KVM MMU: Stale Root Fault Violates Shadow MMU Invariant
CVE-2026-64561 Published on August 4, 2026
KVM: x86: Check for invalid/obsolete root *after* making MMU pages available
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86: Check for invalid/obsolete root *after* making MMU pages available
Check for a "stale" page fault, i.e. for an invalid and/or obsolete root,
after making MMU pages available for the shadow MMU. If reclaiming shadow
pages zaps an in-use root, i.e. marks it invalid, then KVM will attempt to
map memory into an invalid root. On its own, populating an invalid root is
"fine", but because child shadow pages inherit their parent's role, any
children created during the map/fetch will be created as invalid pages,
thus violating KVM's invariant that invalid pages are never on the list of
active MMU pages.
Note, the underlying flaw has existed since KVM first started tracking
invalid roots in 2008 (commit 2e53d63acba7, "KVM: MMU: ignore zapped root
pagetables"), but the true badness only came along in 2020 (Linux 5.9)
with the invariant that invalid shadow pages can't be on the list of
active pages.
Note #2, inheriting role.invalid when creating child shadow pages is also
far from ideal; that flaw will be addressed separately.
Products Associated with CVE-2026-64561
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Affected Versions
Linux:- Version f95eec9bed76d42194c23153cb1cc8f186bf91cb and below 35e77467610c4a37cb0ff54ee56b85f73b1f5700 is affected.
- Version f95eec9bed76d42194c23153cb1cc8f186bf91cb and below 0026dbb7de8ea76e97d6edf42fc3cc084564e2bf is affected.
- Version f95eec9bed76d42194c23153cb1cc8f186bf91cb and below f3477a6a4164f15287444eda685b5f6405dbd1e5 is affected.
- Version f95eec9bed76d42194c23153cb1cc8f186bf91cb and below bce0d3c26e2c761a4bf43c8949f333fc7374eb2d is affected.
- Version f95eec9bed76d42194c23153cb1cc8f186bf91cb and below 2abd5287f08319fa35764566b15c6e22cb1068db is affected.
- Version 5.9 is affected.
- Before 5.9 is unaffected.
- Version 6.6.148, <= 6.6.* is unaffected.
- Version 6.12.101, <= 6.12.* is unaffected.
- Version 6.18.42, <= 6.18.* is unaffected.
- Version 7.1.6, <= 7.1.* is unaffected.
- Version 7.2-rc5, <= * is unaffected.