by the Application, the DDP specification requires that
   they be consumed in sequential order. Thus the most general
   implementation is that there is a sequential queue of receive


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   Untagged Data Buffers (Receive Queue). Some implementations may
   also support sharing of the sequential queue between multiple
   Streams. In this case defining "sequential" becomes non-trivial -
   in general the buffers for a single stream are consumed from the
   queue in the order that they were placed on the queue, but there
   is no order guarantee between streams.

   For receive Tagged Data Buffers, at some time prior to data
   transfer, the mapping of the STag to specific Page Translation
   Table entries (if present) and the mapping from the Page
   Translation Table entries to the Data Buffer must have been
   initialized (see the prior section for interaction details).










































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5  Trust and Resource Sharing

   It is assumed that in general the Local and Remote Peer are
   untrusted, and thus attacks by either should have mitigations in
   place.

   A separate, but related issue is resource sharing between
   multiple streams. If local resources are not shared, the
   resources are dedicated on a per Stream basis. Resources are
   defined in Section 4.2 - Resources on page 10. The advantage of
   not sharing resources between Streams is that it reduces the
   types of attacks that are possible. The disadvantage is that
   applications might run out of resources.

   It is assumed in this paper that the component that implements
   the mechanism to control sharing of the RNIC Engine resources is
   the Privileged Resource Manager. The RNIC Engine exposes its
   resources through the RNIC Interface to the Privileged Resource
   Manager. All Privileged and Non-Privileged applications request
   resources from the Resource Manager. The Resource Manager
   implements resource management policies to ensure fair access to
   resources. The Resource Manager should be designed to take into
   account security attacks detailed in this specification. Note
   that for some systems the Privileged Resource Manager may be
   implemented within the Privileged Application.

   The sharing of resources across Streams should be under the
   control of the application, both in terms of the trust model the
   application wishes to operate under, as well as the level of
   resource sharing the application wishes to give Local Peer
   processes. For more discussion on types of trust models which
   combine partial trust and sharing of resources, see Appendix C:
   Partial Trust Taxonomy on page 48.





















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6  Attacker Capabilities

   An attackerÆs capabilities delimit the types of attacks that
   attacker is able to launch. RDMAP and DDP require that the
   initial LLP Stream (and connection) be set up prior to
   transferring RDMAP/DDP Messages. Attackers with send only
   capabilities must first guess the current LLP Stream parameters
   before they can attack RNIC resources (e.g. TCP sequence number).
   Attackers with both send and receive capabilities have presumably
   setup a valid LLP Stream, and thus have a wider ability to attack
   RNIC resources.











































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7  Attacks and Countermeasures

   This section describes the attacks that are possible against the
   RDMA system defined in Figure 1 - RDMA Security Model and the
   RNIC Engine resources defined in Section 4.2. The analysis
   includes a detailed description of each attack, what is being
   attacked, and a description of the countermeasures that can be
   taken to thwart the attack.

   Note that connection setup and teardown is presumed to be done in
   stream mode (i.e. no RDMA encapsulation of the payload), so there
   are no new attacks related to connection setup/teardown beyond
   what is already present in the LLP (e.g. TCP or SCTP). Note,
   however, that RDMAP/DDP parameters may be exchanged in stream
   mode, and if they are corrupted by an attacker unintended
   consequences will result. Therefore, any existing mitigations for
   LLP Spoofing, Tampering, Repudiation, Information Disclosure,
   Denial of Service, or Elevation of Privilege continues to apply
   (and is out of scope of this document). Thus the analysis in this
   section focuses on attacks that are present regardless of the LLP
   Stream type.

   The attacks are classified into five categories: Spoofing,
   Tampering, Information Disclosure, Denail of Service (DoS)
   attacks, and Elevation of Privileges. Tampering is any
   modification of the legitimate traffic (machine internal or
   network). Spoofing attack is a special case of tempering; where
   the attacker falsifies an identity of the Remote Peer (identity
   can be an IP address, machine name, ULP level identity etc.).

7.1  Tools for Countermeasures

   The tools described in this section are the primary mechanisms
   that can be used to provide countermeasures to potential attacks.

7.1.1  Protection Domain (PD)

   Protection Domains are associated with two of the resources of
   concern, Stream Context Memory and STags associated with Page
   Translation Table entries and data buffers. Protection Domains
   are used mainly to ensure that an STag can only be used to access
   the associated data buffer through Streams in the same Protection
   Domain as that STag.

   If an implementation chooses to not share resources between
   Streams, it is recommended that each Stream be associated with
   its own, unique Protection Domain. If an implementation chooses
   to allow resource sharing, it is recommended that Protection
   Domain be limited to the number of Streams that have Partial
   Mutual Trust.




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   Note that an application (either Privileged or Non-Privileged)
   can potentially have multiple Protection Domains. This could be
   used, for example, to ensure that multiple clients of a server do
   not have the ability to corrupt each other. The server would
   allocate a Protection Domain per client to ensure that resources
   covered by the Protection Domain could not be used by another
   (untrusted) client.

7.1.2  Limiting STag Scope

   The key to protecting a local data buffer is to limit the scope
   of its STag to the level appropriate for the Streams which share
   Partial Mutual Trust. The scope of the STag can be measured in
   multiple ways.

       *   Number of Connections and/or Streams on which the STag is
           valid. One way to limit the scope of the STag is to limit
           the connections and/or Streams that are allowed to use
           the STag. As noted in the previous section, use of
           Protection Domains appropriately can limit the scope of
           the STag. The analysis presented in this document assumes
           two mechanisms for limiting the scope of Streams for
           which the STag is valid:

           *   Protection Domain scope. The STag is valid if used on
               any Stream within a specific Protection Domain, and
               is invalid if used on any Stream that is not a member
               of the Protection Domain.

           *   Single Stream scope. The STag is valid on a single
               Stream, regardless of what the Stream association is
               to a Protection Domain. If used on any other Stream,
               it is invalid.

       *   Limit the time an STag is valid. By Invalidating an
           Advertised STag (e.g., revoking remote access to the
           buffers described by an STag when done with the
           transfer), an entire class of attacks can be eliminated.

       *   Limit the buffer the STag can reference. Limiting the
           scope of an STag access to *just* the intended
           application buffers to be exposed is critical to prevent
           certain forms of attacks.

       *   Allocating and/or advertising STag numbers in an
           unpredictable way. If STags are allocated/advertised
           using an algorithm which makes it hard for the attacker
           to guess which STag(s) are currently in use, it makes it
           more difficult for an attacker to guess the correct
           value. As stated in the RDMAP specification [RDMAP], an
           invalid STag will cause the RDMAP Stream to be
           terminated. For the case of [DDP], at a minimum it must


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           signal an error to the ULP, and commonly this will cause
           the DDP stream to be terminated.

7.1.3  Access Rights

   Access Rights associated with a specific Advertised STag or
   RDMAP/DDP Stream provide another mechanism for applications to
   limit the attack capabilities of the Remote Peer. The Local Peer
   can control whether a data buffer is exposed for local only, or
   local and remote access, and assign specific access privileges
   (read, write, read and write) on a per stream basis.

   For DDP, when an STag is advertised, the Remote Peer is
   presumably given write access rights to the data (otherwise there
   was not much point to the advertisement). For RDMAP, when an
   application advertises an STag, it can enable write-only, read-
   only, or both write and read access rights.

   Similarly, some applications may wish to provide a single buffer
   with different access rights on a per-Stream or per-Stream basis.
   For example, some Streams may have read-only access, some may
   have remote read and write access, while on other Streams only
   the Local Peer is allowed access.

7.1.4  Limiting the Scope of the Completion Queue

   Completions associated with sending and receiving data, or
   setting up buffers for sending and receiving data, could be
   accumulated in a shared Completion Queue for a group of RDMAP/DDP
   Streams, or a specific RDMAP/DDP Stream could have a dedicated
   Completion Queue. Limiting Completion Queue association to one,
   or a small number of RDMAP/DDP Streams can prevent several forms
   of Denial of Service attacks.

