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KVM: VMX: Properly handle kvm_read/write_guest_virt*() result 

Syzbot reports the following issue:

WARNING: CPU: 0 PID: 6819 at arch/x86/kvm/x86.c:618
 kvm_inject_emulated_page_fault+0x210/0x290 arch/x86/kvm/x86.c:618
...
Call Trace:
...
RIP: 0010:kvm_inject_emulated_page_fault+0x210/0x290 arch/x86/kvm/x86.c:618
...
 nested_vmx_get_vmptr+0x1f9/0x2a0 arch/x86/kvm/vmx/nested.c:4638
 handle_vmon arch/x86/kvm/vmx/nested.c:4767 [inline]
 handle_vmon+0x168/0x3a0 arch/x86/kvm/vmx/nested.c:4728
 vmx_handle_exit+0x29c/0x1260 arch/x86/kvm/vmx/vmx.c:6067

'exception' we're trying to inject with kvm_inject_emulated_page_fault()
comes from:

  nested_vmx_get_vmptr()
   kvm_read_guest_virt()
     kvm_read_guest_virt_helper()
       vcpu->arch.walk_mmu->gva_to_gpa()

but it is only set when GVA to GPA conversion fails. In case it doesn't but
we still fail kvm_vcpu_read_guest_page(), X86EMUL_IO_NEEDED is returned and
nested_vmx_get_vmptr() calls kvm_inject_emulated_page_fault() with zeroed
'exception'. This happen when the argument is MMIO.

Paolo also noticed that nested_vmx_get_vmptr() is not the only place in
KVM code where kvm_read/write_guest_virt*() return result is mishandled.
VMX instructions along with INVPCID have the same issue. This was already
noticed before, e.g. see commit 541ab2aeb2 ("KVM: x86: work around
leak of uninitialized stack contents") but was never fully fixed.

KVM could've handled the request correctly by going to userspace and
performing I/O but there doesn't seem to be a good need for such requests
in the first place.

Introduce vmx_handle_memory_failure() as an interim solution.

Note, nested_vmx_get_vmptr() now has three possible outcomes: OK, PF,
KVM_EXIT_INTERNAL_ERROR and callers need to know if userspace exit is
needed (for KVM_EXIT_INTERNAL_ERROR) in case of failure. We don't seem
to have a good enum describing this tristate, just add "int *ret" to
nested_vmx_get_vmptr() interface to pass the information.

Reported-by: syzbot+2a7156e11dc199bdbd8a@syzkaller.appspotmail.com
Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200605115906.532682-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2020-06-05 13:59:05 +02:00 committed by Paolo Bonzini
parent 34d2618d33
commit 7a35e515a7
3 changed files with 74 additions and 40 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

