[PATCH] KVM: VMX: check nested state and CR4.VMXE against SMM

[Paolo Bonzini]

VMX cannot be enabled under SMM, check it when CR4 is set and when nested
virtualization state is restored.

This should fix some WARNs reported by syzkaller, mostly around
alloc_shadow_vmcs.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c76ca0e501cf..fc2870dddfe9 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5398,9 +5398,10 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		 * To use VMXON (and later other VMX instructions), a guest
 		 * must first be able to turn on cr4.VMXE (see handle_vmon()).
 		 * So basically the check on whether to allow nested VMX
-		 * is here.
+		 * is here.  We operate under the default treatment of SMM,
+		 * so VMX cannot be enabled under SMM.
 		 */
-		if (!nested_vmx_allowed(vcpu))
+		if (!nested_vmx_allowed(vcpu) || is_smm(vcpu))
 			return 1;
 	}
 
@@ -13977,6 +13978,14 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	    ~(KVM_STATE_NESTED_SMM_GUEST_MODE | KVM_STATE_NESTED_SMM_VMXON))
 		return -EINVAL;
 
+	/*
+	 * SMM temporarily disables VMX, so we cannot be in guest mode,
+	 * nor can VMLAUNCH/VMRESUME be pending.  Outside SMM, SMM flags
+	 * must be zero.
+	 */
+	if (is_smm(vcpu) ? kvm_state->flags : kvm_state->vmx.smm.flags)
+		return -EINVAL;
+
 	if ((kvm_state->vmx.smm.flags & KVM_STATE_NESTED_SMM_GUEST_MODE) &&
 	    !(kvm_state->vmx.smm.flags & KVM_STATE_NESTED_SMM_VMXON))
 		return -EINVAL;
-- 
1.8.3.1