KVM: x86/mmu: Consume the locked rmap value in the lockless rmap walk

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89928
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 11:17:02 UTC
Updated2026-10-19 09:18:38 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Consume the locked rmap value in the lockless rmap walk __kvm_rmap_lock() deliberately elides the rmap lock when it observes an empty rmap. In that case kvm_rmap_lock_readonly() also re-enables preemption and returns zero, so the caller holds neither the rmap lock nor a preemption reference. The elision documents the invariant it relies on: * Elide the lock if the rmap is empty, as lockless walkers (read-only * mode) don't need to (and can't) walk an empty rmap, nor can they add * entries to the rmap. I.e. the only paths that process empty rmaps * do so while holding mmu_lock for write, and are mutually exclusive. kvm_rmap_age_gfn_range() ignores the returned value and unconditionally enters for_each_rmap_spte_lockless(). The iterator started with rmap_get_first(), which re-reads rmap_head->val rather than using the value returned by the lock. If a writer populates the rmap between the lock's read and the iterator's re-read, the aging path walks the newly installed rmap without holding its lock. For a KVM_RMAP_MANY rmap this leaves the walker following a pte_list_desc chain that it never locked. A writer holding mmu_lock for write may free that chain (e.g. kvm_zap_all_rmap_sptes() on the recycle path, or any rmap zap) via kmem_cache_free() while the walk is in progress, giving a slab use-after-free. Nothing serialises the two: the aging path runs without mmu_lock when CONFIG_KVM_MMU_LOCKLESS_AGING=y, and the rmap lock that would otherwise exclude the writer was elided. Because the empty path re-enables preemption, the interval between the two reads can span an arbitrary scheduling delay. Fix the class of bug by having the lockless walk consume the value returned by the lock instead of re-reading the rmap. Split rmap_get_first() into __rmap_get_first(), which starts an iterator from an already-read rmap value, and make for_each_rmap_spte_lockless() take that value and call __rmap_get_first() directly. kvm_rmap_age_gfn_range() passes the value returned by kvm_rmap_lock_readonly(): when the lock was elided the value is zero, __rmap_get_first() returns NULL, and the walk is skipped. No lockless walker re-reads the rmap, so the lock-elision invariant cannot be violated, and no lock()-without-paired-unlock() path is added to the aging code.

Risk And Classification

Primary CVSS: v3.1 8.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary8.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
3.1CNADECLARED8.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected af3b6a9eba48419732b07a0472db7160282f0f39 41debfc98526c0a95c41a62435aca0a70340a26d git Not specified
CNA Linux Linux affected af3b6a9eba48419732b07a0472db7160282f0f39 8edb3c09e43f7cd8a5dfd291c6e0fc9c74d4621d git Not specified
CNA Linux Linux affected af3b6a9eba48419732b07a0472db7160282f0f39 e428f9779a43737d830111238816f1928b07aefb git Not specified
CNA Linux Linux affected 6.15 Not specified
CNA Linux Linux unaffected 6.15 semver Not specified
CNA Linux Linux unaffected 6.18.51 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.5 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/e428f9779a43737d830111238816f1928b07aefb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/41debfc98526c0a95c41a62435aca0a70340a26d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/8edb3c09e43f7cd8a5dfd291c6e0fc9c74d4621d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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