CVE-2026-74439iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry

Official description

In the Linux kernel, the following vulnerability has been resolved: iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry device_pasid_table_teardown() zeroes the 128-bit scalable-mode context entry with context_clear_entry() while the Present bit is still set. This creates a window where the hardware can fetch a torn entry, with some fields already zeroed while Present is still set, leading to unpredictable behavior or spurious faults. The context-cache invalidation is issued only after the entry has been zeroed, and intel_pasid_free_table() then frees the PASID directory pages, so the IOMMU can keep walking a stale Present=1 entry that points at freed memory. While x86 provides strong write ordering, the compiler may reorder the two 64-bit writes to the entry, and the hardware fetch is not guaranteed to be atomic with respect to multiple CPU writes. Commit c1e4f1dccbe9d ("iommu/vt-d: Clear Present bit before tearing down context entry") fixed this exact pattern in domain_context_clear_one() and the copied-context path, but device_pasid_table_teardown() was not converted. Align it with the "Guidance to Software for Invalidations" in the VT-d spec, Section 6.5.3.3, using the same ownership handshake as the sibling fix: clear only the Present bit, flush it to the IOMMU, perform the context-cache invalidation, and only then zero the rest of the entry.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/e9e83bcfe37dc719182500dd823c03ab57d934f0
• https://git.kernel.org/stable/c/588718101e8449605f1c7e858fecb7cfa701cdab
• https://git.kernel.org/stable/c/7fd4077dc92b91b1b844333c0a06bb9e286db10a
• https://git.kernel.org/stable/c/f46452c3df7a8d8a5addc0926e76ef19ea7da0a0