KVM: nSVM: Clear EVENTINJ fields in vmcb12 on nested #VMEXIT

commit 69b721a upstream.

According to the APM, from the reference of the VMRUN instruction:

  Upon #VMEXIT, the processor performs the following actions in order to
  return to the host execution context:

  ...

  clear EVENTINJ field in VMCB

KVM already syncs EVENTINJ fields from vmcb02 to cached vmcb12 on every
L2->L0  #VMEXIT. Since these fields are zeroed by the CPU on #VMEXIT, they
will mostly be zeroed in vmcb12 on nested #VMEXIT by nested_svm_vmexit().

However, this is not the case when:

  1. Consistency checks fail, as nested_svm_vmexit() is not called.
  2. Entering guest mode fails before L2 runs (e.g. due to failed load of
     CR3).

(2) was broken by commit 2d8a42b ("KVM: nSVM: synchronize VMCB
controls updated by the processor on every vmexit"), as prior to that
nested_svm_vmexit() always zeroed EVENTINJ fields.

Explicitly clear the fields in all nested #VMEXIT code paths.

Fixes: 3d6368e ("KVM: SVM: Add VMRUN handler")
Fixes: 2d8a42b ("KVM: nSVM: synchronize VMCB controls updated by the processor on every vmexit")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260303003421.2185681-12-yosry@kernel.org
[sean: massage changelog formatting]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Yosry Ahmed

arch/x86/kvm/svm/nested.c

@@ -884,6 +884,8 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 		vmcb12->control.exit_code_hi = -1u;
 		vmcb12->control.exit_info_1  = 0;
 		vmcb12->control.exit_info_2  = 0;
+		vmcb12->control.event_inj = 0;
+		vmcb12->control.event_inj_err = 0;
 		svm_set_gif(svm, false);
 		goto out;
 	}
@@ -1025,9 +1027,9 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	if (guest_can_use(vcpu, X86_FEATURE_NRIPS))
 		vmcb12->control.next_rip  = vmcb02->control.next_rip;
 
+	vmcb12->control.event_inj	  = 0;
+	vmcb12->control.event_inj_err	  = 0;
 	vmcb12->control.int_ctl           = svm->nested.ctl.int_ctl;
-	vmcb12->control.event_inj         = svm->nested.ctl.event_inj;
-	vmcb12->control.event_inj_err     = svm->nested.ctl.event_inj_err;
 
 	if (!kvm_pause_in_guest(vcpu->kvm)) {
 		vmcb01->control.pause_filter_count = vmcb02->control.pause_filter_count;