x86: kprobes bugfix

Kprobes for x86-64 may cause a kernel crash if it inserted on "iret"
instruction. "call absolute" is invalid on x86-64, so we don't need
treat it.

 - Change the processing order as same as x86-32.
 - Add "iret"(0xcf) case.
 - Remove next_rip local variable.
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/kprobes_64.c

@@ -485,7 +485,6 @@ static void __kprobes resume_execution(struct kprobe *p,
 		struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 {
 	unsigned long *tos = (unsigned long *)regs->rsp;
-	unsigned long next_rip = 0;
 	unsigned long copy_rip = (unsigned long)p->ainsn.insn;
 	unsigned long orig_rip = (unsigned long)p->addr;
 	kprobe_opcode_t *insn = p->ainsn.insn;
@@ -494,46 +493,42 @@ static void __kprobes resume_execution(struct kprobe *p,
 	if (*insn >= 0x40 && *insn <= 0x4f)
 		insn++;
 
+	regs->eflags &= ~TF_MASK;
 	switch (*insn) {
 	case 0x9c:	/* pushfl */
 		*tos &= ~(TF_MASK | IF_MASK);
 		*tos |= kcb->kprobe_old_rflags;
 		break;
-	case 0xc3:		/* ret/lret */
-	case 0xcb:
-	case 0xc2:
+	case 0xc2:	/* iret/ret/lret */
+	case 0xc3:
 	case 0xca:
-		regs->eflags &= ~TF_MASK;
-		/* rip is already adjusted, no more changes required*/
-		return;
+	case 0xcb:
+	case 0xcf:
+	case 0xea:	/* jmp absolute -- ip is correct */
+		/* ip is already adjusted, no more changes required */
+		goto no_change;
 	case 0xe8:	/* call relative - Fix return addr */
 		*tos = orig_rip + (*tos - copy_rip);
 		break;
 	case 0xff:
 		if ((insn[1] & 0x30) == 0x10) {
 			/* call absolute, indirect */
-			/* Fix return addr; rip is correct. */
-			next_rip = regs->rip;
+			/* Fix return addr; ip is correct. */
 			*tos = orig_rip + (*tos - copy_rip);
+			goto no_change;
 		} else if (((insn[1] & 0x31) == 0x20) ||	/* jmp near, absolute indirect */
 			   ((insn[1] & 0x31) == 0x21)) {	/* jmp far, absolute indirect */
-			/* rip is correct. */
-			next_rip = regs->rip;
+			/* ip is correct. */
+			goto no_change;
 		}
-		break;
-	case 0xea:		/* jmp absolute -- rip is correct */
-		next_rip = regs->rip;
-		break;
 	default:
 		break;
 	}
 
-	regs->eflags &= ~TF_MASK;
-	if (next_rip) {
-		regs->rip = next_rip;
-	} else {
 	regs->rip = orig_rip + (regs->rip - copy_rip);
-	}
+no_change:
+
+	return;
 }
 
 int __kprobes post_kprobe_handler(struct pt_regs *regs)