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KVM: nVMX: fix nested_vmx_check_vmptr failure paths under debugging
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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: 6affcbe ("KVM: x86: Add kvm_skip_emulated_instruction and use it.")
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Radim Krčmář authored and Paolo Bonzini committed May 30, 2017
1 parent 52b5419 commit cbf7127
Showing 1 changed file with 57 additions and 83 deletions.
140 changes: 57 additions & 83 deletions arch/x86/kvm/vmx.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}

Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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;
Expand Down

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