7.1.5  Limiting the Scope of an Error

   To prevent a variety of attacks, it is important that an
   RDMAP/DDP implementation be robust in the face of errors. If an
   error on a specific Stream can cause other unrelated Streams to
   fail, then a broad class of attacks are enabled against the
   implementation.

   For example, an error on a specific RDMAP stream should not cause
   the RNIC to stop processing incoming packets, or corrupt a
   receive queue for an unrelated stream.

7.2  Spoofing

   Spoofing attacks can be launched by the Remote Peer, or by a
   network based attacker. A network based spoofing attack applies
   to all Remote Peers.



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   Because the RDMAP Stream requires an LLP Stream in the
   ESTABLISHED state, certain types of traditional forms of wire
   attacks do not apply -- an end-to-end handshake must have
   occurred to establish the RDMAP Stream. So, the only form of
   spoofing that applies is one when a remote node can both send and
   receive packets. Yet even with this limitation the Stream is
   still exposed to the following spoofing attacks.

7.2.1  Impersonation

   A network based attacker can impersonate a legal RDMA/DDP peer
   (by spoofing a legal IP address), and establish an RDMA/DDP
   Stream with the victim. End to end authentication (i.e. IPsec,
   SSL or ULP authentication) provides protection against this
   attack. For additional information see Section 8, Security
   Services for RDMA and DDP, on page 38.

7.2.2  Stream Hijacking

   Stream hijacking happens when a network based attacker follows
   the Stream establishment phase, and waits until the
   authentication phase (if such a phase exists) is completed
   successfully. He can then spoof the IP address and re-direct the
   Stream from the victim to its own machine. For example, an
   attacker can wait until an iSCSI authentication is completed
   successfully, and hijack the iSCSI Stream.

   The best protection against this form of attack is end-to-end
   integrity protection and authentication, such as IPsec (see
   Section 8, Security Services for RDMA and DDP, on page 38), to
   prevent spoofing. Another option is to provide physical security.
   Discussion of physical security is out of scope for this
   document.

   Because the connection and/or Stream itself is established by the
   LLP, some LLPs are more difficult to hijack than others. Please
   see the relevant LLP documentation on security issues around
   connection and/or Stream hijacking.

7.2.3  Man in the Middle Attack

   If a network based attacker has the ability to delete, inject
   replay, or modify packets which will still be accepted by the LLP
   (e.g., TCP sequence number is correct) then the Stream can be
   exposed to a man in the middle attack. One style of attack is for
   the man-in-the-middle to send Tagged Messages (either RDMAP or
   DDP). If it can discover a buffer that has been exposed for STag
   enabled access, then the man-in-the-middle can use an RDMA Read
   operation to read the contents of the associated data buffer,
   perform an RDMA Write Operation to modify the contents of the
   associated data buffer, or invalidate the STag to disable further
   access to the buffer. The only countermeasure for this form of


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   attack is to either secure the RDMAP/DDP Stream (i.e. integrity
   protect) or attempt to provide physical security to prevent man-
   in-the-middle type attacks.

   The best protection against this form of attack is end-to-end
   integrity protection and authentication, such as IPsec (see
   Section 8 Security Services for RDMA and DDP on page 38), to
   prevent spoofing or tampering. If Stream or session level
   authentication and integrity protection are not used, then a man-
   in-the-middle attack can occur, enabling spoofing and tampering.

   Because the connection/Stream itself is established by the LLP,
   some LLPs are more exposed to man-in-the-middle attack then
   others. Please see the relevant LLP documentation on security
   issues around connection and/or Stream hijacking.

   Another approach is to restrict access to only the local
   subnet/link, and provide some mechanism to limit access, such as
   physical security or 802.1.x. This model is an extremely limited
   deployment scenario, and will not be further examined here.

7.2.4  Using an STag on a Different Stream

   One style of attack from the Remote Peer is for it to attempt to
   use STag values that it is not authorized to use. Note that if
   the Remote Peer sends an invalid STag to the Local Peer, per the
   DDP and RDMAP specifications, the Stream must be torn down. Thus
   the threat exists if a STag has been enabled for Remote Access on
   one Stream and a Remote Peer is able to use it on an unrelated
   Stream. If the attack is successful, the attacker could
   potentially be able to perform either RDMA Read Operations to
   read the contents of the associated data buffer, perform RDMA
   Write Operations to modify the contents of the associated data
   buffer, or to Invalidate the STag to disable further access to
   the buffer.

   An attempt by a Remote Peer to access a buffer with an STag on a
   different Stream in the same Protection Domain may or may not be
   an attack depending on whether resource sharing is intended (i.e.
   whether the Streams shared Partial Mutual Trust or not). For some
   applications using an STag on multiple Streams within the same
   Protection Domain could be desired behavior. For other
   applications attempting to use an STag on a different Stream
   could be considered to be an attack. Since this varies by
   application, an application typically would need to be able to
   control the scope of the STag.

   In the case where an implementation does not share resources
   between Streams (including STags), this attack can be defeated by
   assigning each Stream to a different Protection Domain. Before
   allowing remote access to the buffer, the Protection Domain of
   the Stream where the access attempt was made is matched against


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   the Protection Domain of the STag. If the Protection Domains do
   not match, access to the buffer is denied, an error is generated,
   and the RDMAP Stream associated with the attacking Stream should
   be terminated.

   For implementations that share resources between multiple
   Streams, it may not be practical to separate each Stream into its
   own Protection Domain. In this case, the application can still
   limit the scope of any of the STags to a single Stream (if it is
   enabling it for remote access). If the STag scope has been
   limited to a single Stream, any attempt to use that STag on a
   different Stream will result in an error, and the RDMA Stream
   should be terminated.

   Thus for implementations that do not share STags between Streams,
   each Stream MUST either be in a separate Protection Domain or the
   scope of an STag be limited to a single Stream.

   An additional issue may be unintended sharing of STags (i.e. a
   bug in the application) or a bug in the Remote Peer which causes
   an off-by-one STag to be used. For additional protection, an
   implementation SHOULD allocate STags in such a fashion that it is
   difficult to predict the next allocated STag number. Allocation
   methods which deterministically allocate the next STag should be
   avoided (e.g. a method which always starts with STag equal to one
   and monotonically increases it for each new allocation, or a
   method which always uses the same STag for each operation).

7.3  Tampering

   A Remote Peer or a network based attacker can attempt to tamper
   with the contents of data buffers on a Local Peer that have been
   enabled for remote write access. The types of tampering attacks
   that are possible are outlined in the sections that follow.

7.3.1  Buffer Overrun - RDMA Write or Read Response

   This attack is an attempt by the Remote Peer to perform an RDMA
   Write or RDMA Read Response to memory outside of the valid length
   range of the data buffer enabled for remote write access. This
   attack can occur even when no resources are shared across
   Streams. This issue can also arise if the application has a bug.

   The countermeasure for this type of attack must be in the RNIC
   implementation, using the STag. When the Local Peer specifies to
   the RNIC the base address and the number of bytes in the buffer
   that it wishes to make accessible, the RNIC must ensure that the
   base and bounds check are applied to any access to the buffer
   referenced by the STag before the STag is enabled for access.
   When an RDMA data transfer operation (which includes an STag)
   arrives on a Stream, a base and bounds byte granularity access



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   check must be performed to ensure the operation accesses only
   memory locations within the buffer described by that STag.

   Thus an RNIC implementation MUST ensure that a Remote Peer is not
   able to access memory outside of the buffer specified when the
   STag was enabled for remote access.

7.3.2  Modifying a Buffer After Indication

   This attack can occur if a Remote Peer attempts to modify the
   contents of an STag referenced buffer by performing an RDMA Write
   or an RDMA Read Response after the Remote Peer has indicated to
   the Local Peer that the STag data buffer contents are ready for
   use. This attack can occur even when no resources are shared
   across Streams. Note that a bug in a Remote Peer, or network
   based tampering, could also result in this problem.

