[patch] s390 kprobe fix instruction length calculation

[patch] s390 kprobe fix instruction length calculation

[David Wilder]

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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.




[-- Attachment #2: s390_kprobes_ilen.patch --]
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 arch/s390/kernel/kprobes.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index 358d2bb..e40373d 100644
--- 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;

Re: [patch] s390 kprobe fix instruction length calculation

[Heiko Carstens]

On Wed, Aug 15, 2007 at 02:31:40PM -0700, David Wilder wrote:
> 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.
>
>  	/* save the instruction length (pop 5-5) in bytes */
> -	switch (*(__u8 *) (ainsn->insn) >> 4) {
> +	switch (*(__u8 *) (ainsn->insn) >> 6) {
>  	case 0:

Added to the s390 patch queue. Thanks! :)