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CWE-1311: Improper Translation of Security Attributes by Fabric Bridge

Weakness ID: 1311
Abstraction: Base
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
The bridge incorrectly translates security attributes from either trusted to untrusted or from untrusted to trusted when converting from one fabric protocol to another.
+ Extended Description

A bridge allows IP blocks supporting different fabric protocols to be integrated into the system. Fabric end-points or interfaces usually have dedicated signals to transport security attributes. For example, HPROT signals in AHB, AxPROT signals in AXI, and MReqInfo and SRespInfo signals in OCP.

The values on these signals are used to indicate the security attributes of the transaction. These include the immutable hardware identity of the controller initiating the transaction, privilege level, and type of transaction (e.g., read/write, cacheable/non-cacheable, posted/non-posted).

A weakness can arise if the bridge IP block, which translates the signals from the protocol used in the IP block endpoint to the protocol used by the central bus, does not properly translate the security attributes. As a result, the identity of the initiator could be translated from untrusted to trusted or vice-versa. This could result in access-control bypass, privilege escalation, or denial of service.

+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
ChildOfPillarPillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.284Improper Access Control
+ Relevant to the view "Hardware Design" (CWE-1194)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1203Peripherals, On-chip Fabric, and Interface/IO Problems
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Architecture and Design
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Verilog (Undetermined Prevalence)

VHDL (Undetermined Prevalence)


Class: Technology-Independent (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Access Control

Technical Impact: Modify Memory; Read Memory; Gain Privileges or Assume Identity; Bypass Protection Mechanism; Execute Unauthorized Code or Commands

+ Demonstrative Examples

Example 1

The bridge interfaces between OCP and AHB end points. OCP uses MReqInfo signal to indicate security attributes, whereas AHB uses HPROT signal to indicate the security attributes. The width of MReqInfo can be customized as needed. In this example, MReqInfo is 5-bits wide and carries the privilege level of the OCP controller.

The values 5’h11, 5’h10, 5’h0F, 5’h0D, 5’h0C, 5’h0B, 5’h09, 5’h08, 5’h04, and 5’h02 in MReqInfo indicate that the request is coming from a privileged state of the OCP bus controller. Values 5’h1F, 5’h0E, and 5’h00 indicate untrusted, privilege state.

Though HPROT is a 5-bit signal, we only consider the lower, two bits in this example. HPROT values 2’b00 and 2’b10 are considered trusted, and 2’b01 and 2’b11 are considered untrusted.

The OCP2AHB bridge is expected to translate trusted identities on the controller side to trusted identities on the responder side. Similarly, it is expected to translate untrusted identities on the controller side to untrusted identities on the responder side.

(bad code)
Example Language: Verilog 
module ocp2ahb

output [1:0] ahb_hprot; // output is 2 bit signal for AHB HPROT
input [4:0] ocp_mreqinfo; // input is 5 bit signal from OCP MReqInfo
wire [6:0] p0_mreqinfo_o_temp; // OCP signal that transmits hardware identity of bus controller

wire y;
reg [1:0] ahb_hprot;

// hardware identity of bus controller is in bits 5:1 of p0_mreqinfo_o_temp signal
assign p0_mreqinfo_o_temp[6:0] = {1'b0, ahb_hprot[4:0], y};

always @*

case (p0_mreqinfo_o_temp[4:2])
000: ahb_hprot = 2'b11; // OCP MReqInfo to AHB HPROT mapping
001: ahb_hprot = 2'b00;
010: ahb_hprot = 2'b00;
011: ahb_hprot = 2'b01;
100: ahb_hprot = 2'b00;
101: ahb_hprot = 2'b00;
110: ahb_hprot = 2'b10;
111: ahb_hprot = 2'b00;

Logic in the case statement only checks for MReqInfo bits 4:2, i.e., hardware-identity bits 3:1. When ocp_mreqinfo is 5’h1F or 5’h0E, p0_mreqinfo_o_temp[2] will be 1. As a result, untrusted IDs from OCP 5’h1F and 5’h0E get translated to trusted ahb_hprot values 2’b00.

+ Potential Mitigations

Phase: Architecture and Design

The translation must map signals in such a way that untrusted agents cannot map to trusted agents or vice-versa.

Phase: Implementation

Ensure that the translation maps signals in such a way that untrusted agents cannot map to trusted agents or vice-versa.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2020-05-24Arun Kanuparthi, Hareesh Khattri, Parbati MannaIntel Corporation
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Page Last Updated: December 10, 2020