   For example, assume the STag referenced buffer contains ULP
   control information as well as ULP payload, and the ULP sequence
   of operation is to first validate the control information and
   then perform operations on the control information. If the Remote
   Peer can perform an additional RDMA Write or RDMA Read Response
   (thus changing the buffer) after the validity checks have been
   completed but before the control data is operated on, the Remote
   Peer could force the ULP down operational paths that were never
   intended.

   The Local Peer can protect itself from this type of attack by
   revoking remote access when the original data transfer has
   completed and before it validates the contents of the buffer. The
   Local Peer can either do this by explicitly revoking remote
   access rights for the STag when the Remote Peer indicates the
   operation has completed, or by checking to make sure the Remote
   Peer Invalidated the STag through the RDMAP Invalidate
   capability, and if it did not, the Local Peer then explicitly
   revokes the STag remote access rights.

   The Local Peer SHOULD follow the above procedure to protect the
   buffer before it validates the contents of the buffer (or uses
   the buffer in any way).

7.3.3  Multiple STags to access the same buffer

   See section 7.4.6 on page 27 for this analysis.

7.3.4  Network based modification of buffer content

   This is actually a man in the middle attack - but only on the
   content of the buffer, as opposed to the man in the middle attack
   presented above, where both the signaling and content can be
   modified. See Section 7.2.3 Man in the Middle Attack on page 22.



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7.4  Information Disclosure

   The main potential source for information disclosure is through a
   local buffer that has been enabled for remote access. If the
   buffer can be probed by a Remote Peer on another Stream, then
   there is potential for information disclosure.

   The potential attacks that could result in unintended information
   disclosure and countermeasures are detailed in the following
   sections.

7.4.1  Probing memory outside of the buffer bounds

   This is essentially the same attack as described in Section
   7.3.1, except an RDMA Read Request is used to mount the attack.
   The same countermeasure applies.

7.4.2  Using RDMA Read to Access Stale Data

   If a buffer is being used for a combination of reads and writes
   (either remote or local), and is exposed to the Remote Peer with
   at least remote read access rights, the Remote Peer may be able
   to examine the contents of the buffer before they are initialized
   with the correct data. In this situation, whatever contents were
   present in the buffer before the buffer is initialized can be
   viewed by the Remote Peer, if the Remote Peer performs an RDMA
   Read.

   Because of this, the Local Peer SHOULD ensure that no stale data
   is contained in the buffer before remote read access rights are
   granted (this can be done by zeroing the contents of the memory,
   for example).

7.4.3  Accessing a Buffer After the Transfer

   If the Remote Peer has remote read access to a buffer, and by
   some mechanism tells the Local Peer that the transfer has been
   completed, but the Local Peer does not disable remote access to
   the buffer before modifying the data, it is possible for the
   Remote Peer to retrieve the new data.

   This is similar to the attack defined in Section 7.3.2 Modifying
   a Buffer After Indicati on page 25. The same countermeasures
   apply. In addition, the Local Peer SHOULD grant remote read
   access rights only for the amount of time needed to retrieve the
   data.

7.4.4  Accessing Unintended Data With a Valid STag

   If the Local Peer enables remote access to a buffer using an STag
   that references the entire buffer, but intends only a portion of



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   the buffer to be accessed, it is possible for the Remote Peer to
   access the other parts of the buffer anyway.

   To prevent this attack, the Local Peer MUST set the base and
   bounds of the buffer when the STag is initialized to expose only
   the data to be retrieved.

7.4.5  RDMA Read into an RDMA Write Buffer

   One form of disclosure can occur if the access rights on the
   buffer enabled remote read, when only remote write access was
   intended. If the buffer contained application data, or data from
   a transfer on an unrelated Stream, the Remote Peer could retrieve
   the data through an RDMA Read operation.

   The most obvious countermeasure for this attack is to not grant
   remote read access if the buffer is intended to be write-only.
   Then the Remote Peer would not be able to retrieve data
   associated with the buffer. An attempt to do so would result in
   an error and the RDMAP Stream associated with the Stream would be
   terminated.

   Thus if an application only intends a buffer to be exposed for
   remote write access, it MUST set the access rights to the buffer
   to only enable remote write access.

7.4.6  Using Multiple STags Which Alias to the Same Buffer

   Multiple STags which alias to the same buffer at the same time
   can result in unintentional information disclosure if the STags
   are used by different, mutually untrusted, Remote Peers. This
   model applies specifically to client/server communication, where
   the server is communicating with multiple clients, each of which
   do not mutually trust each other.

   If only read access is enabled, then the Local Peer has complete
   control over information disclosure. Thus a server which intended
   to expose the same data (i.e. buffer) to multiple clients by
   using multiple STags to the same buffer creates no new security
   issues beyond what has already been described in this document.
   Note that if the server did not intend to expose the same data to
   the clients, it should use separate buffers for each client (and
   separate STags).

   When one STag has remote read access enabled and a different STag
   has remote write access enabled to the same buffer, it is
   possible for one Remote Peer to view the contents that have been
   written by another Remote Peer.

   If both STags have remote write access enabled and the two Remote
   Peers do not mutually trust each other, it is possible for one



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   Remote Peer to overwrite the contents that have been written by
   the other Remote Peer.

   Thus multiple Remote Peers which do not share Partial Mutual
   Trust MUST NOT be granted write access to the same buffer through
   different STags. A buffer should be exposed to only one untrusted
   Remote Peer at a time to ensure that no information disclosure or
   information tampering occurs between peers.

7.4.7  Remote Node Loading Firmware onto the RNIC

   If the Remote Peer can cause firmware to be loaded onto the RNIC,
   there is an opportunity for information disclosure. See Elevation
   of Privilege in Section 7.6 for this analysis.

7.4.8  Controlling Access to PTT & STag Mapping

   If a Non-Privileged application is able to directly manipulate
   the RNIC Page Translation Tables (which translate from an STag to
   a host address), it is possible that the Non-Privileged
   application could point the Page Translation Table at an
   unrelated applicationÆs buffers and thereby be able to gain
   access to information in the unrelated application.

   As discussed in Section 4 Architectural Model on page 8,
   introduction of a Privileged Resource Manager to arbitrate the
   mapping requests is an effective countermeasure. This enables the
   Privileged Resource Manager to ensure an application can only
   initialize the Page Translation Table (PTT)to point to its own
   buffers.

   Thus if Non-Privileged applications are supported, the Privileged
   Resource Manager MUST verify that the Non-Privileged application
   has the right to access a specific Data Buffer before allowing an
   STag for which the application has access rights to be associated
   with a specific Data Buffer. This can be done when the Page
   Translation Table is initialized to access the Data Buffer or
   when the STag is initialized to point to a group of Page
   Translation Table entries, or both.

7.4.9  Network based eavesdropping

   An attacker that is able to eavesdrop on the network can read the
   content of all read and write access to the peerÆs buffers. To
   prevent information disclosure, the read/written data must be
   encrypted. See also Section 7.2.3 Man in the Middle Attack on
   page 22. The encryption can be done either by the ULP, or by a
   protocol that provides security services to the LLP (e.g. IPsec
   or SSL). Refer to section 8 for discussion of security services
   for DDP/RDMA.




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7.5  Denial of Service (DOS)

   A DOS attack is one of the primary security risks of RDMAP. This
   is because RNIC resources are valuable and scarce, and many
   application environments require communication with untrusted
   Remote Peers. If the remote application can be authenticated or
   encrypted, clearly, the DOS profile can be reduced. For the
   purposes of this analysis, it is assumed that the RNIC must be
   able to operate in untrusted environments, which are open to DOS
   style attacks.

   Denial of service attacks against RNIC resources are not the
   typical unknown party spraying packets at a random host (such as
   a TCP SYN attack). Because the connection/Stream must be fully
   established, the attacker must be able to both send and receive
   messages over that connection/Stream, or be able to guess a valid
   packet on an existing RDMAP Stream.

   This section outlines the potential attacks and the
   countermeasures available for dealing with each attack.

