Bug 2535218 (CVE-2026-89916)

Summary: CVE-2026-89916 kernel: KVM: arm64: Make VNCR invalidation participate in MMU invalidation retry
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's KVM (Kernel-based Virtual Machine) for arm64 architectures. This vulnerability involves a race condition during Translation Lookaside Buffer (TLB) invalidation. Specifically, one virtual CPU (vcpu) could attempt to insert a TLB entry for a page that another vcpu has concurrently marked as invalid. This could lead to incorrect memory translations, potentially causing system instability or unexpected behavior within the virtualized environment.
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Description OSIDB Bzimport 2026-09-16 11:36:31 UTC 
In the Linux kernel, the following vulnerability has been resolved:

KVM: arm64: Make VNCR invalidation participate in MMU invalidation retry

A VNCR TLB invalidation can occur on one vcpu while another vcpu is
faulting in this same page. Without correctly handling this, we can
end up with the following scenario:

- vcpu A walks the PTs to translate VNCR
- before vcpu A is able to grab the MMU lock to insert the TLB,
  vcpu B updates the S1 PTs with an invalid entry, and issues
  a TLBI S1E2 for this VA
- vcpu A inserts the TLB for something that is now invalid

This isn't a new problem, and we manage S2 by having the MMU notifier
to bump up mmu_invalidate_seq on invalidation so that the fault can be
replayed.

We can perform something similar here, and extend invalidate_vncr_va() to
update the same counter, clearly indicating that the context has
changed under our feet. This is safe as the invalidation always happen
while holding the MMU lock for write, and that we sample the sequence
number before walking S1.
Comment 1 Keith Grant 2026-09-16 14:45:02 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89916.mbox