iommu/amd: Wait for completion instead of returning early in iommu_completion_wait()

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Summary

CVECVE-2026-68329
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-10 13:20:23 UTC
Updated2026-08-10 13:20:23 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: iommu/amd: Wait for completion instead of returning early in iommu_completion_wait() need_sync is a per-IOMMU flag shared by all domains and devices behind that IOMMU. It is set whenever a command is queued with sync == true and cleared when a completion-wait (CWAIT) command is queued. However, a cleared need_sync only means that a covering CWAIT has been queued, not that all previously queued commands have actually completed in hardware. iommu_completion_wait() read need_sync locklessly and returned early when it was false. This breaks the "block until all previously queued commands have completed" contract in a multi-CPU scenario: CPU2: queue inv-B => need_sync = true CPU1: queue CWAIT(N); need_sync = false; then wait_on_sem(N) CPU2: read need_sync == false => return 0 (no wait!) CPU2 returns without waiting for any sequence number even though its inv-B may not have completed yet (CWAIT(N), queued after inv-B, has not been signaled). CPU2 then proceeds to, for example, free page-table pages while the IOMMU can still walk stale translations, opening a use-after-free window. This is a logical race in the meaning of the flag, not a memory-visibility issue, so barriers alone do not help. Fix it without losing the optimization of avoiding redundant CWAIT commands: take iommu->lock before testing need_sync, and when it is false do not return early but wait for the last allocated sequence number (cmd_sem_val). Since need_sync == false implies no sync command was queued after the last CWAIT, that CWAIT is FIFO-ordered after every not-yet-completed command, so waiting for its sequence number guarantees all prior commands (possibly queued by another CPU) have completed. The common path with pending work is unchanged and no extra hardware command is issued.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 815b33fdc279d34ab40a8bfe1866623a4cc5669b ab7faf5a172ebfdc423ebb3eea4d472740de82f9 git Not specified
CNA Linux Linux affected 815b33fdc279d34ab40a8bfe1866623a4cc5669b 93494bd446396c257fb589f59894577e96e406e2 git Not specified
CNA Linux Linux affected 815b33fdc279d34ab40a8bfe1866623a4cc5669b d053eb7e09e10cbdca3fca8b35c1017d438091b2 git Not specified
CNA Linux Linux affected 815b33fdc279d34ab40a8bfe1866623a4cc5669b 02f8cefa2ad95ea3754f0cfd6fbae7f866202ccb git Not specified
CNA Linux Linux affected 815b33fdc279d34ab40a8bfe1866623a4cc5669b 1e75a8255f11c81fb07e81e5029cfd75804350a0 git Not specified
CNA Linux Linux affected 3.0 Not specified
CNA Linux Linux unaffected 3.0 semver Not specified
CNA Linux Linux unaffected 6.6.148 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.101 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.42 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.6 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc5 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/93494bd446396c257fb589f59894577e96e406e2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d053eb7e09e10cbdca3fca8b35c1017d438091b2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ab7faf5a172ebfdc423ebb3eea4d472740de82f9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/02f8cefa2ad95ea3754f0cfd6fbae7f866202ccb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1e75a8255f11c81fb07e81e5029cfd75804350a0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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