7.5.1  RNIC Resource Consumption

   This section covers attacks that fall into the general category
   of a Local Peer attempting to unfairly allocate scarce (i.e.
   bounded) RNIC resources. The Local Peer may be attempting to
   allocate resources on its own behalf, or on behalf of a Remote
   Peer. Resources that fall into this category include: Protection
   Domains, Stream Context Memory, Translation and Protection
   Tables, and STag namespace. These can be attacks by currently
   active Local Peers or ones that allocated resources earlier, but
   are now idle.

   This type of attack can occur regardless of whether resources are
   shared across Streams.

   The allocation of all scarce resources MUST be placed under the
   control of a Privileged Resource Manager. This allows the
   Privileged Resource Manager to:

       *   prevent a Local Peer from allocating more than its fair
           share of resources.

       *   detect if a Remote Peer is attempting to launch a DOS
           attack by attempting to create an excessive number of
           Streams and take corrective action (such as refusing the
           request or applying network layer filters against the
           Remote Peer).

   This analysis assumes that the Resource Manager is responsible
   for handing out Protection Domains, and RNIC implementations will
   provide enough Protection Domains to allow the Resource Manager


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   to be able to assign a unique Protection Domain for each
   unrelated, untrusted Local Peer (for a bounded, reasonable number
   of Local Peers). This analysis further assumes that the Resource
   Manager implements policies to ensure that untrusted Local Peers
   are not able to consume all of the Protection Domains through a
   DOS attack. Note that Protection Domain consumption cannot result
   from a DOS attack launched by a Remote Peer, unless a Local Peer
   is acting on the Remote PeerÆs behalf.

7.5.2  Resource Consumption By Active Applications

   This section describes DOS attacks from Local and Remote Peers
   that are actively exchanging messages. Attacks on each RDMA NIC
   resource are examined and specific countermeasures are
   identified. Note that attacks on Stream Context Memory, Page
   Translation Tables, and STag namespace are covered in Section
   7.5.1 RNIC Resource Consumption, so are not included here.

7.5.2.1  Multiple Streams Sharing Receive Buffers

   The Remote Peer can attempt to consume more than its fair share
   of receive data buffers (Untagged DDP buffers or for RDMAP
   buffers consumed with Send Type Messages) if receive buffers are
   shared across multiple Streams.

   If resources are not shared across multiple Streams, then this
   attack is not possible because the Remote Peer will not be able
   to consume more buffers than were allocated to the Stream. The
   worst case scenario is that the Remote Peer can consume more
   receive buffers than the Local Peer allowed, resulting in no
   buffers to be available, which could cause the Remote PeerÆs
   Stream to the Local Peer to be torn down, and all allocated
   resources to be released.

   If local receive data buffers are shared among multiple Streams,
   then the Remote Peer can attempt to consume more than its fair
   share of the receive buffers, causing a different Stream to be
   short of receive buffers, thus possibly causing the other Stream
   to be torn down. For example, if the Remote Peer sent enough one
   byte Untagged Messages, they might be able to consume all local
   shared receive queue resources with little effort on their part.

   One method the Local Peer could use is to recognize that a Remote
   Peer is attempting to use more than its fair share of resources
   and terminate the Stream (causing the allocated resources to be
   released). However, if the Local Peer is sufficiently slow, it
   may be possible for the Remote Peer to still mount a denial of
   service attack. One countermeasure that can protect against this
   attack is implementing a low-water notification. The low-water
   notification alerts the application if the number of buffers in
   the receive queue is less than a threshold.



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   If all of the following conditions are true, then the Local Peer
   can size the amount of local receive buffers posted on the
   receive queue to ensure a DOS attack can be stopped.

       *   a low-water notification is enabled, and

       *   the Local Peer is able to bound the amount of time that
           it takes to replenish receive buffers, and

       *   the Local Peer maintains statistics to determine which
           Remote Peer is consuming buffers.

   The above conditions enable the low-water notification to arrive
   before resources are depleted and thus the Local Peer can take
   corrective action (e.g., terminate the Stream of the attacking
   Remote Peer).

   A different, but similar attack is if the Remote Peer sends a
   significant number of out-of-order packets and the RNIC has the
   ability to use the application buffer as a reassembly buffer. In
   this case the Remote Peer can consume a significant number of
   application buffers, but never send enough data to enable the
   application buffer to be completed to the application.

   An effective countermeasure is to create a high-water
   notification which alerts the application if there is more than a
   specified number of receive buffers "in process" (partially
   consumed, but not completed). The notification is generated when
   more than the specified number of buffers are in process
   simultaneously on a specific Stream (i.e., packets have started
   to arrive for the buffer, but the buffer has not yet been
   delivered to the ULP).

   A different countermeasure is for the RNIC Engine to provide the
   capability to limit the Remote PeerÆs ability to consume receive
   buffers on a per Stream basis. Unfortunately this requires a
   large amount of state to be tracked in each RNIC on a per Stream
   basis.

   Thus, if an RNIC Engine provides the ability to share receive
   buffers across multiple Streams, the combination of the RNIC
   Engine and the Privileged Resource Manager MUST be able to detect
   if the Remote Peer is attempting to consume more than its fair
   share of resources so that the Local Peer can apply
   countermeasures to detect and prevent the attack.

7.5.2.2  Local Peer Attacking a Shared CQ

   DOS attacks against a Shared Completion Queue (CQ) can be caused
   by either the Local Peer or the Remote Peer if either attempts to
   cause more completions than its fair share of the number of



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   entries, thus potentially starving another unrelated Stream such
   that no Completion Queue entries are available.

   A Completion Queue entry can potentially be consumed by a
   completion from the Send Queue or a Receive Queue completion. In
   the former, the attacker is the Local Peer. In the later, the
   attacker is the Remote Peer.

   A form of attack can occur where the Local Peers can consume
   resources on the CQ. A Local Peer that is slow to free resources
   on the CQ by not reaping the completion status quickly enough
   could stall all other Local Peers attempting to use that CQ.

   One of two countermeasures can be used to avoid this kind of
   attack. The first is to only share a CQ between Streams that
   share Partial Mutual Trust (i.e. Streams within the same
   Protection Domain). The other is to use a trusted Local Peer to
   act as a third party to free resources on the CQ and place the
   status in intermediate storage until the untrusted Local Peer
   reaps the status information. For these reasons, an RNIC MUST NOT
   enable sharing a CQ across Streams that belong to different
   Protection Domains. Addtionally, an application SHOULD NOT share
   a CQ between Streams which do not share Partial Mutual Trust.

7.5.2.3  Remote Peer Attacking a Shared CQ

   For an overview of the Shared CQ attack model, see Section
   7.5.2.2.

   The Remote Peer can attack a CQ by consuming more than its fair
   share of CQ entries by using one of the following methods:

       *   The ULP protocol allows the Remote Peer to reserve a
           specified number of CQ entries, possibly leaving
           insufficient entries for other Streams that are sharing
           the CQ.

       *   If the Remote Peer or Local Peer (or both) can attack the
           CQ by overwhelming the CQ with completions, then
           completion processing on other Streams sharing that
           Completion Queue can be affected (e.g. the Completion
           Queue overflows and stops functioning).

   The first method of attack can be avoided if the ULP does not
   allow a Remote Peer to reserve CQ entries or there is a trusted
   intermediary such as a Privileged Resource Manager. Unfortunately
   it is often unrealistic to not allow a Remote Peer to reserve CQ
   entries - particularly if the number of completion entries is
   dependent on other ULP negotiated parameters, such as the amount
   of buffering required by the ULP. Thus an implementation MUST
   implement a Privileged Resource Manager to control the allocation



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   of CQ entries. See Section 4.1 Components on page 9 for a
   definition of Privileged Resource Manager.

