[PATCH v3 3/7] KVM: SVM: Move RAX legality check to SVM insn interception handlers

[Yosry Ahmed]

When #GP is intercepted by KVM, the #GP interception handler checks
whether the GPA in RAX is legal and reinjects the #GP accordingly.
Otherwise, it calls into the appropriate interception handler for
VMRUN/VMLOAD/VMSAVE. The intercept handlers do not check RAX.

However, according to the APM, the interception takes precedence
over #GP due to an invalid operand:

  Generally, instruction intercepts are checked after simple exceptions
  (such as #GP—when CPL is incorrect—or #UD) have been checked, but
  before exceptions related to memory accesses (such as page faults) and
  exceptions based on specific operand values.

Move the check into the interception handlers for VMRUN/VMLOAD/VMSAVE as
the CPU does not check RAX before the interception.

Opportunisitically make the non-SVM insn path in gp_interception() do an
early return to reduce intendation.

Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
---
 arch/x86/kvm/svm/nested.c |  5 +++++
 arch/x86/kvm/svm/svm.c    | 34 +++++++++++++++++-----------------
 2 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 5ff01d2ac85e4..016bf88ec2def 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1115,6 +1115,11 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 
 	vmcb12_gpa = svm->vmcb->save.rax;
 
+	if (!page_address_valid(vcpu, vmcb12_gpa)) {
+		kvm_inject_gp(vcpu, 0);
+		return 1;
+	}
+
 	ret = nested_svm_copy_vmcb12_to_cache(vcpu, vmcb12_gpa);
 	if (ret) {
 		if (ret == -EFAULT) {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 796a6887305d6..f019a3f7705ae 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2183,6 +2183,7 @@ static int intr_interception(struct kvm_vcpu *vcpu)
 static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+	u64 vmcb12_gpa = svm->vmcb->save.rax;
 	struct vmcb *vmcb12;
 	struct kvm_host_map map;
 	int ret;
@@ -2190,7 +2191,12 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
 	if (nested_svm_check_permissions(vcpu))
 		return 1;
 
-	ret = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
+	if (!page_address_valid(vcpu, vmcb12_gpa)) {
+		kvm_inject_gp(vcpu, 0);
+		return 1;
+	}
+
+	ret = kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map);
 	if (ret) {
 		if (ret == -EINVAL)
 			kvm_inject_gp(vcpu, 0);
@@ -2306,24 +2312,18 @@ static int gp_interception(struct kvm_vcpu *vcpu)
 		goto reinject;
 
 	opcode = svm_instr_opcode(vcpu);
+	if (opcode != NONE_SVM_INSTR)
+		return emulate_svm_instr(vcpu, opcode);
 
-	if (opcode == NONE_SVM_INSTR) {
-		if (!enable_vmware_backdoor)
-			goto reinject;
-
-		/*
-		 * VMware backdoor emulation on #GP interception only handles
-		 * IN{S}, OUT{S}, and RDPMC.
-		 */
-		if (!is_guest_mode(vcpu))
-			return kvm_emulate_instruction(vcpu,
-				EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE);
-	} else {
-		if (!page_address_valid(vcpu, svm->vmcb->save.rax))
-			goto reinject;
+	if (!enable_vmware_backdoor)
+		goto reinject;
 
-		return emulate_svm_instr(vcpu, opcode);
-	}
+	/*
+	 * VMware backdoor emulation on #GP interception only handles
+	 * IN{S}, OUT{S}, and RDPMC.
+	 */
+	if (!is_guest_mode(vcpu))
+		return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE);
 
 reinject:
 	kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
-- 
2.53.0.851.ga537e3e6e9-goog