CVE-2026-45945

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

iommu/vt-d: Fix race condition during PASID entry replacement

The Intel VT-d PASID table entry is 512 bits (64 bytes). When replacing an active PASID entry (e.g., during domain replacement), the current implementation calculates a new entry on the stack and copies it to the table using a single structure assignment.

    struct pasid_entry *pte, new_pte;

    pte = intel_pasid_get_entry(dev, pasid);
    pasid_pte_config_first_level(iommu, &new_pte, ...);
    *pte = new_pte;

Because the hardware may fetch the 512-bit PASID entry in multiple 128-bit chunks, updating the entire entry while it is active (Present bit set) risks a torn read. In this scenario, the IOMMU hardware could observe an inconsistent state — partially new data and partially old data — leading to unpredictable behavior or spurious faults.

Fix this by removing the unsafe replace helpers and following the clear-then-update flow, which ensures the Present bit is cleared and the required invalidation handshake is completed before the new configuration is applied.

Weakness

The product contains a concurrent code sequence that 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 operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it 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. 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/66a7aff480a82b8642b3991fed5fdc9780022157
• https://git.kernel.org/stable/c/c3b1edea3791fa91ab7032faa90355913ad9451b