iommu/vt-d: Clear Present bit before tearing down PASID entry

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Summary

CVECVE-2026-45894
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-27 14:17:03 UTC
Updated2026-05-27 14:48:31 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: iommu/vt-d: Clear Present bit before tearing down PASID entry The Intel VT-d Scalable Mode PASID table entry consists of 512 bits (64 bytes). When tearing down an entry, the current implementation zeros the entire 64-byte structure immediately using multiple 64-bit writes. Since the IOMMU hardware may fetch these 64 bytes using multiple internal transactions (e.g., four 128-bit bursts), updating or zeroing the entire entry while it is active (P=1) risks a "torn" read. If a hardware fetch occurs simultaneously with the CPU zeroing the entry, the hardware could observe an inconsistent state, leading to unpredictable behavior or spurious faults. Follow the "Guidance to Software for Invalidations" in the VT-d spec (Section 6.5.3.3) by implementing the recommended ownership handshake: 1. Clear only the 'Present' (P) bit of the PASID entry. 2. Use a dma_wmb() to ensure the cleared bit is visible to hardware before proceeding. 3. Execute the required invalidation sequence (PASID cache, IOTLB, and Device-TLB flush) to ensure the hardware has released all cached references. 4. Only after the flushes are complete, zero out the remaining fields of the PASID entry. Also, add a dma_wmb() in pasid_set_present() to ensure that all other fields of the PASID entry are visible to the hardware before the Present bit is set.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 0bbeb01a4fafbf8422e5c8882d461d6ac4f71e15 a84d30e8d2bacd21782a6481158b7c9c552f4868 git Not specified
CNA Linux Linux affected 0bbeb01a4fafbf8422e5c8882d461d6ac4f71e15 821807c167b7b48a41b95b6607c6b9f97600f7d9 git Not specified
CNA Linux Linux affected 0bbeb01a4fafbf8422e5c8882d461d6ac4f71e15 949d71666e9dd19f21e7b4b53a88cd2c5b902858 git Not specified
CNA Linux Linux affected 0bbeb01a4fafbf8422e5c8882d461d6ac4f71e15 75ed00055c059dedc47b5daaaa2f8a7a019138ff git Not specified
CNA Linux Linux affected 5.0 Not specified
CNA Linux Linux unaffected 5.0 semver Not specified
CNA Linux Linux unaffected 6.12.75 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.14 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.4 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/821807c167b7b48a41b95b6607c6b9f97600f7d9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a84d30e8d2bacd21782a6481158b7c9c552f4868 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/75ed00055c059dedc47b5daaaa2f8a7a019138ff 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/949d71666e9dd19f21e7b4b53a88cd2c5b902858 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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