[PATCH RFC] KVM: inject #UD if instruction emulation fails while vcpu is in cpl==3

[Gleb Natapov <gleb@redhat.com>]

Do not kill VM If instruction emulation fails while vcpu is in
userspace. Inject #UD instead in a hope that guest OS will kill offending
process. Emulation failure is still traced by ftrace point to help
analyze the problem.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
---

This patch goes on top of previous patchset.

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ed48904..5aa0944 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -575,7 +575,6 @@ enum emulation_result {
 #define EMULTYPE_SKIP		    (1 << 2)
 int emulate_instruction(struct kvm_vcpu *vcpu,
 			unsigned long cr2, u16 error_code, int emulation_type);
-void kvm_report_emulation_failure(struct kvm_vcpu *cvpu, const char *context);
 void realmode_lgdt(struct kvm_vcpu *vcpu, u16 size, unsigned long address);
 void realmode_lidt(struct kvm_vcpu *vcpu, u16 size, unsigned long address);
 
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index ddfa865..4ddcb1b 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2776,11 +2776,8 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code)
 		return 1;
 	case EMULATE_DO_MMIO:
 		++vcpu->stat.mmio_exits;
-		return 0;
+		/* fall through */
 	case EMULATE_FAIL:
-		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
-		vcpu->run->internal.ndata = 0;
 		return 0;
 	default:
 		BUG();
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 889f660..b2eed27 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1449,7 +1449,7 @@ static int io_interception(struct vcpu_svm *svm)
 	string = (io_info & SVM_IOIO_STR_MASK) != 0;
 	in = (io_info & SVM_IOIO_TYPE_MASK) != 0;
 	if (string || in)
-		return !(emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DO_MMIO);
+		return emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DONE;
 
 	port = io_info >> 16;
 	size = (io_info & SVM_IOIO_SIZE_MASK) >> SVM_IOIO_SIZE_SHIFT;
@@ -2297,16 +2297,12 @@ static int iret_interception(struct vcpu_svm *svm)
 
 static int invlpg_interception(struct vcpu_svm *svm)
 {
-	if (emulate_instruction(&svm->vcpu, 0, 0, 0) != EMULATE_DONE)
-		pr_unimpl(&svm->vcpu, "%s: failed\n", __func__);
-	return 1;
+	return emulate_instruction(&svm->vcpu, 0, 0, 0) == EMULATE_DONE;
 }
 
 static int emulate_on_interception(struct vcpu_svm *svm)
 {
-	if (emulate_instruction(&svm->vcpu, 0, 0, 0) != EMULATE_DONE)
-		pr_unimpl(&svm->vcpu, "%s: failed\n", __func__);
-	return 1;
+	return emulate_instruction(&svm->vcpu, 0, 0, 0) == EMULATE_DONE;
 }
 
 static int cr8_write_interception(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 875b785..d05bc46 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3003,7 +3003,7 @@ static int handle_io(struct kvm_vcpu *vcpu)
 	++vcpu->stat.io_exits;
 
 	if (string || in)
-		return !(emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DO_MMIO);
+		return emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DONE;
 
 	port = exit_qualification >> 16;
 	size = (exit_qualification & 7) + 1;
@@ -3260,22 +3260,7 @@ static int handle_wbinvd(struct kvm_vcpu *vcpu)
 
 static int handle_apic_access(struct kvm_vcpu *vcpu)
 {
-	unsigned long exit_qualification;
-	enum emulation_result er;
-	unsigned long offset;
-
-	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
-	offset = exit_qualification & 0xffful;
-
-	er = emulate_instruction(vcpu, 0, 0, 0);
-
-	if (er !=  EMULATE_DONE) {
-		printk(KERN_ERR
-		       "Fail to handle apic access vmexit! Offset is 0x%lx\n",
-		       offset);
-		return -ENOEXEC;
-	}
-	return 1;
+	return emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DONE;
 }
 
 static int handle_task_switch(struct kvm_vcpu *vcpu)
@@ -3487,13 +3472,8 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
 			goto out;
 		}
 
-		if (err != EMULATE_DONE) {
-			vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-			vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
-			vcpu->run->internal.ndata = 0;
-			ret = 0;
-			goto out;
-		}
+		if (err != EMULATE_DONE)
+			return 0;
 
 		if (signal_pending(current))
 			goto out;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 299b602..9be8b84 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3577,24 +3577,6 @@ int emulator_set_dr(int dr, unsigned long value, struct kvm_vcpu *vcpu)
 	return __kvm_set_dr(vcpu, dr, value);
 }
 
-void kvm_report_emulation_failure(struct kvm_vcpu *vcpu, const char *context)
-{
-	u8 opcodes[4];
-	unsigned long rip = kvm_rip_read(vcpu);
-	unsigned long rip_linear;
-
-	if (!printk_ratelimit())
-		return;
-
-	rip_linear = rip + get_segment_base(vcpu, VCPU_SREG_CS);
-
-	kvm_read_guest_virt(rip_linear, (void *)opcodes, 4, vcpu, NULL);
-
-	printk(KERN_ERR "emulation failed (%s) rip %lx %02x %02x %02x %02x\n",
-	       context, rip, opcodes[0], opcodes[1], opcodes[2], opcodes[3]);
-}
-EXPORT_SYMBOL_GPL(kvm_report_emulation_failure);
-
 static u64 mk_cr_64(u64 curr_cr, u32 new_val)
 {
 	return (curr_cr & ~((1ULL << 32) - 1)) | new_val;
@@ -3801,6 +3783,27 @@ static void inject_emulated_exception(struct kvm_vcpu *vcpu)
 		kvm_queue_exception(vcpu, ctxt->exception);
 }
 
+static int handle_emulation_failure(struct kvm_vcpu *vcpu)
+{
+	struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
+
+	++vcpu->stat.insn_emulation_fail;
+	trace_kvm_emulate_insn_failed(vcpu);
+	if (ctxt->cpl != 3) {
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
+		return EMULATE_FAIL;
+	} else {
+		/*
+		 * if emulation failed in userspace inject #UD
+		 * instead of killing VM
+		 */
+		kvm_queue_exception(vcpu, UD_VECTOR);
+		return EMULATE_DONE;
+	}
+}
+
 int emulate_instruction(struct kvm_vcpu *vcpu,
 			unsigned long cr2,
 			u16 error_code,
@@ -3869,11 +3872,11 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 
 		++vcpu->stat.insn_emulation;
 		if (r)  {
-			++vcpu->stat.insn_emulation_fail;
-			trace_kvm_emulate_insn_failed(vcpu);
 			if (kvm_mmu_unprotect_page_virt(vcpu, cr2))
 				return EMULATE_DONE;
-			return EMULATE_FAIL;
+			if (emulation_type & EMULTYPE_SKIP)
+				return EMULATE_FAIL;
+			return handle_emulation_failure(vcpu);
 		}
 	}
 
@@ -3898,9 +3901,7 @@ restart:
 		if (kvm_mmu_unprotect_page_virt(vcpu, cr2))
 			return EMULATE_DONE;
 
-		trace_kvm_emulate_insn_failed(vcpu);
-		kvm_report_emulation_failure(vcpu, "mmio");
-		return EMULATE_FAIL;
+		return handle_emulation_failure(vcpu);
 	}
 
 	toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
@@ -4734,7 +4735,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 		r = emulate_instruction(vcpu, 0, 0, EMULTYPE_NO_DECODE);
 		srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
-		if (r == EMULATE_DO_MMIO) {
+		if (r != EMULATE_DONE) {
 			r = 0;
 			goto out;
 		}
--
			Gleb.