6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Lorenzo Stoakes (ARM) commit 4c74e233cdedd11592775fae2a6243e67ca3f891 upstream. 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. Fixes: 7270cc9157f4 ("KVM: arm64: nv: Handle VNCR_EL2 invalidation from MMU notifiers") Cc: stable@vger.kernel.org Reviewed-by: Marc Zyngier Signed-off-by: Lorenzo Stoakes (ARM) Tested-by: Jonathan Davies Link: https://patch.msgid.link/20260901-kvm-arm-nested-virt-fix-v3-2-b154676f7e4c@kernel.org Signed-off-by: Oliver Upton Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kvm/nested.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) --- a/arch/arm64/kvm/nested.c +++ b/arch/arm64/kvm/nested.c @@ -1129,6 +1129,17 @@ void kvm_handle_s1e2_tlbi(struct kvm_vcp invalidate_vncr_va(vcpu->kvm, &scope); } +static void kvm_invalidate_vncr_ipa_all(struct kvm *kvm) +{ + struct kvm_pgtable *pgt = kvm->arch.mmu.pgt; + + lockdep_assert_held_write(&kvm->mmu_lock); + + /* if the mmu lock was dropped, pgt teardown may have raced. */ + if (pgt) + kvm_invalidate_vncr_ipa(kvm, 0, BIT(pgt->ia_bits)); +} + void kvm_nested_s2_wp(struct kvm *kvm) { int i; @@ -1142,7 +1153,7 @@ 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) @@ -1158,7 +1169,7 @@ void kvm_nested_s2_unmap(struct kvm *kvm 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)