Messages in this thread Patch in this message | | | From | Alexander Graf <> | Subject | [PATCH] KVM: arm/arm64: Handle hva aging while destroying the vm | Date | Fri, 23 Jun 2017 17:21:59 +0200 |
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If we want to age an HVA while the VM is getting destroyed, we have a tiny race window during which we may end up dereferencing an invalid kvm->arch.pgd value.
CPU0 CPU1
kvm_age_hva() kvm_mmu_notifier_release() kvm_arch_flush_shadow_all() kvm_free_stage2_pgd() <grab mmu_lock> stage2_get_pmd() <wait for mmu_lock> set kvm->arch.pgd = 0 <free mmu_lock> <grab mmu_lock> stage2_get_pud() <access kvm->arch.pgd> <use incorrect value>
This patch adds a check for that case.
Signed-off-by: Alexander Graf <agraf@suse.de> --- virt/kvm/arm/mmu.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c index f2d5b6c..227931f 100644 --- a/virt/kvm/arm/mmu.c +++ b/virt/kvm/arm/mmu.c @@ -861,6 +861,10 @@ static pud_t *stage2_get_pud(struct kvm *kvm, struct kvm_mmu_memory_cache *cache pgd_t *pgd; pud_t *pud; + /* Do we clash with kvm_free_stage2_pgd()? */ + if (!kvm->arch.pgd) + return NULL; + pgd = kvm->arch.pgd + stage2_pgd_index(addr); if (WARN_ON(stage2_pgd_none(*pgd))) { if (!cache) -- 1.8.5.6
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