   One way that a Local or Remote Peer can attempt to overwhelm a CQ
   with completions is by sending minimum length RDMAP/DDP Messages
   to cause as many completions (receive completions for the Remote
   Peer, send completions for the Local Peer) per second as
   possible. If it is the Remote Peer attacking, and we assume that
   the Local Peer does not run out of receive buffers (if they do,
   then this is a different attack, documented in Section 7.5.2.1
   Multiple Streams Sharing Receive Buffers on page 30), then it
   might be possible for the Remote Peer to consume more than its
   fair share of Completion Queue entries. Depending upon the CQ
   implementation, this could either cause the CQ to overflow (if it
   is not large enough to handle all of the completions generated)
   or for another Stream to not be able to generate CQ entries (if
   the RNIC had flow control on generation of CQ entries into the
   CQ). In either case, the CQ will stop functioning correctly and
   any Streams expecting completions on the CQ will stop
   functioning.

   This attack can occur regardless of whether all of the Streams
   associated with the CQ are in the same Protection Domain or are
   in different Protection Domains - the key issue is that the
   number of Completion Queue entries is less than the number of all
   outstanding operations that can cause a completion.

   The Local Peer can protect itself from this type of attack using
   either of the following methods:

       *   Size the CQ to the appropriate level, as specified below
           (note that if the CQ currently exists, and it needs to be
           resized, resizing the CQ can fail, so the CQ resize
           should be done before sizing the Send Queue and Receive
           Queue on the Stream), OR

       *   Grant fewer resources than the Remote Peer requested (not
           supplying the number of Receive Data Buffers requested).

   The proper sizing of the CQ is dependent on whether the Local
   Peer will post as many resources to the various queues as the
   size of the queue enables or not. If the Local Peer can be
   trusted to post a number of resources that is smaller than the
   size of the specific resourceÆs queue, then a correctly sized CQ
   means that the CQ is large enough to hold completion status for
   all of the outstanding Data Buffers (both send and receive
   buffers), or:







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            CQ_MIN_SIZE = SUM(MaxPostedOnEachRQ)
                          + SUM(MaxPostedOnEachSRQ)
                          + SUM(MaxPostedOnEachSQ)

   Where:

           MaxPostedOnEachRQ = the maximum number of requests which
                  can cause a completion that will be posted on a
                  specific Receive Queue.

           MaxPostedOnEachSRQ = the maximum number of requests which
                  can cause a completion that will be posted on a
                  specific Shared Receive Queue.

           MaxPostedOnEachSQ = the maximum number of requests which
                  can cause a completion that will be posted on a
                  specific Send Queue.

   If the local peer must be able to completely fill the queues, or
   can not be trusted to observe a limit smaller than the queues,
   then the CQ must be sized to accommodate the maximum number of
   operations that it is possible to post at any one time. Thus the
   equation becomes:

            CQ_MIN_SIZE = SUM(SizeOfEachRQ)
                          + SUM(SizeOfEachSRQ)
                          + SUM(SizeOfEachSQ)

   Where:

          SizeOfEachRQ = the maximum number of requests which
                  can cause a completion that can ever be posted
                  on a specific Receive Queue.

          SizeOfEachSRQ = the maximum number of requests which
                  can cause a completion that can ever be posted
                  on a specific Shared Receive Queue.

          SizeOfEachSQ = the maximum number of requests which
                  can cause a completion that can ever be posted
                  on a specific Send Queue.

   Where MaxPosted*OnEach*Q and SizeOfEach*Q varies on a per Stream
   or per Shared Receive Queue basis.

   The Local Peer MUST implement a mechanism to ensure that the
   Completion Queue can not overflow. Note that it is possible to
   share CQs even if the Remote Peers accessing the CQs are
   untrusted if either of the above two formulas are implemented. If
   the Local Peer can be trusted to not post more than
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   then the first formula applies. If the Local Peer can not be
   trusted to obey the limit, then the second formula applies.

7.5.2.4  Attacking the RDMA Read Request Queue

   If RDMA Read Request Queue resources are pooled across multiple
   Streams, one attack is if the Local Peer attempts to unfairly
   allocate RDMA Read Request Queue resources for its Streams. For
   example, the Local Peer attempts to allocate all available
   resources on a specific RDMA Read Request Queue for its Streams,
   thereby denying the resource to applications sharing the RDMA
   Read Request Queue. The same type of argument applies even if the
   RDMA Read Request is not shared - but a Local Peer attempts to
   allocate all of the RNICs resource when the queue is created.

   Thus access to interfaces that allocate RDMA Read Request Queue
   entries MUST be restricted to a trusted Local Peer, such as a
   Privileged Resource Manager. The Privileged Resource Manager
   SHOULD prevent a Local Peer from allocating more than its fair
   share of resources.

   Another form of attack is if the Remote Peer sends more RDMA Read
   Requests than the depth of the RDMA Read Request Queue at the
   Local Peer. If the RDMA Read Request Queue is a shared resource,
   this could corrupt the queue. If the queue is not shared, then
   the worst case is that the current Stream is disabled. One
   approach to solving the shared RDMA Read Request Queue would be
   to create thresholds, similar to those described in Section
   7.5.2.1 Multiple Streams Sharing Receive Buffers on page 30. A
   simpler approach is to not share RDMA Read Request Queue
   resources amoung Streams or enforce hard limits of consumption
   per Stream. Thus RDMA Read Request Queue resource consumption
   MUST be controlled such that RDMAP/DDP Streams which do not share
   Partial Mutual Trust do not share RDMA Read Request Queue
   resources.

   If the issue is a bug in the Remote PeerÆs implementation, and
   not a malicious attack, the issue can be solved by requiring the
   Remote PeerÆs RNIC to throttle RDMA Read Requests. By properly
   configuring the Stream at the Remote Peer through a trusted
   agent, the RNIC can be made to not transmit RDMA Read Requests
   that exceed the depth of the RDMA Read Request Queue at the Local
   Peer. If the Stream is correctly configured, and if the Remote
   Peer submits more requests than the Local PeerÆs RDMA Read
   Request Queue can handle, the requests would be queued at the
   Remote PeerÆs RNIC until previous requests complete. If the
   Remote PeerÆs Stream is not configured correctly, the RDMAP
   Stream is terminated when more RDMA Read Requests arrive at the
   Local Peer than the Local Peer can handle (assuming the prior
   paragraphÆs recommendation is implemented). Thus an RNIC
   implementation MUST provide a mechanism to cap the number of
   outstanding RDMA Read Requests.


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7.5.3  Resource Consumption by Idle Applications

   The simplest form of a DOS attack given a fixed amount of
   resources is for the Remote Peer to create a RDMAP Stream to a
   Local Peer, and request dedicated resources then do no actual
   work. This allows the Remote Peer to be very light weight (i.e.
   only negotiate resources, but do no data transfer) and consumes a
   disproportionate amount of resources in the server.

   A general countermeasure for this style of attack is to monitor
   active RDMAP Streams and if resources are getting low, reap the
   resources from RDMAP Streams that are not transferring data and
   possibly terminate the Stream. This would presumably be under
   administrative control.

   Refer to Section 7.5.1 for the analysis and countermeasures for
   this style of attack on the following RNIC resources: Stream
   Context Memory, Page Translation Tables and STag namespace.

   Note that some RNIC resources are not at risk of this type of
   attack from a Remote Peer because an attack requires the Remote
   Peer to send messages in order to consume the resource. Receive
   Data Buffers, Completion Queue, and RDMA Read Request Queue
   resources are examples. These resources are, however, at risk
   from a Local Peer that attempts to allocate resources, then goes
   idle. This could also be created if the ULP negotiates the
   resource levels with the Remote Peer, which causes the Local Peer
   to consume resources, however the Remote Peer never sends data to
   consume them. The general countermeasure described in this
   section can be used to free resources allocated by an idle Local
   Peer.

7.5.4  Exercise of non-optimal code paths

   Another form of DOS attack is to attempt to exercise data paths
   that can consume a disproportionate amount of resources. An
   example might be if error cases are handled on a "slow path"
   (consuming either host or RNIC computational resources), and an
   attacker generates excessive numbers of errors in an attempt to
   consume these resources. Note that for most RDMAP or DDP errors,
   the attacking Stream will simply be torn down. Thus for this form
   of attack to be effective, the Remote Peer needs to exercise data
   paths which do not cause the Stream to be torn down.

