kvm: nVMX: VMWRITE checks VMCS-link pointer before VMCS field

According to the SDM, a VMWRITE in VMX non-root operation with an
invalid VMCS-link pointer results in VMfailInvalid before the validity
of the VMCS field in the secondary source operand is checked.

For consistency, modify both handle_vmwrite and handle_vmread, even
though there was no problem with the latter.

Fixes: 6d894f49 ("KVM: nVMX: vmread/vmwrite: Use shadow vmcs12 if running L2")
Signed-off-by: Jim Mattson <jmattson@google.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Peter Shier <pshier@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Reviewed-by: Jon Cargille <jcargill@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -4753,31 +4753,27 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
 {
 	unsigned long field;
 	u64 field_value;
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 	u32 vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
 	int len;
 	gva_t gva = 0;
-	struct vmcs12 *vmcs12;
+	struct vmcs12 *vmcs12 = is_guest_mode(vcpu) ? get_shadow_vmcs12(vcpu)
+						    : get_vmcs12(vcpu);
 	struct x86_exception e;
 	short offset;
 
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (to_vmx(vcpu)->nested.current_vmptr == -1ull)
-		return nested_vmx_failInvalid(vcpu);
-
-	if (!is_guest_mode(vcpu))
-		vmcs12 = get_vmcs12(vcpu);
-	else {
 	/*
-		 * When vmcs->vmcs_link_pointer is -1ull, any VMREAD
-		 * to shadowed-field sets the ALU flags for VMfailInvalid.
+	 * In VMX non-root operation, when the VMCS-link pointer is -1ull,
+	 * any VMREAD sets the ALU flags for VMfailInvalid.
 	 */
-		if (get_vmcs12(vcpu)->vmcs_link_pointer == -1ull)
+	if (vmx->nested.current_vmptr == -1ull ||
+	    (is_guest_mode(vcpu) &&
+	     get_vmcs12(vcpu)->vmcs_link_pointer == -1ull))
 		return nested_vmx_failInvalid(vcpu);
-		vmcs12 = get_shadow_vmcs12(vcpu);
-	}
 
 	/* Decode instruction info and find the field to read */
 	field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
@@ -4855,13 +4851,20 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
 	 */
 	u64 field_value = 0;
 	struct x86_exception e;
-	struct vmcs12 *vmcs12;
+	struct vmcs12 *vmcs12 = is_guest_mode(vcpu) ? get_shadow_vmcs12(vcpu)
+						    : get_vmcs12(vcpu);
 	short offset;
 
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (vmx->nested.current_vmptr == -1ull)
+	/*
+	 * In VMX non-root operation, when the VMCS-link pointer is -1ull,
+	 * any VMWRITE sets the ALU flags for VMfailInvalid.
+	 */
+	if (vmx->nested.current_vmptr == -1ull ||
+	    (is_guest_mode(vcpu) &&
+	     get_vmcs12(vcpu)->vmcs_link_pointer == -1ull))
 		return nested_vmx_failInvalid(vcpu);
 
 	if (vmx_instruction_info & (1u << 10))
@@ -4889,24 +4892,12 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
 		return nested_vmx_failValid(vcpu,
 			VMXERR_VMWRITE_READ_ONLY_VMCS_COMPONENT);
 
-	if (!is_guest_mode(vcpu)) {
-		vmcs12 = get_vmcs12(vcpu);
-
 	/*
 	 * Ensure vmcs12 is up-to-date before any VMWRITE that dirties
 	 * vmcs12, else we may crush a field or consume a stale value.
 	 */
-		if (!is_shadow_field_rw(field))
+	if (!is_guest_mode(vcpu) && !is_shadow_field_rw(field))
 		copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
-	} else {
-		/*
-		 * When vmcs->vmcs_link_pointer is -1ull, any VMWRITE
-		 * to shadowed-field sets the ALU flags for VMfailInvalid.
-		 */
-		if (get_vmcs12(vcpu)->vmcs_link_pointer == -1ull)
-			return nested_vmx_failInvalid(vcpu);
-		vmcs12 = get_shadow_vmcs12(vcpu);
-	}
 
 	offset = vmcs_field_to_offset(field);
 	if (offset < 0)