CVE-2026-98468
Description
In the Linux kernel, the following vulnerability has been resolved:
KVM: arm64: Fix spurious warning for benign stage 2 teardown race
kvmtool was used to establish an L1 guest with 8 CPUs and 8 GiB of RAM, an
L2 guest with 4 CPUs and 4 GiB of RAM and an L3 guest with 2 CPUs and 2 GiB
of RAM, all of which was then exited.
Under memory pressure in the L0 host warnings were observed due to
migration triggered by compaction:
WARNING: arch/arm64/kvm/mmu.c:336 at __unmap_stage2_range+0x64/0x80,
CPU#5: kcompactd0/66
Which was, in turn, triggered by an MMU notifier for the host invalidation:
mmu_notifier_invalidate_range_start()
-> ... -> kvm_mmu_notifier_invalidate_range_start()
-> kvm_mmu_unmap_gfn_range()
-> kvm_unmap_gfn_range()
-> kvm_nested_s2_unmap()
-> kvm_stage2_unmap_range()
-> __unmap_stage2_range()
-> stage2_apply_range()
<- -EINVAL, triggering a WARN_ON()
Racing with L0's teardown of stage 2 page tables:
exit_mm()
-> mmput()
-> __mmput()
-> exit_mmap()
-> mmu_notifier_release()
-> ... -> kvm_mmu_notifier_release()
-> kvm_flush_shadow_all()
-> kvm_arch_flush_shadow_all()
-> kvm_free_stage2_pgd()
-> [ acquire kvm->mmu_lock for write ]
-> mmu->pgt = NULL [ among other tasks ]
-> [ release kvm->mmu_lock for write ]
It turns out there is a benign race resulting in a spurious warning:
Thread A - notify: migration | Thread B - notify: release
-------------------------------|---------------------------------
< kvm->mmu_lock held > |
stage2_apply_range() |
get mmu->pgt, check !NULL |
... | kvm_arch_flush_shadow_all()
cond_resched_rwlock_write(); | < contend, sleep kvm->mmu_lock >
< drop kvm->mmu_lock > | < acquire kvm->mmu_lock>
| ...
| kvm_free_stage2_pgd()
| mmu->pgt = NULL
| < invalidate MMU >
| ...
| < release kvm->mmu_lock >
[ scheduled ] |
stage2_apply_range() |
< loop to next > |
get, mmu->pgt, check !NULL |
is NULL, return -EINVAL |
__unmap_stage2_range() |
WARN_ON(-EINVAL) <--- entirely spurious - the race was handled
correctly.
Fix the spurious warning by updating stage2_apply_range() to no longer
treat concurrent PGT teardown on lock release as an error - whether the
walker is tearing down page tables or doing something else this is a
legitimate reason to abort the operation without error.
This keeps the warning in place for all other circumstances.
In practice only __unmap_stage2_range() actually does anything with the
error so this only impacts that.
EPSS (Exploit Prediction Scoring System)
EPSS (Exploit Prediction Scoring System)
Prevede la probabilità di sfruttamento basata su intelligence sulle minacce e sulle caratteristiche della vulnerabilità.