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KVM: x86: Handle triple fault in L2 without killing L1 

Synthesize a nested VM-Exit if L2 triggers an emulated triple fault
instead of exiting to userspace, which likely will kill L1.  Any flow
that does KVM_REQ_TRIPLE_FAULT is suspect, but the most common scenario
for L2 killing L1 is if L0 (KVM) intercepts a contributory exception that
is _not_intercepted by L1.  E.g. if KVM is intercepting #GPs for the
VMware backdoor, a #GP that occurs in L2 while vectoring an injected #DF
will cause KVM to emulate triple fault.

Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210302174515.2812275-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-03-02 09:45:14 -08:00 committed by Paolo Bonzini
parent 6312975417
commit cb6a32c2b8
6 changed files with 50 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/kvm_host.h
View File

@ -1340,6 +1340,7 @@ struct kvm_x86_ops {
struct kvm_x86_nested_ops {
int (*check_events)(struct kvm_vcpu *vcpu);
bool (*hv_timer_pending)(struct kvm_vcpu *vcpu);
void (*triple_fault)(struct kvm_vcpu *vcpu);
int (*get_state)(struct kvm_vcpu *vcpu,
struct kvm_nested_state __user *user_kvm_nested_state,
unsigned user_data_size);

2
arch/x86/kvm/lapic.c
View File

@ -2869,7 +2869,7 @@ void kvm_apic_accept_events(struct kvm_vcpu *vcpu)
return;
if (is_guest_mode(vcpu)) {
r = kvm_x86_ops.nested_ops->check_events(vcpu);
r = kvm_check_nested_events(vcpu);
if (r < 0)
return;
/*

14
arch/x86/kvm/svm/nested.c
View File

@ -661,6 +661,9 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
struct kvm_host_map map;
int rc;
/* Triple faults in L2 should never escape. */
WARN_ON_ONCE(kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu));
rc = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map);
if (rc) {
if (rc == -EINVAL)
@ -782,6 +785,16 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
return 0;
}
static void nested_svm_triple_fault(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
svm->vmcb->control.exit_code = SVM_EXIT_SHUTDOWN;
svm->vmcb->control.exit_info_1 = 0;
svm->vmcb->control.exit_info_2 = 0;
nested_svm_vmexit(svm);
}
int svm_allocate_nested(struct vcpu_svm *svm)
{
struct page *vmcb02_page;
@ -1317,6 +1330,7 @@ out_free:
struct kvm_x86_nested_ops svm_nested_ops = {
.check_events = svm_check_nested_events,
.triple_fault = nested_svm_triple_fault,
.get_nested_state_pages = svm_get_nested_state_pages,
.get_state = svm_get_nested_state,
.set_state = svm_set_nested_state,

9
arch/x86/kvm/vmx/nested.c
View File

@ -4418,6 +4418,9 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
/* trying to cancel vmlaunch/vmresume is a bug */
WARN_ON_ONCE(vmx->nested.nested_run_pending);
/* Similarly, triple faults in L2 should never escape. */
WARN_ON_ONCE(kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu));
kvm_clear_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
/* Service the TLB flush request for L2 before switching to L1. */
@ -4554,6 +4557,11 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
vmx->fail = 0;
}
static void nested_vmx_triple_fault(struct kvm_vcpu *vcpu)
{
nested_vmx_vmexit(vcpu, EXIT_REASON_TRIPLE_FAULT, 0, 0);
}
/*
* Decode the memory-address operand of a vmx instruction, as recorded on an
* exit caused by such an instruction (run by a guest hypervisor).
@ -6590,6 +6598,7 @@ __init int nested_vmx_hardware_setup(int (*exit_handlers[])(struct kvm_vcpu *))
struct kvm_x86_nested_ops vmx_nested_ops = {
.check_events = vmx_check_nested_events,
.hv_timer_pending = nested_vmx_preemption_timer_pending,
.triple_fault = nested_vmx_triple_fault,
.get_state = vmx_get_nested_state,
.set_state = vmx_set_nested_state,
.get_nested_state_pages = vmx_get_nested_state_pages,

29
arch/x86/kvm/x86.c
View File

@ -8329,6 +8329,19 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu)
static_call(kvm_x86_update_cr8_intercept)(vcpu, tpr, max_irr);
}
int kvm_check_nested_events(struct kvm_vcpu *vcpu)
{
if (WARN_ON_ONCE(!is_guest_mode(vcpu)))
return -EIO;
if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
kvm_x86_ops.nested_ops->triple_fault(vcpu);
return 1;
}
return kvm_x86_ops.nested_ops->check_events(vcpu);
}
static void inject_pending_event(struct kvm_vcpu *vcpu, bool *req_immediate_exit)
{
int r;
@ -8374,7 +8387,7 @@ static void inject_pending_event(struct kvm_vcpu *vcpu, bool *req_immediate_exit
* from L2 to L1.
*/
if (is_guest_mode(vcpu)) {
r = kvm_x86_ops.nested_ops->check_events(vcpu);
r = kvm_check_nested_events(vcpu);
if (r < 0)
goto busy;
}
@ -8937,10 +8950,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
goto out;
}
if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
vcpu->mmio_needed = 0;
r = 0;
goto out;
if (is_guest_mode(vcpu)) {
kvm_x86_ops.nested_ops->triple_fault(vcpu);
} else {
vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
vcpu->mmio_needed = 0;
r = 0;
goto out;
}
}
if (kvm_check_request(KVM_REQ_APF_HALT, vcpu)) {
/* Page is swapped out. Do synthetic halt */
@ -9238,7 +9255,7 @@ static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
{
if (is_guest_mode(vcpu))
kvm_x86_ops.nested_ops->check_events(vcpu);
kvm_check_nested_events(vcpu);
return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
!vcpu->arch.apf.halted);

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

@ -56,6 +56,8 @@ static inline unsigned int __shrink_ple_window(unsigned int val,
#define MSR_IA32_CR_PAT_DEFAULT 0x0007040600070406ULL
int kvm_check_nested_events(struct kvm_vcpu *vcpu);
static inline void kvm_clear_exception_queue(struct kvm_vcpu *vcpu)
{
vcpu->arch.exception.pending = false;