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[PATCH] KVM: x86: fix wbinvd_dirty_mask use-after-free

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vcpu->arch.wbinvd_dirty_mask may still be used after freeing it,
corrupting memory. For example, the following call trace may set a bit
in an already freed cpu mask:
    kvm_arch_vcpu_load
    vcpu_load
    vmx_free_vcpu_nested
    vmx_free_vcpu
    kvm_arch_vcpu_free

Fix this by deferring freeing of wbinvd_dirty_mask.

Cc: stable@vger.kernel.org
Signed-off-by: Ido Yariv <ido@wizery.com>
---
 arch/x86/kvm/x86.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c633de..9ec8c1d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7410,10 +7410,12 @@ void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 
 void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
 {
+	void *wbinvd_dirty_mask = vcpu->arch.wbinvd_dirty_mask;
+
 	kvmclock_reset(vcpu);
 
-	free_cpumask_var(vcpu->arch.wbinvd_dirty_mask);
 	kvm_x86_ops->vcpu_free(vcpu);
+	free_cpumask_var(wbinvd_dirty_mask);
 }
 
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
-- 
2.5.5

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[PATCH] KVM: x86: fix wbinvd_dirty_mask use-after-free Ido Yariv <ido@wizery.com> - 2016-10-21 18:50 +0200
  Re: [PATCH] KVM: x86: fix wbinvd_dirty_mask use-after-free Paolo Bonzini <pbonzini@redhat.com> - 2016-10-24 16:20 +0200
  Re: [PATCH] KVM: x86: fix wbinvd_dirty_mask use-after-free Radim Krčmář <rkrcmar@redhat.com> - 2016-10-24 17:30 +0200

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