Re: [PATCH] kvm: nVMX: VMWRITE checks VMCS-link pointer before VMCS field

[Paolo Bonzini <pbonzini@redhat.com>]

On 04/12/19 22:40, Jim Mattson wrote:
> 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.
> 
> Fixes: 6d894f498f5d1 ("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>
> ---
>  arch/x86/kvm/vmx/nested.c | 38 +++++++++++++++++++-------------------
>  1 file changed, 19 insertions(+), 19 deletions(-)

As Vitaly pointed out, the test must be split in two, like this:

---------------- 8< -----------------------
From 3b9d87060e800ffae2bd19da94ede05018066c87 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu, 5 Dec 2019 12:39:07 +0100
Subject: [PATCH] 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.

While cleaning up handle_vmwrite, make the code of handle_vmread look
the same, too.

Fixes: 6d894f498f5d1 ("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>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4aea7d304beb..c080a879b95d 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4767,14 +4767,13 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
 	if (to_vmx(vcpu)->nested.current_vmptr == -1ull)
 		return nested_vmx_failInvalid(vcpu);

-	if (!is_guest_mode(vcpu))
-		vmcs12 = get_vmcs12(vcpu);
-	else {
+	vmcs12 = get_vmcs12(vcpu);
+	if (is_guest_mode(vcpu)) {
 		/*
 		 * When vmcs->vmcs_link_pointer is -1ull, any VMREAD
 		 * to shadowed-field sets the ALU flags for VMfailInvalid.
 		 */
-		if (get_vmcs12(vcpu)->vmcs_link_pointer == -1ull)
+		if (vmcs12->vmcs_link_pointer == -1ull)
 			return nested_vmx_failInvalid(vcpu);
 		vmcs12 = get_shadow_vmcs12(vcpu);
 	}
@@ -4878,8 +4877,19 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
 		}
 	}

+	vmcs12 = get_vmcs12(vcpu);
+	if (is_guest_mode(vcpu)) {
+		/*
+		 * When vmcs->vmcs_link_pointer is -1ull, any VMWRITE
+		 * to shadowed-field sets the ALU flags for VMfailInvalid.
+		 */
+		if (vmcs12->vmcs_link_pointer == -1ull)
+			return nested_vmx_failInvalid(vcpu);
+		vmcs12 = get_shadow_vmcs12(vcpu);
+	}

 	field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
+
 	/*
 	 * If the vCPU supports "VMWRITE to any supported field in the
 	 * VMCS," then the "read-only" fields are actually read/write.
@@ -4889,24 +4899,12 @@ 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))
-			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);
-	}
+	/*
+	 * 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_guest_mode(vcpu) && !is_shadow_field_rw(field))
+		copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);

 	offset = vmcs_field_to_offset(field);
 	if (offset < 0)


... and also, do you have a matching kvm-unit-tests patch?

Thanks,

Paolo