KVM: Fix emulate_sys[call, enter, exit]()'s fault handling

This patch fixes emulate_syscall(), emulate_sysenter() and
emulate_sysexit() to handle injected faults properly.

Even though original code injects faults in these functions,
we cannot handle these unless we use the different return
value from the UNHANDLEABLE case. So this patch use X86EMUL_*
codes instead of -1 and 0 and makes x86_emulate_insn() to
handle these propagated faults.

Be sure that, in x86_emulate_insn(), goto cannot_emulate and
goto done with rc equals X86EMUL_UNHANDLEABLE have same effect.
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/emulate.c

@@ -1599,7 +1599,7 @@ emulate_syscall(struct x86_emulate_ctxt *ctxt)
 
 	/* syscall is not available in real mode */
 	if (ctxt->mode == X86EMUL_MODE_REAL || ctxt->mode == X86EMUL_MODE_VM86)
-		return -1;
+		return X86EMUL_UNHANDLEABLE;
 
 	setup_syscalls_segments(ctxt, &cs, &ss);
 
@@ -1636,7 +1636,7 @@ emulate_syscall(struct x86_emulate_ctxt *ctxt)
 		ctxt->eflags &= ~(EFLG_VM | EFLG_IF | EFLG_RF);
 	}
 
-	return 0;
+	return X86EMUL_CONTINUE;
 }
 
 static int
@@ -1649,14 +1649,14 @@ emulate_sysenter(struct x86_emulate_ctxt *ctxt)
 	/* inject #GP if in real mode */
 	if (ctxt->mode == X86EMUL_MODE_REAL) {
 		kvm_inject_gp(ctxt->vcpu, 0);
-		return -1;
+		return X86EMUL_UNHANDLEABLE;
 	}
 
 	/* XXX sysenter/sysexit have not been tested in 64bit mode.
 	* Therefore, we inject an #UD.
 	*/
 	if (ctxt->mode == X86EMUL_MODE_PROT64)
-		return -1;
+		return X86EMUL_UNHANDLEABLE;
 
 	setup_syscalls_segments(ctxt, &cs, &ss);
 
@@ -1665,13 +1665,13 @@ emulate_sysenter(struct x86_emulate_ctxt *ctxt)
 	case X86EMUL_MODE_PROT32:
 		if ((msr_data & 0xfffc) == 0x0) {
 			kvm_inject_gp(ctxt->vcpu, 0);
-			return -1;
+			return X86EMUL_PROPAGATE_FAULT;
 		}
 		break;
 	case X86EMUL_MODE_PROT64:
 		if (msr_data == 0x0) {
 			kvm_inject_gp(ctxt->vcpu, 0);
-			return -1;
+			return X86EMUL_PROPAGATE_FAULT;
 		}
 		break;
 	}
@@ -1696,7 +1696,7 @@ emulate_sysenter(struct x86_emulate_ctxt *ctxt)
 	kvm_x86_ops->get_msr(ctxt->vcpu, MSR_IA32_SYSENTER_ESP, &msr_data);
 	c->regs[VCPU_REGS_RSP] = msr_data;
 
-	return 0;
+	return X86EMUL_CONTINUE;
 }
 
 static int
@@ -1711,7 +1711,7 @@ emulate_sysexit(struct x86_emulate_ctxt *ctxt)
 	if (ctxt->mode == X86EMUL_MODE_REAL ||
 	    ctxt->mode == X86EMUL_MODE_VM86) {
 		kvm_inject_gp(ctxt->vcpu, 0);
-		return -1;
+		return X86EMUL_UNHANDLEABLE;
 	}
 
 	setup_syscalls_segments(ctxt, &cs, &ss);
@@ -1729,7 +1729,7 @@ emulate_sysexit(struct x86_emulate_ctxt *ctxt)
 		cs.selector = (u16)(msr_data + 16);
 		if ((msr_data & 0xfffc) == 0x0) {
 			kvm_inject_gp(ctxt->vcpu, 0);
-			return -1;
+			return X86EMUL_PROPAGATE_FAULT;
 		}
 		ss.selector = (u16)(msr_data + 24);
 		break;
@@ -1737,7 +1737,7 @@ emulate_sysexit(struct x86_emulate_ctxt *ctxt)
 		cs.selector = (u16)(msr_data + 32);
 		if (msr_data == 0x0) {
 			kvm_inject_gp(ctxt->vcpu, 0);
-			return -1;
+			return X86EMUL_PROPAGATE_FAULT;
 		}
 		ss.selector = cs.selector + 8;
 		cs.db = 0;
@@ -1753,7 +1753,7 @@ emulate_sysexit(struct x86_emulate_ctxt *ctxt)
 	c->eip = ctxt->vcpu->arch.regs[VCPU_REGS_RDX];
 	c->regs[VCPU_REGS_RSP] = ctxt->vcpu->arch.regs[VCPU_REGS_RCX];
 
-	return 0;
+	return X86EMUL_CONTINUE;
 }
 
 static bool emulator_bad_iopl(struct x86_emulate_ctxt *ctxt)
@@ -2476,8 +2476,9 @@ twobyte_insn:
 		}
 		break;
 	case 0x05: 		/* syscall */
-		if (emulate_syscall(ctxt) == -1)
-			goto cannot_emulate;
+		rc = emulate_syscall(ctxt);
+		if (rc != X86EMUL_CONTINUE)
+			goto done;
 		else
 			goto writeback;
 		break;
@@ -2548,14 +2549,16 @@ twobyte_insn:
 		c->dst.type = OP_NONE;
 		break;
 	case 0x34:		/* sysenter */
-		if (emulate_sysenter(ctxt) == -1)
-			goto cannot_emulate;
+		rc = emulate_sysenter(ctxt);
+		if (rc != X86EMUL_CONTINUE)
+			goto done;
 		else
 			goto writeback;
 		break;
 	case 0x35:		/* sysexit */
-		if (emulate_sysexit(ctxt) == -1)
-			goto cannot_emulate;
+		rc = emulate_sysexit(ctxt);
+		if (rc != X86EMUL_CONTINUE)
+			goto done;
 		else
 			goto writeback;
 		break;