[PATCH V4 4/4] KVM: SVM: Raise #UD if VMMCALL instruction is not intercepted

[Kevin Cheng]

The AMD APM states that if VMMCALL instruction is not intercepted, the
instruction raises a #UD exception.

Create a vmmcall exit handler that generates a #UD if a VMMCALL exit
from L2 is being handled by L0, which means that L1 did not intercept
the VMMCALL instruction. The exception to this is if the exiting
instruction was for Hyper-V L2 TLB flush hypercalls as they are handled
by L0.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Kevin Cheng <chengkev@xxxxxxxxxx>
---
 arch/x86/kvm/svm/hyperv.h | 11 +++++++++++
 arch/x86/kvm/svm/nested.c |  4 +---
 arch/x86/kvm/svm/svm.c    | 19 ++++++++++++++++++-
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/hyperv.h b/arch/x86/kvm/svm/hyperv.h
index d3f8bfc05832e..9af03970d40c2 100644
--- a/arch/x86/kvm/svm/hyperv.h
+++ b/arch/x86/kvm/svm/hyperv.h
@@ -41,6 +41,13 @@ static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
 	return hv_vcpu->vp_assist_page.nested_control.features.directhypercall;
 }

+static inline bool nested_svm_is_l2_tlb_flush_hcall(struct kvm_vcpu *vcpu)
+{
+	return guest_hv_cpuid_has_l2_tlb_flush(vcpu) &&
+	       nested_svm_l2_tlb_flush_enabled(vcpu) &&
+	       kvm_hv_is_tlb_flush_hcall(vcpu);
+}
+
 void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);
 #else /* CONFIG_KVM_HYPERV */
 static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu) {}
@@ -48,6 +55,10 @@ static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
 {
 	return false;
 }
+static inline bool nested_svm_is_l2_tlb_flush_hcall(struct kvm_vcpu *vcpu)
+{
+	return false;
+}
 static inline void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu) {}
 #endif /* CONFIG_KVM_HYPERV */

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index de90b104a0dd5..45d1496031a74 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1674,9 +1674,7 @@ int nested_svm_exit_special(struct vcpu_svm *svm)
 	}
 	case SVM_EXIT_VMMCALL:
 		/* Hyper-V L2 TLB flush hypercall is handled by L0 */
-		if (guest_hv_cpuid_has_l2_tlb_flush(vcpu) &&
-		    nested_svm_l2_tlb_flush_enabled(vcpu) &&
-		    kvm_hv_is_tlb_flush_hcall(vcpu))
+		if (nested_svm_is_l2_tlb_flush_hcall(vcpu))
 			return NESTED_EXIT_HOST;
 		break;
 	default:
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f8f9b7a124c36..d662d5ce986ac 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -52,6 +52,7 @@
 #include "svm.h"
 #include "svm_ops.h"

+#include "hyperv.h"
 #include "kvm_onhyperv.h"
 #include "svm_onhyperv.h"

@@ -3258,6 +3259,22 @@ static int bus_lock_exit(struct kvm_vcpu *vcpu)
 	return 0;
 }

+static int vmmcall_interception(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * Per the AMD APM, VMMCALL raises #UD if the VMMCALL intercept
+	 * is not set. For an L2 guest, inject #UD as L1 did not intercept
+	 * VMMCALL, except for Hyper-V L2 TLB flush hypercalls as they
+	 * are handled by L0.
+	 */
+	if (is_guest_mode(vcpu) && !nested_svm_is_l2_tlb_flush_hcall(vcpu)) {
+		kvm_queue_exception(vcpu, UD_VECTOR);
+		return 1;
+	}
+
+	return kvm_emulate_hypercall(vcpu);
+}
+
 static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[SVM_EXIT_READ_CR0]			= cr_interception,
 	[SVM_EXIT_READ_CR3]			= cr_interception,
@@ -3308,7 +3325,7 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[SVM_EXIT_TASK_SWITCH]			= task_switch_interception,
 	[SVM_EXIT_SHUTDOWN]			= shutdown_interception,
 	[SVM_EXIT_VMRUN]			= vmrun_interception,
-	[SVM_EXIT_VMMCALL]			= kvm_emulate_hypercall,
+	[SVM_EXIT_VMMCALL]			= vmmcall_interception,
 	[SVM_EXIT_VMLOAD]			= vmload_interception,
 	[SVM_EXIT_VMSAVE]			= vmsave_interception,
 	[SVM_EXIT_STGI]				= stgi_interception,
--
2.53.0.473.g4a7958ca14-goog