   If an RNIC implementation contains "slow paths" which do not
   result in the tear down of the Stream, it is recommended that an
   implementation provide the ability to detect the above condition
   and allow an administrator to act, including potentially
   administratively tearing down the RDMAP Stream associated with
   the Stream exercising data paths consuming a disproportionate
   amount of resources.



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7.5.5  Remote Invalidate an STag Shared on Multiple Streams

   If a Local Peer has enabled an STag for remote access, the Remote
   Peer could attempt to remote invalidate the STag by using the
   RDMAP Send with Invalidate or Send with SE and Invalidate
   Message. If the STag is only valid on the current Stream, then
   the only side effect is that the Remote Peer can no longer use
   the STag; thus there are no security issues.

   If the STag is valid across multiple Streams, then the Remote
   Peer can prevent other Streams from using that STag by using the
   remote invalidate functionality.

   Thus if RDDP Streams do not share Partial Mutual Trust (i.e. the
   Remote Peer may attempt to invalidate the STag prematurely), the
   application MUST NOT allow an STag to be valid across multiple
   Streams.

7.6  Elevation of Privilege

   The RDMAP/DDP Security Architecture explicitly differentiates
   between three levels of privilege - Non-Privileged, Privileged,
   and the Privileged Resource Manager. If a Non-Privileged
   Application is able to elevate its privilege level to a
   Privileged Application, then mapping a physical address list to
   an STag can provide local and remote access to any physical
   address location on the node. If a Privileged Mode Application is
   able to promote itself to be a Resource Manager, then it is
   possible for it to perform denial of service type attacks where
   substantial amounts of local resources could be consumed.

   In general, elevation of privilege is a local implementation
   specific issue and thus outside the scope of this specification.

   There is one issue worth noting, however. If the RNIC
   implementation, by some insecure mechanism (or implementation
   defect), can enable a Remote Peer or un-trusted Local Peer to
   load firmware into the RNIC Engine, it is possible to use the
   RNIC to attack the host. Thus, an implementation MUST NOT enable
   firmware to be loaded on the RNIC Engine directly from a Remote
   Peer, unless the Remote Peer is properly authenticated (by a
   mechanism outside the scope of this specification. The mechanism
   presumably entails authenticating that the remote application has
   the right to perform the update), and the update is done via a
   secure protocol, such as IPsec (See Section 8 Security Services
   for RDMA and DDP on page 38). Further, an implementation MUST NOT
   allow a Non-Privileged Local Peer to update firmware in the RNIC
   Engine.






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8  Security Services for RDMA and DDP

   RDMA and DDP are used to control, read and write data buffers
   over IP networks. Therefore, the control and the data packets of
   these protocols are vulnerable to the spoofing, tampering and
   information disclosure attacks listed in Section 7.

   Generally speaking, Stream confidentiality protects against
   eavesdropping. Stream and/or session authentication and integrity
   protection is a counter measurement against various spoofing and
   tampering attacks. The effectiveness of authentication and
   integrity against a specific attack, depend on whether the
   authentication is machine level authentication (as the one
   provided by IPsec and SSL), or ULP authentication.

8.1  Introduction to Security Options

   The following security services can be applied to an RDMAP/DDP
   Stream:

   1.  Session confidentiality - protects against eavesdropping
       (section 7.4.9).

   2.  Per-packet data source authentication - protects against the
       following spoofing attacks: network based impersonation
       (section 7.2.1), Stream hijacking (section 7.2.2), and man in
       the middle (section 7.2.3).

   3.  Per-packet integrity - protects against tampering done by
       network based modification of buffer content (section 7.3.4)

   4.  Packet sequencing - protects against replay attacks, which is
       a special case of the above tampering attack.

   If an RDMAP/DDP Stream may be subject to impersonation attacks,
   or Stream hijacking attacks, it is recommended that the Stream be
   authenticated, integrity protected, and protected from replay
   attacks; it MAY use confidentiality protection to protect from
   eavesdropping (in case the RDMAP/DDP Stream traverses a public
   network).

   Both IPsec and SSL are capable of providing the above security
   services for IP and TCP traffic respectively. ULP protocols are
   able to provide only part of the above security services. The
   next sections describe the different security options.

8.1.1  Introduction to IPsec

   IPsec is a protocol suite which is used to secure communication
   at the network layer between two peers. The IPsec protocol suite
   is specified within the IP Security Architecture [RFC2401], IKE
   [RFC2409], IPsec Authentication Header (AH) [RFC2402] and IPsec


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   Encapsulating Security Payload (ESP) [RFC2406] documents. IKE is
   the key management protocol while AH and ESP are used to protect
   IP traffic.

   An IPsec SA is a one-way security association, uniquely
   identified by the 3-tuple: Security Parameter Index (SPI),
   protocol (ESP/AH) and destination IP address. The parameters for
   an IPsec security association are typically established by a key
   management protocol. These include the encapsulation mode,
   encapsulation type, session keys and SPI values.

   IKE is a two phase negotiation protocol based on the modular
   exchange of messages defined by ISAKMP [RFC2408],and the IP
   Security Domain of Interpretation (DOI) [RFC2407]. IKE has two
   phases, and accomplishes the following functions:

   1.  Protected cipher suite and options negotiation - using keyed
       MACs and encryption and anti-replay mechanisms.

   2.  Master key generation - via Diffie-Hellman calculations.

   3.  Authentication of end-points (usually machine level
       authentication).

   4.  IPsec SA management (selector negotiation, options
       negotiation, create, delete, and rekeying).

   Items 1 through 3 are accomplished in IKE Phase 1, while item 4
   is handled in IKE Phase 2.

   IKE phase 1 defines four authentication methods; three of them
   require both sides to have certified signature or encryption
   public keys; the forth require the side to exchange out-of-band a
   secret random string - called pre-shared-secret (PSS).

   An IKE Phase 2 negotiation is performed to establish both an
   inbound and an outbound IPsec SA. The traffic to be protected by
   an IPsec SA is determined by a selector which has been proposed
   by the IKE initiator and accepted by the IKE Responder. The IPsec
   SA selector can be a "filter" or traffic classifier, defined as
   the 5-tuple: <Source IP address, Destination IP address,
   transport protocol (e.g. UDP/SCTP/TCP), Source port, Destination
   port>. The successful establishment of a IKE Phase-2 SA results
   in the creation of two uni-directional IPsec SAs fully qualified
   by the tuple <Protocol (ESP/AH), destination address, SPI>.

   The session keys for each IPsec SA are derived from a master key,
   typically via a MODP Diffie-Hellman computation. Rekeying of an
   existing IPsec SA pair is accomplished by creating two new IPsec
   SAs, making them active, and then optionally deleting the older
   IPsec SA pair. Typically the new outbound SA is used immediately,
   and the old inbound SA is left active to receive packets for some


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   locally defined time, perhaps 30 seconds or 1 minute. Optionally,
   rekeying can use Diffie-Helman for keying material generation.

8.1.2  Introduction to SSL Limitations on RDMAP

   SSL and TLS [RFC 2246] provide Stream authentication, integrity
   and confidentiality for TCP based applications. SSL supports one-
   way (server only) or mutual certificates based authentication.

   There are at least two limitations that make SSL underneath RDMAP
   less appropriate then IPsec for DDP/RDMA security:

   1.  The maximum length supported by the TLS record layer protocol
       is 2^14 bytes - longer packets must be fragmented (as a
       comparison, the maximal length of an IPsec packet is
       determined by the maximum length of an IP packet).

   2.  SSL is a connection oriented protocol. If a stream cipher or
       block cipher in CBC mode is used for bulk encryption, then a
       packet can be decrypted only after all the packets preceding
       it have already arrived. If SSL is used to protect DDP/RDMA
       traffic, then SSL must gather all out-of-order packets before
       RDMAP/DDP can place them into the ULP buffer, which might
       cause a significant decrease in its efficiency.

