KVM: SVM: fix cr8 intercept window

We always disable cr8 intercept in its handler, but only re-enable it
if handling KVM_REQ_EVENT, so there can be a window where we do not
intercept cr8 writes, which allows an interrupt to disrupt a higher
priority task.

Fix this by disabling intercepts in the same function that re-enables
them when needed. This fixes BSOD in Windows 2008.

Cc: <stable@vger.kernel.org>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index e81df8fce027..2de1bc09a8d4 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3002,10 +3002,8 @@ static int cr8_write_interception(struct vcpu_svm *svm)
         u8 cr8_prev = kvm_get_cr8(&svm->vcpu);
         /* instruction emulation calls kvm_set_cr8() */
         r = cr_interception(svm);
-        if (irqchip_in_kernel(svm->vcpu.kvm)) {
-                clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
+        if (irqchip_in_kernel(svm->vcpu.kvm))
                 return r;
-        }
         if (cr8_prev <= kvm_get_cr8(&svm->vcpu))
                 return r;
         kvm_run->exit_reason = KVM_EXIT_SET_TPR;
@@ -3567,6 +3565,8 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
         if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
                 return;
 
+        clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
+
         if (irr == -1)
                 return;