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

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Sat, Aug 22, 2026 at 08:28:18AM +0100, Marc Zyngier wrote:
> 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.

Ack yeah, will do!

>
> 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.

--
Cheers, Lorenzo