KVM: VMX: check validity of VMCS controls when returning from SMM

The VMCS12 is not available while in SMM.  However, it can be overwritten
if userspace manages to trigger copy_enlightened_to_vmcs12() - for example
via KVM_GET_NESTED_STATE.

Because of this, the VMCS12 has to be checked for validity before it is
used to generate the VMCS02.  Move the check code out of vmx_set_nested_state()
(the other "not a VMLAUNCH/VMRESUME" path that emulates a nested vmentry)
and reuse it in vmx_leave_smm().

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: bonzini

arch/x86/kvm/vmx/nested.c

@@ -6856,13 +6856,34 @@ void vmx_leave_nested(struct kvm_vcpu *vcpu)
 	free_nested(vcpu);
 }
 
+int nested_vmx_check_restored_vmcs12(struct kvm_vcpu *vcpu)
+{
+	enum vm_entry_failure_code ignored;
+	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+
+	if (nested_cpu_has_shadow_vmcs(vmcs12) &&
+	    vmcs12->vmcs_link_pointer != INVALID_GPA) {
+		struct vmcs12 *shadow_vmcs12 = get_shadow_vmcs12(vcpu);
+
+		if (shadow_vmcs12->hdr.revision_id != VMCS12_REVISION ||
+		    !shadow_vmcs12->hdr.shadow_vmcs)
+			return -EINVAL;
+	}
+
+	if (nested_vmx_check_controls(vcpu, vmcs12) ||
+	    nested_vmx_check_host_state(vcpu, vmcs12) ||
+	    nested_vmx_check_guest_state(vcpu, vmcs12, &ignored))
+		return -EINVAL;
+
+	return 0;
+}
+
 static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 				struct kvm_nested_state __user *user_kvm_nested_state,
 				struct kvm_nested_state *kvm_state)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct vmcs12 *vmcs12;
-	enum vm_entry_failure_code ignored;
 	struct kvm_vmx_nested_state_data __user *user_vmx_nested_state =
 		&user_kvm_nested_state->data.vmx[0];
 	int ret;
@@ -6993,25 +7014,20 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	vmx->nested.mtf_pending =
 		!!(kvm_state->flags & KVM_STATE_NESTED_MTF_PENDING);
 
-	ret = -EINVAL;
 	if (nested_cpu_has_shadow_vmcs(vmcs12) &&
 	    vmcs12->vmcs_link_pointer != INVALID_GPA) {
 		struct vmcs12 *shadow_vmcs12 = get_shadow_vmcs12(vcpu);
 
+		ret = -EINVAL;
 		if (kvm_state->size <
 		    sizeof(*kvm_state) +
 		    sizeof(user_vmx_nested_state->vmcs12) + sizeof(*shadow_vmcs12))
 			goto error_guest_mode;
 
+		ret = -EFAULT;
 		if (copy_from_user(shadow_vmcs12,
 				   user_vmx_nested_state->shadow_vmcs12,
-				   sizeof(*shadow_vmcs12))) {
-			ret = -EFAULT;
-			goto error_guest_mode;
-		}
-
-		if (shadow_vmcs12->hdr.revision_id != VMCS12_REVISION ||
-		    !shadow_vmcs12->hdr.shadow_vmcs)
+				   sizeof(*shadow_vmcs12)))
 			goto error_guest_mode;
 	}
 
@@ -7022,9 +7038,8 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 			kvm_state->hdr.vmx.preemption_timer_deadline;
 	}
 
-	if (nested_vmx_check_controls(vcpu, vmcs12) ||
-	    nested_vmx_check_host_state(vcpu, vmcs12) ||
-	    nested_vmx_check_guest_state(vcpu, vmcs12, &ignored))
+	ret = nested_vmx_check_restored_vmcs12(vcpu);
+	if (ret < 0)
 		goto error_guest_mode;
 
 	vmx->nested.dirty_vmcs12 = true;

arch/x86/kvm/vmx/nested.h

@@ -22,6 +22,7 @@ void nested_vmx_setup_ctls_msrs(struct vmcs_config *vmcs_conf, u32 ept_caps);
 void nested_vmx_hardware_unsetup(void);
 __init int nested_vmx_hardware_setup(int (*exit_handlers[])(struct kvm_vcpu *));
 void nested_vmx_set_vmcs_shadowing_bitmap(void);
+int nested_vmx_check_restored_vmcs12(struct kvm_vcpu *vcpu);
 void nested_vmx_free_vcpu(struct kvm_vcpu *vcpu);
 enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 						     bool from_vmentry);

arch/x86/kvm/vmx/vmx.c

@@ -8528,6 +8528,10 @@ int vmx_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram)
 	}
 
 	if (vmx->nested.smm.guest_mode) {
+		/* Triple fault if the state is invalid.  */
+		if (nested_vmx_check_restored_vmcs12(vcpu) < 0)
+			return 1;
+
 		ret = nested_vmx_enter_non_root_mode(vcpu, false);
 		if (ret)
 			return ret;