KVM: Reject wrapped offset in kvm_reset_dirty_gfn()

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Summary

CVECVE-2026-52969
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-24 17:17:07 UTC
Updated2026-06-24 17:17:07 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: KVM: Reject wrapped offset in kvm_reset_dirty_gfn() kvm_reset_dirty_gfn() guards the gfn range with if (!memslot || (offset + __fls(mask)) >= memslot->npages) return; but offset is u64 and the addition is unchecked. The check can be silently bypassed by a u64 wrap. The dirty ring backing those entries is MAP_SHARED at KVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the slot and offset fields of any entry between when the kernel pushes them and when KVM_RESET_DIRTY_RINGS consumes them. On reset, kvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds them straight back into this check; only the flags handshake is treated as the handover, the slot/offset payload is taken on trust. Crafting two entries entry[i].offset = 0xffffffffffffffc1 entry[i+1].offset = 0 makes the coalescing loop in kvm_dirty_ring_reset() compute delta = (s64)(0 - 0xffffffffffffffc1) = 63 which falls in [0, BITS_PER_LONG), so it folds entry[i+1] into the existing mask by setting bit 63. The trailing kvm_reset_dirty_gfn() call then sees offset = 0xffffffffffffffc1 and __fls(mask) = 63; the sum is 0 in u64 and the bounds check passes. That offset propagates into kvm_arch_mmu_enable_log_dirty_pt_masked() unchanged. On the legacy MMU path -- kvm_memslots_have_rmaps() == true, i.e. shadow paging, any VM that has allocated shadow roots, or a write-tracked slot -- it reaches gfn_to_rmap(), which indexes slot->arch.rmap[0][] with a near-U64_MAX gfn. That is an out-of-bounds load of a kvm_rmap_head, followed by a conditional clear of PT_WRITABLE_MASK in whatever the loaded pointer points at. The path is reachable from any process holding /dev/kvm. Range-check offset on its own first, so the addition cannot wrap. memslot->npages is bounded well below U64_MAX, so once offset < npages holds, offset + __fls(mask) (with __fls(mask) < BITS_PER_LONG) stays in range.

Risk And Classification

EPSS: 0.001890000 probability, percentile 0.086920000 (date 2026-06-25)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected fb04a1eddb1a65b6588a021bdc132270d5ae48bb 74f1a22f7a80f03d28ad8551a2d25d563433addf git Not specified
CNA Linux Linux affected fb04a1eddb1a65b6588a021bdc132270d5ae48bb 0eb281eb95b2d4eea4db1da5fe91023aecc97095 git Not specified
CNA Linux Linux affected fb04a1eddb1a65b6588a021bdc132270d5ae48bb 01b71b930f15728aa8599478a7ce90c19dcd9fc2 git Not specified
CNA Linux Linux affected fb04a1eddb1a65b6588a021bdc132270d5ae48bb b315b033a877b1ee6d827810b5d7bb4392ffcf8d git Not specified
CNA Linux Linux affected fb04a1eddb1a65b6588a021bdc132270d5ae48bb 0d419c23bb11b5c9664de777c47c1f04a235882d git Not specified
CNA Linux Linux affected fb04a1eddb1a65b6588a021bdc132270d5ae48bb ecf9b3ea7847fe14f34b8c41f00de1eb95c747da git Not specified
CNA Linux Linux affected fb04a1eddb1a65b6588a021bdc132270d5ae48bb 577a8d3bae0531f0e5ccfac919cd8192f920a804 git Not specified
CNA Linux Linux affected 5.11 Not specified
CNA Linux Linux unaffected 5.11 semver Not specified
CNA Linux Linux unaffected 5.15.209 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.175 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.141 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.91 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.33 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.10 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/ecf9b3ea7847fe14f34b8c41f00de1eb95c747da 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/01b71b930f15728aa8599478a7ce90c19dcd9fc2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/0eb281eb95b2d4eea4db1da5fe91023aecc97095 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/577a8d3bae0531f0e5ccfac919cd8192f920a804 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b315b033a877b1ee6d827810b5d7bb4392ffcf8d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/0d419c23bb11b5c9664de777c47c1f04a235882d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/74f1a22f7a80f03d28ad8551a2d25d563433addf 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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