78
arch/x86/kvm/vmx/nested.c
View File

@ -4624,19 +4624,24 @@ void nested_vmx_pmu_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
}
}
static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer)
static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer,
int *ret)
{
gva_t gva;
struct x86_exception e;
int r;
if (get_vmx_mem_address(vcpu, vmx_get_exit_qual(vcpu),
vmcs_read32(VMX_INSTRUCTION_INFO), false,
sizeof(*vmpointer), &gva))
return 1;
sizeof(*vmpointer), &gva)) {
*ret = 1;
return -EINVAL;
}
if (kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e)) {
kvm_inject_emulated_page_fault(vcpu, &e);
return 1;
r = kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e);
if (r != X86EMUL_CONTINUE) {
*ret = vmx_handle_memory_failure(vcpu, r, &e);
return -EINVAL;
}
return 0;
@ -4764,8 +4769,8 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
return 1;
}
if (nested_vmx_get_vmptr(vcpu, &vmptr))
return 1;
if (nested_vmx_get_vmptr(vcpu, &vmptr, &ret))
return ret;
/*
* SDM 3: 24.11.5
@ -4838,12 +4843,13 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
u32 zero = 0;
gpa_t vmptr;
u64 evmcs_gpa;
int r;
if (!nested_vmx_check_permission(vcpu))
return 1;
if (nested_vmx_get_vmptr(vcpu, &vmptr))
return 1;
if (nested_vmx_get_vmptr(vcpu, &vmptr, &r))
return r;
if (!page_address_valid(vcpu, vmptr))
return nested_vmx_failValid(vcpu,
@ -4902,7 +4908,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
u64 value;
gva_t gva = 0;
short offset;
int len;
int len, r;
if (!nested_vmx_check_permission(vcpu))
return 1;
@ -4943,10 +4949,9 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
instr_info, true, len, &gva))
return 1;
/* _system ok, nested_vmx_check_permission has verified cpl=0 */
if (kvm_write_guest_virt_system(vcpu, gva, &value, len, &e)) {
kvm_inject_emulated_page_fault(vcpu, &e);
return 1;
}
r = kvm_write_guest_virt_system(vcpu, gva, &value, len, &e);
if (r != X86EMUL_CONTINUE)
return vmx_handle_memory_failure(vcpu, r, &e);
}
return nested_vmx_succeed(vcpu);
@ -4987,7 +4992,7 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
unsigned long field;
short offset;
gva_t gva;
int len;
int len, r;
/*
* The value to write might be 32 or 64 bits, depending on L1's long
@ -5017,10 +5022,9 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
if (get_vmx_mem_address(vcpu, exit_qualification,
instr_info, false, len, &gva))
return 1;
if (kvm_read_guest_virt(vcpu, gva, &value, len, &e)) {
kvm_inject_emulated_page_fault(vcpu, &e);
return 1;
}
r = kvm_read_guest_virt(vcpu, gva, &value, len, &e);
if (r != X86EMUL_CONTINUE)
return vmx_handle_memory_failure(vcpu, r, &e);
}
field = kvm_register_readl(vcpu, (((instr_info) >> 28) & 0xf));
@ -5103,12 +5107,13 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
gpa_t vmptr;
int r;
if (!nested_vmx_check_permission(vcpu))
return 1;
if (nested_vmx_get_vmptr(vcpu, &vmptr))
return 1;
if (nested_vmx_get_vmptr(vcpu, &vmptr, &r))
return r;
if (!page_address_valid(vcpu, vmptr))
return nested_vmx_failValid(vcpu,
@ -5170,6 +5175,7 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
gpa_t current_vmptr = to_vmx(vcpu)->nested.current_vmptr;
struct x86_exception e;
gva_t gva;
int r;
if (!nested_vmx_check_permission(vcpu))
return 1;
@ -5181,11 +5187,11 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
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,
sizeof(gpa_t), &e)) {
kvm_inject_emulated_page_fault(vcpu, &e);
return 1;
}
r = kvm_write_guest_virt_system(vcpu, gva, (void *)&current_vmptr,
sizeof(gpa_t), &e);
if (r != X86EMUL_CONTINUE)
return vmx_handle_memory_failure(vcpu, r, &e);
return nested_vmx_succeed(vcpu);
}
@ -5209,7 +5215,7 @@ static int handle_invept(struct kvm_vcpu *vcpu)
struct {
u64 eptp, gpa;
} operand;
int i;
int i, r;
if (!(vmx->nested.msrs.secondary_ctls_high &
SECONDARY_EXEC_ENABLE_EPT) ||
@ -5236,10 +5242,9 @@ static int handle_invept(struct kvm_vcpu *vcpu)
if (get_vmx_mem_address(vcpu, vmx_get_exit_qual(vcpu),
vmx_instruction_info, false, sizeof(operand), &gva))
return 1;
if (kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e)) {
kvm_inject_emulated_page_fault(vcpu, &e);
return 1;
}
r = kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e);
if (r != X86EMUL_CONTINUE)
return vmx_handle_memory_failure(vcpu, r, &e);
/*
* Nested EPT roots are always held through guest_mmu,
@ -5291,6 +5296,7 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
u64 gla;
} operand;
u16 vpid02;
int r;
if (!(vmx->nested.msrs.secondary_ctls_high &
SECONDARY_EXEC_ENABLE_VPID) ||
@ -5318,10 +5324,10 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
if (get_vmx_mem_address(vcpu, vmx_get_exit_qual(vcpu),
vmx_instruction_info, false, sizeof(operand), &gva))
return 1;
if (kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e)) {
kvm_inject_emulated_page_fault(vcpu, &e);
return 1;
}
r = kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e);
if (r != X86EMUL_CONTINUE)
return vmx_handle_memory_failure(vcpu, r, &e);
if (operand.vpid >> 16)
return nested_vmx_failValid(vcpu,
VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);

34
arch/x86/kvm/vmx/vmx.c
View File

@ -1600,6 +1600,32 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
return 1;
}
/*
* Handles kvm_read/write_guest_virt*() result and either injects #PF or returns
* KVM_EXIT_INTERNAL_ERROR for cases not currently handled by KVM. Return value
* indicates whether exit to userspace is needed.
*/
int vmx_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
struct x86_exception *e)
{
if (r == X86EMUL_PROPAGATE_FAULT) {
kvm_inject_emulated_page_fault(vcpu, e);
return 1;
}
/*
* In case kvm_read/write_guest_virt*() failed with X86EMUL_IO_NEEDED
* while handling a VMX instruction KVM could've handled the request
* correctly by exiting to userspace and performing I/O but there
* doesn't seem to be a real use-case behind such requests, just return
* KVM_EXIT_INTERNAL_ERROR for now.
*/
vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
vcpu->run->internal.ndata = 0;
return 0;
}
/*
* Recognizes a pending MTF VM-exit and records the nested state for later
@ -5486,6 +5512,7 @@ static int handle_invpcid(struct kvm_vcpu *vcpu)
u64 pcid;
u64 gla;
} operand;
int r;
if (!guest_cpuid_has(vcpu, X86_FEATURE_INVPCID)) {
kvm_queue_exception(vcpu, UD_VECTOR);
@ -5508,10 +5535,9 @@ static int handle_invpcid(struct kvm_vcpu *vcpu)
sizeof(operand), &gva))
return 1;
if (kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e)) {
kvm_inject_emulated_page_fault(vcpu, &e);
return 1;
}
r = kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e);
if (r != X86EMUL_CONTINUE)
return vmx_handle_memory_failure(vcpu, r, &e);
if (operand.pcid >> 12 != 0) {
kvm_inject_gp(vcpu, 0);

2
arch/x86/kvm/vmx/vmx.h
View File

@ -355,6 +355,8 @@ struct shared_msr_entry *find_msr_entry(struct vcpu_vmx *vmx, u32 msr);
void pt_update_intercept_for_msr(struct vcpu_vmx *vmx);
void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp);
int vmx_find_msr_index(struct vmx_msrs *m, u32 msr);
int vmx_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
struct x86_exception *e);
#define POSTED_INTR_ON 0
#define POSTED_INTR_SN 1