   If SSL is layered on top of RDMAP or DDP, SSL does not protect
   the RDMAP and/or DDP headers. Thus a man-in-the-middle attack can
   still occur by modifying the RDMAP/DDP header to incorrectly
   place the data into the wrong buffer, thus effectively corrupting
   the data stream.

8.1.3  Applications Which Provide Security

   Issue: Guidance for application protocols like NFS which
   implement security <TBD>.


8.2  Requirements for IPsec Encapsulation of DDP

   The IP Storage working group has spent significant time and
   effort to define the normative IPSec requirements for IP Storage
   [RFC3723]. Portions of that specification are applicable to a
   wide variety of protocols, including the RDDP protocol suite. In
   order to not replicate this effort, an RNIC implementation MUST
   follow the requirements defined in RFC3723 Section 2.3 and
   Section 5, including the associated normative references for
   those sections.

   Additionally, since IPsec acceleration hardware may only be able
   to handle a limited number of active IKE Phase 2 SAs, Phase 2
   delete messages may be sent for idle SAs, as a means of keeping
   the number of active Phase 2 SAs to a minimum. The receipt of an


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   IKE Phase 2 delete message MUST NOT be interpreted as a reason
   for tearing down an DDP/RDMA Stream. Rather, it is preferable to
   leave the Stream up, and if additional traffic is sent on it, to
   bring up another IKE Phase 2 SA to protect it. This avoids the
   potential for continually bringing Streams up and down.

   Note that there are serious security issues if IPSec is not
   implemented end-to-end. For example, if IPSec is implemented as a
   tunnel in the middle of the network, any hosts between the peer
   and the IPSec tunneling device can freely attack the unprotected
   Stream.











































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9  Security considerations

   This entire specification is focused on security considerations.



















































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10 References

10.1 Normative References

   [RFC2828] Shirley, R., "Internet Security Glossary", FYI 36, RFC
       2828, May 2000.

   [DDP] Shah, H., J. Pinkerton, R.Recio, and P. Culley, "Direct
       Data Placement over Reliable Transports", Internet-Draft
       draft-ietf-rddp-ddp-01.txt, February 2003.

   [RDMAP] Recio, R., P. Culley, D. Garcia, J. Hilland, "An RDMA
       Protocol Specification", Internet-Draft draft-ietf-rddp-
       rdmap-01.txt, February 2003.

   [RFC3723] Aboba B., et al, "Securing Block Storage Protocols over
       IP", Internet draft (work in progress), RFC3723, April 2004.

   [SCTP] R. Stewart et al., "Stream Control Transmission Protocol",
       RFC 2960, October 2000.

   [TCP] Postel, J., "Transmission Control Protocol - DARPA Internet
       Program Protocol Specification", RFC 793, September 1981.

10.2 Informative References

   [IPv6-Trust] Nikander, P., J.Kempf, E. Nordmark, "IPv6 Neighbor
       Discovery trust modelsTrust Models and threats", Internet-
       Draft draft-ietf-send-psreq-01.txt, January 2003.

























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11 Appendix A: Implementing Client/Server Protocols

   <TBD: This section has not been updated to reflect the new
   normative focus of this specification. It will be updated in the
   next version.>

   The prior sections outlined specific attacks and their
   countermeasures. This section summarizes the attacks and
   countermeasures defined in the prior section which are applicable
   to creation of a secure application server. An application server
   is defined as an application which must be able to communicate
   with many clients which do not trust each other and ensure that
   each client can not attack another client through server
   interactions. Further, the server may wish to use multiple
   Streams to communicate with a specific client, and those Streams
   may share mutual trust.

   All of the prior section's details on attacks and countermeasures
   to protect a single Stream apply to the server. This section
   focuses on security issues where multiple clients are talking
   with a single server, and what mitigations the server application
   must have in place to ensure robust operation.

   The following list summarizes the relevent attacks that clients
   can mount on the shared server, by re-stating the previous
   normative statements to be client/server specific:

       *   General Requirements

           *   Section 4.1 Components on page 9. To ensure Non-
               Privileged applications running on the server can not
               create a DOS attack on each other, all Non-Privileged
               Application interactions with the RNIC Engine that
               could affect other applications MUST be done using
               the Privileged Resource Manager as a proxy.

       *   Spoofing

           *   For protection against many forms of spoofing
               attacks, enable IPSec.

           *   Section 7.2.4 Using an STag on a Different Stream on
               page 23. To ensure that one client can not access
               another client's data via use of the other client's
               STag, the server MUST either scope an STag to a
               single Stream or use a Protection Domain per client.
               If a single client has multiple streams that share
               Partial Mutual Trust, then the STag can be shared
               between the associated Streams by using a single
               Protection Domain amoung the associated Streams. To
               prevent unintended sharing of STags within the
               associated Streams, an implementation SHOULD allocate


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               STags in such a fashion that it is difficult to
               predict the next allocated STag number.

       *   Tampering

           *   7.3.1 Buffer Overrun - RDMA Write or Read Response on
               page 24. To ensure a client can not intentionally or
               accidentally cause a buffer overrun, an RNIC
               implementation MUST ensure that a Remote Peer is not
               able to access memory outside of the buffer specified
               when the STag was enabled for remote access.

           *   7.3.3 Multiple STags to access the same buffer on
               page 25. See the following bullet's discussion of
               Section 7.4.6.

       *   Information Disclosure

           *   7.4.2 Using RDMA Read to Access Stale Data on page
               26. A server SHOULD ensure that no stale data is
               contained in a buffer before remote read access
               rights are granted to a client (this can be done by
               zeroing the contents of the memory, for example).

           *   7.4.5 RDMA Read into an RDMA Write Buffer on page 27.
               It is RECOMMENDED that if a server only intends a
               buffer to be exposed for remote write access, it set
               the access rights to the buffer to only enable remote
               write access.

           *   7.4.6 Using Multiple STags Which Alias to the Same
               Buffer on page 27. It is RECOMMENDED that separate
               clients not be granted write access to the same
               buffer through different STags. A buffer should be
               exposed to only one client at a time to ensure that
               no information disclosure or information tampering
               occurs between peers.

       *   Denial of Service

           *   7.5.1 RNIC Resource Consumption on page 29. It is
               RECOMMENDED that the server place the allocation of
               all scarce resources be placed under the control of a
               Privileged Resource Manager.

           *   7.5.2.1 Multiple Streams Sharing Receive Buffers on
               page 30. If an RNIC Engine provides the ability to
               share receive buffers across multiple Streams, it is
               RECOMMENDED that it enable the server to detect if
               the client is attempting to consume more than its
               fair share of resources so that the server can apply
               countermeasures to detect and prevent the attack.


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           *   7.5.2.2 Local Peer Attacking a Shared CQ on page 31.
               Sharing a CQ across Streams that belong to different
               Protection Domains is NOT RECOMMENDED.

           *   7.5.2.3 Remote Peer Attacking a Shared CQ on page 32.
               If a server allows the client to influence CQ entry
               resource allocation, then it is RECOMMENDED that the
               CQ be isolated to Streams within a single Protection
               Domain (i.e. streams that share Partial Mutual
               Trust).

               It is RECOMMENDED that the Local Peer implement a
               mechanism to ensure that the Completion Queue can not
               overflow.

           *   7.5.2.4 Attacking the RDMA Read Request Queue on page
               35. It is RECOMMENDED that access to interfaces that
               allocate RDMA Read Request Queue entries be
               restricted to a trusted Local Peer, such as a
               Privileged Resource Manager.

               It is RECOMMENDED that RDMA Read Request Queue
               resource consumption be controlled such that
               RDMAP/DDP Streams which do not share Partial Mutual
               Trust do not share RDMA Read Request Queue resources.

           *   7.5.3 Resource Consumption by Idle Applications on
               page 36. Refer to Section 7.5.1.

           *   7.5.5 Remote Invalidate an STag Shared on Multiple
               Streams on page 37. If DDP/RDMAP Streams do not share
               Partial Mutual Trust (i.e. the client may attempt to
               invalidate the STag prematurely), it is NOT
               RECOMMENDED that the server allow an STag to be valid
               across multiple Streams.



















