CVE-2023-52608

In the Linux kernel, the following vulnerability has been resolved:

firmware: arm_scmi: Check mailbox/SMT channel for consistency

On reception of a completion interrupt the shared memory area is accessed to retrieve the message header at first and then, if the message sequence number identifies a transaction which is still pending, the related payload is fetched too.

When an SCMI command times out the channel ownership remains with the platform until eventually a late reply is received and, as a consequence, any further transmission attempt remains pending, waiting for the channel to be relinquished by the platform.

Once that late reply is received the channel ownership is given back to the agent and any pending request is then allowed to proceed and overwrite the SMT area of the just delivered late reply; then the wait for the reply to the new request starts.

It has been observed that the spurious IRQ related to the late reply can be wrongly associated with the freshly enqueued request: when that happens the SCMI stack in-flight lookup procedure is fooled by the fact that the message header now present in the SMT area is related to the new pending transaction, even though the real reply has still to arrive.

This race-condition on the A2P channel can be detected by looking at the channel status bits: a genuine reply from the platform will have set the channel free bit before triggering the completion IRQ.

Add a consistency check to validate such condition in the A2P ISR.

Weakness

The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.

Affected Software

Extended Description

This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider. A race condition occurs within concurrent environments, and is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. Programmers may assume that certain code sequences execute too quickly to be affected by an interfering code sequence; when they are not, this violates atomicity. For example, the single “x++” statement may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read (the original value of x), followed by a computation (x+1), followed by a write (save the result to x). The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/12dc4217f16551d6dee9cbefc23fdb5659558cda
• https://git.kernel.org/stable/c/437a310b22244d4e0b78665c3042e5d1c0f45306
• https://git.kernel.org/stable/c/614cc65032dcb0b64d23f5c5e338a8a04b12be5d
• https://git.kernel.org/stable/c/7f95f6997f4fdd17abec3200cae45420a5489350
• https://git.kernel.org/stable/c/9b5e1b93c83ee5fc9f5d7bd2d45b421bd87774a2
• https://git.kernel.org/stable/c/12dc4217f16551d6dee9cbefc23fdb5659558cda
• https://git.kernel.org/stable/c/437a310b22244d4e0b78665c3042e5d1c0f45306
• https://git.kernel.org/stable/c/614cc65032dcb0b64d23f5c5e338a8a04b12be5d
• https://git.kernel.org/stable/c/7f95f6997f4fdd17abec3200cae45420a5489350
• https://git.kernel.org/stable/c/9b5e1b93c83ee5fc9f5d7bd2d45b421bd87774a2