[PATCH v2 2/2] kvm: vmx: segment limit check: use access length

[PATCH v2 2/2] kvm: vmx: segment limit check: use access length

[Eugene Korenevsky]

There is an imperfection in get_vmx_mem_address(): access length is ignored
when checking the limit. To fix this, pass access length as a function argument.
The access length is obvious since it is used by callers after
get_vmx_mem_address() call.

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>
---
Changes in v2: fixed logical bug (`len` argument was not used inside
get_vmx_mem_address() function); fixed the subject

 arch/x86/kvm/vmx/nested.c | 28 ++++++++++++++++------------
 arch/x86/kvm/vmx/nested.h |  2 +-
 arch/x86/kvm/vmx/vmx.c    |  3 ++-
 3 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index fef3d7031715..918629c79c4a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4008,7 +4008,7 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
  * #UD or #GP.
  */
 int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
-			u32 vmx_instruction_info, bool wr, gva_t *ret)
+			u32 vmx_instruction_info, bool wr, int len, gva_t *ret)
 {
 	gva_t off;
 	bool exn;
@@ -4115,7 +4115,7 @@ int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
 		 */
 		if (!(s.base == 0 && s.limit == 0xffffffff &&
 		     ((s.type & 8) || !(s.type & 4))))
-			exn = exn || (off > s.limit + 1 - sizeof(u64));
+			exn = exn || (off > s.limit + 1 - len);
 	}
 	if (exn) {
 		kvm_queue_exception_e(vcpu,
@@ -4134,7 +4134,8 @@ static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer)
 	struct x86_exception e;
 
 	if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
-			vmcs_read32(VMX_INSTRUCTION_INFO), false, &gva))
+				vmcs_read32(VMX_INSTRUCTION_INFO), false,
+				sizeof(*vmpointer), &gva))
 		return 1;
 
 	if (kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e)) {
@@ -4386,6 +4387,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
 	u64 field_value;
 	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;
 
@@ -4423,12 +4425,12 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
 		kvm_register_writel(vcpu, (((vmx_instruction_info) >> 3) & 0xf),
 			field_value);
 	} else {
+		len = is_64_bit_mode(vcpu) ? 8 : 4;
 		if (get_vmx_mem_address(vcpu, exit_qualification,
-				vmx_instruction_info, true, &gva))
+				vmx_instruction_info, true, len, &gva))
 			return 1;
 		/* _system ok, nested_vmx_check_permission has verified cpl=0 */
-		kvm_write_guest_virt_system(vcpu, gva, &field_value,
-					    (is_long_mode(vcpu) ? 8 : 4), NULL);
+		kvm_write_guest_virt_system(vcpu, gva, &field_value, len, NULL);
 	}
 
 	return nested_vmx_succeed(vcpu);
@@ -4438,6 +4440,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
 static int handle_vmwrite(struct kvm_vcpu *vcpu)
 {
 	unsigned long field;
+	int len;
 	gva_t gva;
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
@@ -4463,11 +4466,11 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
 		field_value = kvm_register_readl(vcpu,
 			(((vmx_instruction_info) >> 3) & 0xf));
 	else {
+		len = is_64_bit_mode(vcpu) ? 8 : 4;
 		if (get_vmx_mem_address(vcpu, exit_qualification,
-				vmx_instruction_info, false, &gva))
+				vmx_instruction_info, false, len, &gva))
 			return 1;
-		if (kvm_read_guest_virt(vcpu, gva, &field_value,
-					(is_64_bit_mode(vcpu) ? 8 : 4), &e)) {
+		if (kvm_read_guest_virt(vcpu, gva, &field_value, len, &e)) {
 			kvm_inject_page_fault(vcpu, &e);
 			return 1;
 		}
@@ -4615,7 +4618,8 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
 	if (unlikely(to_vmx(vcpu)->nested.hv_evmcs))
 		return 1;
 
-	if (get_vmx_mem_address(vcpu, exit_qual, instr_info, true, &gva))
+	if (get_vmx_mem_address(vcpu, exit_qual, instr_info,
+				true, sizeof(gpa_t), &gva))
 		return 1;
 	/* *_system ok, nested_vmx_check_permission has verified cpl=0 */
 	if (kvm_write_guest_virt_system(vcpu, gva, (void *)&current_vmptr,
@@ -4661,7 +4665,7 @@ static int handle_invept(struct kvm_vcpu *vcpu)
 	 * operand is read even if it isn't needed (e.g., for type==global)
 	 */
 	if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
-			vmx_instruction_info, false, &gva))
+			vmx_instruction_info, false, sizeof(operand), &gva))
 		return 1;
 	if (kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e)) {
 		kvm_inject_page_fault(vcpu, &e);
@@ -4723,7 +4727,7 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
 	 * operand is read even if it isn't needed (e.g., for type==global)
 	 */
 	if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
-			vmx_instruction_info, false, &gva))
+			vmx_instruction_info, false, sizeof(operand), &gva))
 		return 1;
 	if (kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e)) {
 		kvm_inject_page_fault(vcpu, &e);
diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
index e847ff1019a2..29d205bb4e4f 100644
--- a/arch/x86/kvm/vmx/nested.h
+++ b/arch/x86/kvm/vmx/nested.h
@@ -21,7 +21,7 @@ void nested_sync_from_vmcs12(struct kvm_vcpu *vcpu);
 int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data);
 int vmx_get_vmx_msr(struct nested_vmx_msrs *msrs, u32 msr_index, u64 *pdata);
 int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
-			u32 vmx_instruction_info, bool wr, gva_t *ret);
+			u32 vmx_instruction_info, bool wr, int len, gva_t *ret);
 
 static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)
 {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1ac167614032..6ecf9e4de2f9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5342,7 +5342,8 @@ static int handle_invpcid(struct kvm_vcpu *vcpu)
 	 * is read even if it isn't needed (e.g., for type==all)
 	 */
 	if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
-				vmx_instruction_info, false, &gva))
+				vmx_instruction_info, false,
+				sizeof(operand), &gva))
 		return 1;
 
 	if (kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e)) {
-- 
2.21.0