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Subject[PATCH v2] KVM: nVMX: fix nested_vmx_check_vmptr failure paths under debugging
Date
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@oracle.com>
Fixes: 6affcbedcac7 ("KVM: x86: Add kvm_skip_emulated_instruction and use it.")
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
Second try -- moves a lot of code around to make it less ugly and keep
the same behavior as v1, hopefully.

arch/x86/kvm/vmx.c | 140 ++++++++++++++++++++++-------------------------------
1 file changed, 57 insertions(+), 83 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9ff1b04502c9..dd274db9bf77 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6914,97 +6914,21 @@ static int get_vmx_mem_address(struct kvm_vcpu *vcpu,
return 0;
}

-/*
- * This function performs the various checks including
- * - if it's 4KB aligned
- * - No bits beyond the physical address width are set
- * - Returns 0 on success or else 1
- * (Intel SDM Section 30.3)
- */
-static int nested_vmx_check_vmptr(struct kvm_vcpu *vcpu, int exit_reason,
- gpa_t *vmpointer)
+static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer)
{
gva_t gva;
- gpa_t vmptr;
struct x86_exception e;
- struct page *page;
- struct vcpu_vmx *vmx = to_vmx(vcpu);
- int maxphyaddr = cpuid_maxphyaddr(vcpu);

if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
vmcs_read32(VMX_INSTRUCTION_INFO), false, &gva))
return 1;

- if (kvm_read_guest_virt(&vcpu->arch.emulate_ctxt, gva, &vmptr,
- sizeof(vmptr), &e)) {
+ if (kvm_read_guest_virt(&vcpu->arch.emulate_ctxt, gva, vmpointer,
+ sizeof(*vmpointer), &e)) {
kvm_inject_page_fault(vcpu, &e);
return 1;
}

- switch (exit_reason) {
- case EXIT_REASON_VMON:
- /*
- * SDM 3: 24.11.5
- * The first 4 bytes of VMXON region contain the supported
- * VMCS revision identifier
- *
- * Note - IA32_VMX_BASIC[48] will never be 1
- * for the nested case;
- * which replaces physical address width with 32
- *
- */
- if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
- nested_vmx_failInvalid(vcpu);
- return kvm_skip_emulated_instruction(vcpu);
- }
-
- page = nested_get_page(vcpu, vmptr);
- if (page == NULL) {
- nested_vmx_failInvalid(vcpu);
- return kvm_skip_emulated_instruction(vcpu);
- }
- if (*(u32 *)kmap(page) != VMCS12_REVISION) {
- kunmap(page);
- nested_release_page_clean(page);
- nested_vmx_failInvalid(vcpu);
- return kvm_skip_emulated_instruction(vcpu);
- }
- kunmap(page);
- nested_release_page_clean(page);
- vmx->nested.vmxon_ptr = vmptr;
- break;
- case EXIT_REASON_VMCLEAR:
- if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
- nested_vmx_failValid(vcpu,
- VMXERR_VMCLEAR_INVALID_ADDRESS);
- return kvm_skip_emulated_instruction(vcpu);
- }
-
- if (vmptr == vmx->nested.vmxon_ptr) {
- nested_vmx_failValid(vcpu,
- VMXERR_VMCLEAR_VMXON_POINTER);
- return kvm_skip_emulated_instruction(vcpu);
- }
- 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);
- }
-
- if (vmptr == vmx->nested.vmxon_ptr) {
- nested_vmx_failValid(vcpu,
- VMXERR_VMPTRLD_VMXON_POINTER);
- return kvm_skip_emulated_instruction(vcpu);
- }
- break;
- default:
- return 1; /* shouldn't happen */
- }
-
- if (vmpointer)
- *vmpointer = vmptr;
return 0;
}

@@ -7066,6 +6990,8 @@ static int enter_vmx_operation(struct kvm_vcpu *vcpu)
static int handle_vmon(struct kvm_vcpu *vcpu)
{
int ret;
+ gpa_t vmptr;
+ struct page *page;
struct vcpu_vmx *vmx = to_vmx(vcpu);
const u64 VMXON_NEEDED_FEATURES = FEATURE_CONTROL_LOCKED
| FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
@@ -7095,9 +7021,37 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
return 1;
}

- if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMON, NULL))
+ if (nested_vmx_get_vmptr(vcpu, &vmptr))
return 1;
-
+
+ /*
+ * SDM 3: 24.11.5
+ * The first 4 bytes of VMXON region contain the supported
+ * VMCS revision identifier
+ *
+ * Note - IA32_VMX_BASIC[48] will never be 1 for the nested case;
+ * which replaces physical address width with 32
+ */
+ if (!PAGE_ALIGNED(vmptr) || (vmptr >> cpuid_maxphyaddr(vcpu))) {
+ nested_vmx_failInvalid(vcpu);
+ return kvm_skip_emulated_instruction(vcpu);
+ }
+
+ page = nested_get_page(vcpu, vmptr);
+ if (page == NULL) {
+ nested_vmx_failInvalid(vcpu);
+ return kvm_skip_emulated_instruction(vcpu);
+ }
+ if (*(u32 *)kmap(page) != VMCS12_REVISION) {
+ kunmap(page);
+ nested_release_page_clean(page);
+ nested_vmx_failInvalid(vcpu);
+ return kvm_skip_emulated_instruction(vcpu);
+ }
+ kunmap(page);
+ nested_release_page_clean(page);
+
+ vmx->nested.vmxon_ptr = vmptr;
ret = enter_vmx_operation(vcpu);
if (ret)
return ret;
@@ -7213,9 +7167,19 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
if (!nested_vmx_check_permission(vcpu))
return 1;

- if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMCLEAR, &vmptr))
+ if (nested_vmx_get_vmptr(vcpu, &vmptr))
return 1;

+ if (!PAGE_ALIGNED(vmptr) || (vmptr >> cpuid_maxphyaddr(vcpu))) {
+ nested_vmx_failValid(vcpu, VMXERR_VMCLEAR_INVALID_ADDRESS);
+ return kvm_skip_emulated_instruction(vcpu);
+ }
+
+ if (vmptr == vmx->nested.vmxon_ptr) {
+ nested_vmx_failValid(vcpu, VMXERR_VMCLEAR_VMXON_POINTER);
+ return kvm_skip_emulated_instruction(vcpu);
+ }
+
if (vmptr == vmx->nested.current_vmptr)
nested_release_vmcs12(vmx);

@@ -7545,9 +7509,19 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
if (!nested_vmx_check_permission(vcpu))
return 1;

- if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMPTRLD, &vmptr))
+ if (nested_vmx_get_vmptr(vcpu, &vmptr))
return 1;

+ if (!PAGE_ALIGNED(vmptr) || (vmptr >> cpuid_maxphyaddr(vcpu))) {
+ nested_vmx_failValid(vcpu, VMXERR_VMPTRLD_INVALID_ADDRESS);
+ return kvm_skip_emulated_instruction(vcpu);
+ }
+
+ if (vmptr == vmx->nested.vmxon_ptr) {
+ nested_vmx_failValid(vcpu, VMXERR_VMPTRLD_VMXON_POINTER);
+ return kvm_skip_emulated_instruction(vcpu);
+ }
+
if (vmx->nested.current_vmptr != vmptr) {
struct vmcs12 *new_vmcs12;
struct page *page;
--
2.13.0
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