Commit cb6a32c2 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210302174515.2812275-2-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 63129754

arch/x86/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/lapic.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

		/*

arch/x86/kvm/svm/nested.c

+14 −0
Original line number Diff line number Diff line
@@ -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 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, 


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,

arch/x86/kvm/vmx/nested.c

+9 −0
Original line number Diff line number Diff line
@@ -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,

arch/x86/kvm/x86.c

+23 −6
Original line number Diff line number Diff line
@@ -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;

	}
@@ -8937,11 +8950,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) 
			goto out;

		}

		if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {

			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 */

			vcpu->arch.apf.halted = true;
@@ -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);