[patch 09/10] kprobes: fix instruction length calculation

Martin Schwidefsky
2007-08-22T12:36:19Z

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From: David Wilder <dwilder@us.ibm.com>

Placing a kprobe on "bc" instruction (s390/s390x) can cause an oops.
The instruction length is encoded into the first two bits of the s390
instruction. Kprobe is incorrectly computing the instruction length.
The instruction length is used for determining what type of "fix-up" is
needed for conditional branch instruction. The problem can bee seen by
placing a kprobe on a "bc" instruction that will not branch. The
results is that Kprobe incorrectly computes the new instruction
pointer (psw.addr) after single stepping the instruction. The problem
is corrected with this patch.

Signed-off-by: David Wilder <dwilder@us.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---

arch/s390/kernel/kprobes.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Index: quilt-2.6/arch/s390/kernel/kprobes.c
===================================================================
--- quilt-2.6.orig/arch/s390/kernel/kprobes.c
+++ quilt-2.6/arch/s390/kernel/kprobes.c
@@ -85,7 +85,7 @@ void __kprobes get_instruction_type(stru
ainsn->reg = (*ainsn->insn & 0xf0) >> 4;

/* save the instruction length (pop 5-5) in bytes */
- switch (*(__u8 *) (ainsn->insn) >> 4) {
+ switch (*(__u8 *) (ainsn->insn) >> 6) {
case 0:
ainsn->ilen = 2;
break;