[PATCH 1/4] KVM: nVMX: fix nested_vmx_check_vmptr failure paths under debugging

[Radim Krčmář <rkrcmar@xxxxxxxxxx>]

kvm_skip_emulated_instruction() will return 0 if userspace is
single-stepping the guest.

kvm_skip_emulated_instruction() uses return status convention of exit
handler: 0 means "exit to userspace" and 1 means "continue vm entries".
The problem is that nested_vmx_check_vmptr() return status means
something else: 0 is ok, 1 is error.

This means we would continue executing after a failure.  Static checker
noticed it because vmptr was not initialized.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Fixes: 6affcbedcac7 ("KVM: x86: Add kvm_skip_emulated_instruction and use it.")
Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
---
  TODO: add enum for exit handler return states.
---
 arch/x86/kvm/vmx.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9ff1b04502c9..35e058ddd97a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6955,19 +6955,19 @@ static int nested_vmx_check_vmptr(struct kvm_vcpu *vcpu, int exit_reason,
 		 */
 		if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
 			nested_vmx_failInvalid(vcpu);
-			return kvm_skip_emulated_instruction(vcpu);
+			return 2;
 		}
 
 		page = nested_get_page(vcpu, vmptr);
 		if (page == NULL) {
 			nested_vmx_failInvalid(vcpu);
-			return kvm_skip_emulated_instruction(vcpu);
+			return 2;
 		}
 		if (*(u32 *)kmap(page) != VMCS12_REVISION) {
 			kunmap(page);
 			nested_release_page_clean(page);
 			nested_vmx_failInvalid(vcpu);
-			return kvm_skip_emulated_instruction(vcpu);
+			return 2;
 		}
 		kunmap(page);
 		nested_release_page_clean(page);
@@ -6977,26 +6977,26 @@ static int nested_vmx_check_vmptr(struct kvm_vcpu *vcpu, int exit_reason,
 		if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMCLEAR_INVALID_ADDRESS);
-			return kvm_skip_emulated_instruction(vcpu);
+			return 2;
 		}
 
 		if (vmptr == vmx->nested.vmxon_ptr) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMCLEAR_VMXON_POINTER);
-			return kvm_skip_emulated_instruction(vcpu);
+			return 2;
 		}
 		break;
 	case EXIT_REASON_VMPTRLD:
 		if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMPTRLD_INVALID_ADDRESS);
-			return kvm_skip_emulated_instruction(vcpu);
+			return 2;
 		}
 
 		if (vmptr == vmx->nested.vmxon_ptr) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMPTRLD_VMXON_POINTER);
-			return kvm_skip_emulated_instruction(vcpu);
+			return 2;
 		}
 		break;
 	default:
@@ -7095,8 +7095,9 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
 		return 1;
 	}
 
-	if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMON, NULL))
-		return 1;
+	ret = nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMON, NULL);
+	if (ret)
+		return ret == 1 ? 1 : kvm_skip_emulated_instruction(vcpu);
  
 	ret = enter_vmx_operation(vcpu);
 	if (ret)
@@ -7209,12 +7210,14 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 zero = 0;
 	gpa_t vmptr;
+	int ret;
 
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMCLEAR, &vmptr))
-		return 1;
+	ret = nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMCLEAR, &vmptr);
+	if (ret)
+		return ret == 1 ? 1 : kvm_skip_emulated_instruction(vcpu);
 
 	if (vmptr == vmx->nested.current_vmptr)
 		nested_release_vmcs12(vmx);
@@ -7541,12 +7544,14 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	gpa_t vmptr;
+	int ret;
 
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMPTRLD, &vmptr))
-		return 1;
+	ret = nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMPTRLD, &vmptr);
+	if (ret)
+		return ret == 1 ? 1 : kvm_skip_emulated_instruction(vcpu);
 
 	if (vmx->nested.current_vmptr != vmptr) {
 		struct vmcs12 *new_vmcs12;
-- 
2.13.0