CVE-2026-74439
Low risk· EPSS 5%Exploitation Probability (EPSS)
Low risk5th percentile - higher than 5% of all known CVEs
Summary
In the Linux kernel's iommu/vt-d subsystem, the Present bit is not cleared before tearing down a scalable-mode context entry, creating a window where hardware can fetch a torn entry, leading to unpredictable behavior or spurious faults. The issue affects device_pasid_table_teardown(), which was not aligned with a previous fix.
Risk Assessment
The risk includes potential hardware faults, system instability, or access to freed memory, which could lead to crashes or data integrity issues.
Recommendation
Apply the kernel patch that clears the Present bit before zeroing the entry, following the VT-d specification guidelines. Update the kernel to a version containing this fix.
Original NVD description (English source)
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.