[S390] kprobes: fix instruction length calculation

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>

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index 358d2bbbc48105854d67fac55c33f2ce943bbbb0..e40373d9fbce7ba975f3cbba412c70368988273d 100644 (file)
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -85,7 +85,7 @@ void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
        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;