[PATCH] kprobes: bad manipulation of 2 byte opcode on x86_64

Problem:

If we put a probe onto a callq instruction and the probe is executed,
kernel panic of Bad RIP value occurs.

Root cause:

If resume_execution() found 0xff at first byte of p->ainsn.insn, it must
check the _second_ byte.  But current resume_execution check _first_ byte
again.

I changed it checks second byte of p->ainsn.insn.

Kprobes on i386 don't have this problem, because the implementation is a
little bit different from x86_64.

Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Satoshi Oshima <soshima@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/kprobes.c

@@ -514,13 +514,13 @@ static void __kprobes resume_execution(struct kprobe *p,
 		*tos = orig_rip + (*tos - copy_rip);
 		break;
 	case 0xff:
-		if ((*insn & 0x30) == 0x10) {
+		if ((insn[1] & 0x30) == 0x10) {
 			/* call absolute, indirect */
 			/* Fix return addr; rip is correct. */
 			next_rip = regs->rip;
 			*tos = orig_rip + (*tos - copy_rip);
-		} else if (((*insn & 0x31) == 0x20) ||	/* jmp near, absolute indirect */
-			   ((*insn & 0x31) == 0x21)) {	/* jmp far, absolute indirect */
+		} 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;
 		}