KVM: x86: Fix shadow paging use-after-free due to unexpected GFN

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Summary

CVECVE-2026-46113
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-28 10:16:26 UTC
Updated2026-05-28 13:44:01 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: KVM: x86: Fix shadow paging use-after-free due to unexpected GFN The shadow MMU computes GFNs for direct shadow pages using sp->gfn plus the SPTE index. This assumption breaks for shadow paging if the guest page tables are modified between VM entries (similar to commit aad885e77496, "KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE", 2026-03-27). The flow is as follows: - a PDE is installed for a 2MB mapping, and a page in that area is accessed. KVM creates a kvm_mmu_page consisting of 512 4KB pages; the kvm_mmu_page is marked by FNAME(fetch) as direct-mapped because the guest's mapping is a huge page (and thus contiguous). - the PDE mapping is changed from outside the guest. - the guest accesses another page in the same 2MB area. KVM installs a new leaf SPTE and rmap entry; the SPTE uses the "correct" GFN (i.e. based on the new mapping, as changed in the previous step) but that GFN is outside of the [sp->gfn, sp->gfn + 511] range; therefore the rmap entry cannot be found and removed when the kvm_mmu_page is zapped. - the memslot that covers the first 2MB mapping is deleted, and the kvm_mmu_page for the now-invalid GPA is zapped. However, rmap_remove() only looks at the [sp->gfn, sp->gfn + 511] range established in step 1, and fails to find the rmap entry that was recorded by step 3. - any operation that causes an rmap walk for the same page accessed by step 3 then walks a stale rmap and dereferences a freed kvm_mmu_page. This includes dirty logging or MMU notifier invalidations (e.g., from MADV_DONTNEED). The underlying issue is that KVM's walking of shadow PTEs assumes that if a SPTE is present when KVM wants to install a non-leaf SPTE, then the existing kvm_mmu_page must be for the correct gfn. Because the only way for the gfn to be wrong is if KVM messed up and failed to zap a SPTE... which shouldn't happen, but *actually* only happens in response to a guest write. That bug dates back literally forever, as even the first version of KVM assumes that the GFN matches and walks into the "wrong" shadow page. However, that was only an imprecision until 2032a93d66fa ("KVM: MMU: Don't allocate gfns page for direct mmu pages") came along. Fix it by checking for a target gfn mismatch and zapping the existing SPTE. That way the old SP and rmap entries are gone, KVM installs the rmap in the right location, and everyone is happy.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 6aa8b732ca01c3d7a54e93f4d701b8aabbe60fb7 488e386484ec8c0e558be6e156edf34ed9f4d5c8 git Not specified
CNA Linux Linux affected 6aa8b732ca01c3d7a54e93f4d701b8aabbe60fb7 06c19c967b845b63172601fe459667d973b7e6b7 git Not specified
CNA Linux Linux affected 6aa8b732ca01c3d7a54e93f4d701b8aabbe60fb7 738ec97b1855df6c08fe2369f798fa0b972e556b git Not specified
CNA Linux Linux affected 6aa8b732ca01c3d7a54e93f4d701b8aabbe60fb7 14d1e55dfd2cf4711bff164a6aaaddb783552134 git Not specified
CNA Linux Linux affected 6aa8b732ca01c3d7a54e93f4d701b8aabbe60fb7 0cb2af2ea66ad8ff195c156ea690f11216285bdf git Not specified
CNA Linux Linux affected 2.6.20 Not specified
CNA Linux Linux unaffected 2.6.20 semver Not specified
CNA Linux Linux unaffected 6.6.140 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.88 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.30 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.7 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1-rc3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/488e386484ec8c0e558be6e156edf34ed9f4d5c8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/738ec97b1855df6c08fe2369f798fa0b972e556b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/06c19c967b845b63172601fe459667d973b7e6b7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/14d1e55dfd2cf4711bff164a6aaaddb783552134 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/0cb2af2ea66ad8ff195c156ea690f11216285bdf 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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