CRITICAL Introduced in 6.16
kvm arm64 VNCR Race
CVE-2026-89916
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
KernelScan AI7.8HIGH
01Description
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.
02KernelScan AI Analysis
Risk summary
A race condition in KVM arm64 nested virtualization allows a guest VM with nested virtualization enabled to trigger a stale TLB entry for VNCR translations, potentially leading to memory corruption in the host kernel. An attacker with access to a nested guest VM could exploit this to achieve host kernel code execution or denial of service. This requires ARM64 hardware with nested virtualization support (NV2) and a guest running nested virtualization.
Vulnerability analysis
A race condition in the KVM arm64 nested virtualization code can allow one virtual CPU to install a stale memory translation while another virtual CPU invalidates the same mapping. The vulnerable code checked for concurrent changes too late, after the page tables had already been walked but before the new translation was committed. The fix checks for concurrent invalidations earlier, before walking the page tables, and ensures that invalidation operations update the change counter so the translation is retried when a race is detected. A malicious guest that has nested virtualization enabled can trigger this from within a virtual machine.
Lifecycle
03Fix Versions
| Branch | Introduced | Fixed in | Patch commit |
|---|---|---|---|
| 7.2 | 6.16 | 7.2.5 | 11ee3faab4f1 |
| mainline | 6.16 | 7.3-rc1 | 2b7324f3a0c1 |
| 6.18 | 6.16 | 6.18.51 | d8580e7aa189 |