[PATCH 1/1] kvm: nVMX: Checks "VMCS shadowing" with VMCS link pointer for non-root mode VM{READ,WRITE}

[Yuan Yao <yuan.yao@xxxxxxxxx>]

Add checking to VMCS12's "VMCS shadowing", make sure the checking of
VMCS12's vmcs_link_pointer for non-root mode VM{READ,WRITE} happens
only if VMCS12's "VMCS shadowing" is 1.

SDM says that for non-root mode the VMCS's "VMCS shadowing" must be 1
(and the corresponding bits in VMREAD/VMWRITE bitmap must be 0) when
condition checking of [B] is reached(please refer [A]), which means
checking to VMCS link pointer for non-root mode VM{READ,WRITE} should
happen only when "VMCS shadowing" = 1.

Description from SDM Vol3(April 2022) Chapter 30.3 VMREAD/VMWRITE:

IF (not in VMX operation)
   or (CR0.PE = 0)
   or (RFLAGS.VM = 1)
   or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
      AND (“VMCS shadowing” is 0 OR
           source operand sets bits in range 63:15 OR
           VMREAD bit corresponding to bits 14:0 of source
           operand is 1)  <------[A]
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSIF (in VMX root operation AND current-VMCS pointer is not valid) OR
      (in VMX non-root operation AND VMCS link pointer is not valid)
THEN VMfailInvalid;  <------ [B]
...

Fixes: dd2d6042b7f4 ("kvm: nVMX: VMWRITE checks VMCS-link pointer before VMCS field")
Signed-off-by: Yuan Yao <yuan.yao@xxxxxxxxx>
---
 arch/x86/kvm/vmx/nested.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index ddd4367d4826..30685be54c5d 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5123,6 +5123,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
 		 */
 		if (vmx->nested.current_vmptr == INVALID_GPA ||
 		    (is_guest_mode(vcpu) &&
+		     nested_cpu_has_shadow_vmcs(vcpu) &&
 		     get_vmcs12(vcpu)->vmcs_link_pointer == INVALID_GPA))
 			return nested_vmx_failInvalid(vcpu);
 
@@ -5233,6 +5234,7 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
 	 */
 	if (vmx->nested.current_vmptr == INVALID_GPA ||
 	    (is_guest_mode(vcpu) &&
+	     nested_cpu_has_shadow_vmcs(vcpu) &&
 	     get_vmcs12(vcpu)->vmcs_link_pointer == INVALID_GPA))
 		return nested_vmx_failInvalid(vcpu);
 
-- 
2.27.0