CVE-2026-43486

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

arm64: contpte: fix set_access_flags() no-op check for SMMU/ATS faults

contpte_ptep_set_access_flags() compared the gathered ptep_get() value against the requested entry to detect no-ops. ptep_get() ORs AF/dirty from all sub-PTEs in the CONT block, so a dirty sibling can make the target appear already-dirty. When the gathered value matches entry, the function returns 0 even though the target sub-PTE still has PTE_RDONLY set in hardware.

For a CPU with FEAT_HAFDBS this gathered view is fine, since hardware may set AF/dirty on any sub-PTE and CPU TLB behavior is effectively gathered across the CONT range. But page-table walkers that evaluate each descriptor individually (e.g. a CPU without DBM support, or an SMMU without HTTU, or with HA/HD disabled in CD.TCR) can keep faulting on the unchanged target sub-PTE, causing an infinite fault loop.

Gathering can therefore cause false no-ops when only a sibling has been updated:

• write faults: target still has PTE_RDONLY (needs PTE_RDONLY cleared)
• read faults: target still lacks PTE_AF

Fix by checking each sub-PTE against the requested AF/dirty/write state (the same bits consumed by __ptep_set_access_flags()), using raw per-PTE values rather than the gathered ptep_get() view, before returning no-op. Keep using the raw target PTE for the write-bit unfold decision.

Per Arm ARM (DDI 0487) D8.7.1 (The Contiguous bit), any sub-PTE in a CONT range may become the effective cached translation and software must maintain consistent attributes across the range.

Weakness

The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.

Affected Software

References

• https://git.kernel.org/stable/c/05d239f2c95e66e27e7fb4e99ee07eb56e3e34b0
• https://git.kernel.org/stable/c/09d620555e59768776090073a2c59d2bc8506eb3
• https://git.kernel.org/stable/c/6f92a7a8b48a523f910ef25dd83808710724f59b
• https://git.kernel.org/stable/c/97c5550b763171dbef61e6239cab372b9f9cd4a2