---
id: "CVE-2026-98467"
kind: "vulnerability"
aliases: ["CVE-2026-98467"]
title: "Linux kernel KVM arm64: null pointer dereference during nested guest teardown"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["arm64", "kvm", "linux-kernel", "nested-virtualization", "runtime"]
not_affected_if: ["no-nested-virtualization", "x86-host"]
published_at: "2026-10-18T16:16:57+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:27:10+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98467", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel KVM arm64: null pointer dereference during nested guest teardown

A race in the arm64 KVM nested virtualization code can set the stage 2 page table pointer to NULL while an unmap or write-protect operation is still using it, causing a kernel null pointer dereference. The sources describe a crash on the host kernel, and the text does not say whether an attacker can trigger it from a guest.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `uname -r` and compare the kernel version against the fixed kernel releases in the NVD entry.
- Check whether the host uses arm64 KVM with nested virtualization enabled (unknown from the sources; look for `nv` options on KVM hosts).

## Fix

- Update the Linux kernel to a release that includes the upstream fix (the exact version is unknown from the sources; check the NVD entry or the distribution advisory).

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98467

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

KVM: arm64: nv: Fix null ptr deref on nested wp/unmap, teardown race

Commit 7270cc9157f4 ("KVM: arm64: nv: Handle VNCR_EL2 invalidation from MMU
notifiers") introduced VNCR_EL2 invalidation in both kvm_nested_s2_unmap()
and kvm_nested_s2_wp().

However at the point of this being performed concurrent stage 2 teardown of
a nested guest can cause kvm->arch.mmu.pgt to be set to NULL.

This happens in kvm_flush_shadow_all() -> kvm_arch_flush_shadow_all() ->
kvm_free_stage2_pgd() and is performed under the kvm->mmu_lock.

Commit ec14c272408a ("KVM: arm64: nv: Unmap/flush shadow stage 2 page
tables") introduced the teardown of the entire nested MMU range, which then
invokes stage2_apply_range() with resched=true:

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()

This means that stage2_apply_range() can drop the kvm->mmu_lock and thus
concurrent progress can be made in lockstep with
kvm_arch_flush_shadow_all().

If kvm_arch_flush_shadow_all() advances ahead of stage2_apply_range() and
completes its operation it guarantees a NULL pointer deref.

Since kvm_free_stage2_pgd() is performed under the kvm->mmu_lock this will
either be observed NULL or not and serialised against
kvm_free_stage2_pgd().

Resolve the issue by abstracting the invalidation to a new function,
kvm_invalidate_vncr_ipa_all(), and check that the pgt is non-NULL before
dereferencing it.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_