[PATCH 31/45] KVM: x86: "Handle" failed decode when skipping instructions

[Paolo Bonzini]

When calling into the emulator to skip an instruction, the caller has
already performed the side effects of the instruction and cannot
propagate -EFAULT.  Mark the VM dead.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/svm/svm.c |  9 +++++++--
 arch/x86/kvm/vmx/vmx.c | 10 +++++++---
 arch/x86/kvm/x86.c     |  4 ++--
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 205d8783aa13..2601f8359137 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -304,6 +304,7 @@ static int __svm_skip_emulated_instruction(struct kvm_vcpu *vcpu,
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	unsigned long old_rflags;
+	int r;
 
 	/*
 	 * SEV-ES does not expose the next RIP. The RIP update is controlled by
@@ -321,7 +322,10 @@ static int __svm_skip_emulated_instruction(struct kvm_vcpu *vcpu,
 		if (unlikely(!commit_side_effects))
 			old_rflags = svm->vmcb->save.rflags;
 
-		if (!kvm_emulate_instruction(vcpu, emul_type))
+		r = kvm_emulate_instruction(vcpu, emul_type);
+		if (r < 0)
+			kvm_vm_dead(vcpu->kvm);
+		if (r <= 0)
 			return 0;
 
 		if (unlikely(!commit_side_effects))
@@ -2128,7 +2132,8 @@ static int icebp_interception(struct kvm_vcpu *vcpu)
 	 * instead of after it (and SVM doesn't provide enough information for
 	 * KVM to detect and manually advance the pre-#DB RIP).
 	 */
-	svm_skip_emulated_instruction(vcpu);
+	if (!svm_skip_emulated_instruction(vcpu))
+		return 0;
 	kvm_queue_exception(vcpu, DB_VECTOR);
 	return 1;
 }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 80dfb3c6268b..27cb0d64fb5c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1809,6 +1809,7 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	union vmx_exit_reason exit_reason = vt_get_exit_reason(vcpu);
 	unsigned long rip, orig_rip;
 	u32 instr_len;
+	int r;
 
 	/*
 	 * Using VMCS.VM_EXIT_INSTRUCTION_LEN on EPT misconfig depends on
@@ -1857,7 +1858,10 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
 #endif
 		kvm_rip_write(vcpu, rip);
 	} else {
-		if (!kvm_emulate_instruction(vcpu, EMULTYPE_SKIP))
+		r = kvm_emulate_instruction(vcpu, EMULTYPE_SKIP);
+		if (r < 0)
+			kvm_vm_dead(vcpu->kvm);
+		if (r <= 0)
 			return 0;
 	}
 
@@ -5538,8 +5542,8 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 			 * higher priority.  Note, skipping ICEBP still clears
 			 * STI and MOVSS blocking.
 			 */
-			if (is_icebp(intr_info))
-				WARN_ON(!skip_emulated_instruction(vcpu));
+			if (is_icebp(intr_info) && !skip_emulated_instruction(vcpu))
+				return 0;
 
 			kvm_queue_exception_p(vcpu, DB_VECTOR, dr6);
 			return 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5f7f87ff4d17..5818101d1d8a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6235,8 +6235,8 @@ int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	int r;
 
 	r = kvm_x86_call(skip_emulated_instruction)(vcpu);
-	if (unlikely(!r))
-		return 0;
+	if (unlikely(r <= 0))
+		return r;
 
 	kvm_pmu_instruction_retired(vcpu);
 
-- 
2.52.0