Re: [PATCH 2/2] KVM: arm64: nv: Fix null ptr deref in kvm_nested_s2_unmap() on S2 teardown

[Marc Zyngier <maz@kernel.org>]

On Thu, 13 Aug 2026 16:56:02 +0100,
"Lorenzo Stoakes (ARM)" <ljs@kernel.org> wrote:
> 
> On Wed, Aug 12, 2026 at 02:01:01PM +0000, sashiko-bot@kernel.org wrote:
> > Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
> >
> > Pre-existing issues:
> > - [Critical] Use-After-Free on `kvm->arch.nested_mmus` array due to concurrent teardown.
> 
> Addressed by Marc's changes + discussed over there.
> 
> > - [Critical] Incomplete Fix: `kvm_nested_s2_wp()` is vulnerable to the same NULL pointer dereference and UAF.
> 
> OK interesting!

Will you respin this series with kvm_nested_s2_wp() fixed in a similar
way? Something like below.

Thanks,

	M.

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 00580ba6e8ba0..ebc4f4dc47836 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -1262,6 +1262,14 @@ void kvm_handle_s1e2_tlbi(struct kvm_vcpu *vcpu, u32 inst, u64 val)
 	invalidate_vncr_va(vcpu->kvm, &scope);
 }
 
+static void kvm_invalidate_vncr_ipa_all(struct kvm *kvm)
+{
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
+	if (kvm->arch.mmu.pgt)
+		kvm_invalidate_vncr_ipa(kvm, 0, BIT(kvm->arch.mmu.pgt->ia_bits));
+}
+
 void kvm_nested_s2_wp(struct kvm *kvm)
 {
 	int i;
@@ -1278,7 +1286,7 @@ void kvm_nested_s2_wp(struct kvm *kvm)
 			kvm_stage2_wp_range(mmu, 0, kvm_phys_size(mmu));
 	}
 
-	kvm_invalidate_vncr_ipa(kvm, 0, BIT(kvm->arch.mmu.pgt->ia_bits));
+	kvm_invalidate_vncr_ipa_all(kvm);
 }
 
 void kvm_nested_s2_unmap(struct kvm *kvm, bool may_block)
@@ -1297,7 +1305,7 @@ void kvm_nested_s2_unmap(struct kvm *kvm, bool may_block)
 			kvm_stage2_unmap_range(mmu, 0, kvm_phys_size(mmu), may_block);
 	}
 
-	kvm_invalidate_vncr_ipa(kvm, 0, BIT(kvm->arch.mmu.pgt->ia_bits));
+	kvm_invalidate_vncr_ipa_all(kvm);
 }
 
 void kvm_nested_s2_flush(struct kvm *kvm)

-- 
Without deviation from the norm, progress is not possible.