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12 Appendix B: Summary Table of Attacks

   Below is a summary of implementation requirements for the RNIC:

       *   7.3.1 Buffer Overrun - RDMA Write or Read Response

       *   7.4.8 Controlling Access to PTT & STag Mapping

       *   7.5.1 RNIC Resource Consumption

       *   7.5.2.1 Multiple Streams Sharing Receive Buffers

       *   7.5.2.2 Local Peer Attacking a Shared CQ

       *   7.5.2.3 Remote Peer Attacking a Shared CQ

       *   7.5.2.4 Attacking the RDMA Read Request Queue

       *   7.5.4 Exercise of non-optimal code paths

       *   7.6 Elevation of Privilege

   Below is a summary of implementation requirements for the
   application above the RNIC:

       *   7.2.4 Using an STag on a Different Stream

       *   7.3.2 Modifying a Buffer After Indication

       *   7.4.2 Using RDMA Read to Access Stale Data

       *   7.4.3 Accessing a Buffer After the Transfer

       *   7.4.4 Accessing Unintended Data With a Valid STag

       *   7.4.5 RDMA Read into an RDMA Write Buffer

       *   7.4.6 Using Multiple STags Which Alias to the Same Buffer

       *   7.5.2.2 Local Peer Attacking a Shared CQ

       *   7.5.5 Remote Invalidate an STag Shared on Multiple
           Streams











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13 Appendix C: Partial Trust Taxonomy

   Partial Trust is defined as when one party is willing to assume
   that another party will refrain from a specific attack or set of
   attacks, the parties are said to be in a state of Partial Trust.
   Note that the partially trusted peer may attempt a different set
   of attacks. This may be appropriate for many applications where
   any adverse effects of the betrayal is easily confined and does
   not place other clients or applications at risk.

   The Trust Models described in this section have three primary
   distinguishing characteristics. The Trust Model refers to a Local
   Peer and Remote Peer, which are the local and remote application
   instances communicating via RDMA/DDP.

       *   Local Resource Sharing (yes/no) - When local resources
           are shared, they are shared across a grouping of
           RDMAP/DDP Streams. If local resources are not shared, the
           resources are dedicated on a per Stream basis. Resources
           are defined in Section 4.2 - Resources on page 11. The
           advantage of not sharing resources between Streams is
           that it reduces the types of attacks that are possible.
           The disadvantage is that applications might run out of
           resources.

       *   Local Partial Trust (yes/no) - Local Partial Trust is
           determined based on whether the local grouping of
           RDMAP/DDP Streams (which typically equates to one
           application or group of applications) mutually trust each
           other to not perform a specific set of attacks.

       *   Remote Partial Trust (yes/no) - The Remote Partial Trust
           level is determined based on whether the Local Peer of a
           specific RDMAP/DDP Stream partially trusts the Remote
           Peer of the Stream (see the definition of Partial Trust
           in Section 3 Introduction).

   Not all of the combinations of the trust characteristics are
   expected to be used by applications. This paper specifically
   analyzes five application Trust Models that are expected to be in
   common use. The Trust Models are as follows:

       *   NS-NT - Non-Shared Local Resources, no Local Trust, no
           Remote Trust - typically a server application that wants
           to run in the safest mode possible. All attack
           mitigations are in place to ensure robust operation.

       *   NS-RT - Non-Shared Local Resources, no Local Trust,
           Remote Partial Trust - typically a peer-to-peer
           application, which has, by some method outside of the
           scope of this specification, authenticated the Remote
           Peer. Note that unless some form of key based


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           authentication is used on a per RDMA/DDP Stream basis, it
           may not be possible be possible for man-in-the-middle
           attacks to occur. See section 8, Security Services for
           RDMA and DDP on page 38.

       *   S-NT - Shared Local Resources, no Local Trust, no Remote
           Trust - typically a server application that runs in an
           untrusted environment where the amount of resources
           required is either too large or too dynamic to dedicate
           for each RDMAP/DDP Stream.

       *   S-LT - Shared Local Resources, Local Partial Trust, no
           Remote Trust - typically an application, which provides a
           session layer and uses multiple Streams, to provide
           additional throughput or fail-over capabilities. All of
           the Streams within the local application partially trust
           each other, but do not trust the Remote Peer. This trust
           model may be appropriate for embedded environments.

       *   S-T - Shared Local Resources, Local Partial Trust, Remote
           Partial Trust - typically a distributed application, such
           as a distributed database application or a High
           Performance Computer (HPC) application, which is intended
           to run on a cluster. Due to extreme resource and
           performance requirements, the application typically
           authenticates with all of its peers and then runs in a
           highly trusted environment. The application peers are all
           in a single application fault domain and depend on one
           another to be well-behaved when accessing data
           structures. If a trusted Remote Peer has an
           implementation defect that results in poor behavior, the
           entire application could be corrupted.

   Models NS-NT and S-NT above are typical for Internet networking -
   neither Local Peers nor the Remote Peer is trusted. Sometimes
   optimizations can be done that enable sharing of Page Translation
   Tables across multiple Local Peers, thus Model S-LT can be
   advantageous. Model S-T is typically used when resource scaling
   across a large parallel application makes it infeasible to use
   any other model. Resource scaling issues can either be due to
   performance around scaling or because there simply are not enough
   resources. Model NS-RT is probably the least likely model to be
   used, but is presented for completeness.











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14 AuthorÆs Addresses

   James Pinkerton
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA. 98052 USA
   Phone: +1 (425) 705-5442
   Email: jpink@windows.microsoft.com

   Ellen Deleganes
   Intel Corporation
   MS JF5-355
   2111 NE 25th Ave.
   Hillsboro, OR 97124 USA
   Phone: +1 (503) 712-4173
   Email: ellen.m.deleganes@intel.com

   Sara Bitan
   Microsoft Corporation
   Email: sarab@microsoft.com


































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15 Acknowledgments

   Allyn Romanow
   Cisco Systems
   170 W Tasman Drive
   San Jose, CA 95134 USA
   Phone: +1 408 525 8836
   Email: allyn@cisco.com

   Catherine Meadows
   Naval Research Laboratory
   Code 5543
   Washington, DC 20375
   Email: meadows@itd.nrl.navy.mil

   Patricia Thaler
   Agilent Technologies, Inc.
   1101 Creekside Ridge Drive, #100
   M/S-RG10
   Roseville, CA 95678
   Phone: +1-916-788-5662
   email: pat_thaler@agilent.com

   James Livingston
   NEC Solutions (America), Inc.
   7525 166th Ave. N.E., Suite D210
   Redmond, WA 98052-7811
   Phone: +1 (425) 897-2033
   Email: james.livingston@necsam.com

   John Carrier
   Adaptec, Inc.
   691 S. Milpitas Blvd.
   Milpitas, CA 95035 USA
   Phone: +1 (360) 378-8526
   Email: john_carrier@adaptec.com

   Caitlin Bestler
   Email: cait@asomi.com

   Bernard Aboba
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA. 98052 USA
   Phone: +1 (425) 706-6606
   Email: bernarda@windows.microsoft.com








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16 Full Copyright Statement

   Copyright (C) The Internet Society (2001). All Rights Reserved.

   This document and translations of it may be copied and furnished
   to others, and derivative works that comment on or otherwise
   explain it or assist in its implementation may be prepared,
   copied, published and distributed, in whole or in part, without
   restriction of any kind, provided that the above copyright notice
   and this paragraph are included on all such copies and derivative
   works. However, this document itself may not be modified in any
   way, such as by removing the copyright notice or references to
   the Internet Society or other Internet organizations, except as
   needed for the purpose of developing Internet standards in which
   case the procedures for copyrights defined in the Internet
   Standards process must be followed, or as required to translate
   it into languages other than English.

   The limited permissions granted above are perpetual and will not
   be revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on
   an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
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   OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
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   Funding for the RFC Editor function is currently provided by the
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