Re: [PATCH -tip 4/6 V4.1] x86: kprobes checks safeness of insertion address.

Masami Hiramatsu
2009-04-03T19:20:06Z

Jim Keniston wrote:
> On Fri, 2009-04-03 at 12:02 -0400, Masami Hiramatsu wrote:
>> Ensure safeness of inserting kprobes by checking whether the specified
>> address is at the first byte of a instruction. This is done by decoding
>> probed function from its head to the probe point.
>>
>> changes from v4:
>> - change a comment according to Ananth's suggestion.
>>
>> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
>> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
>> Cc: Jim Keniston <jkenisto@us.ibm.com>
>> Cc: Ingo Molnar <mingo@elte.hu>
>> ---
>>
>> arch/x86/kernel/kprobes.c | 51 +++++++++++++++++++++++++++++++++++++++++++++
>> 1 files changed, 51 insertions(+), 0 deletions(-)
>>
>>
>> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
> ...
>> +/* Recover original instruction */
>
> /* Recover the probed instruction at addr for further analysis. */
> See below.

Sure.

>
>> +static int recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
>> +{
>> + struct kprobe *kp;
>> + kp = get_kprobe((void *)addr);
>> + if (!kp)
>> + return -EINVAL;
>> +
>> + /* Don't use p->ainsn.insn; which will be modified by fix_riprel */
>
> fix_riprel doesn't affect the instruction's length, which is what
> concerns this patch. But we want this function to be useful for
> unforeseen uses as well, so I like the code you have. Just consider the
> suggested comment changes.
>
> /*
> * Don't use p->ainsn.insn, which could be modified -- e.g.,
> * by fix_riprel().
> */

Thanks, I'll update comments then!

>
>> + memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
>> + buf[0] = kp->opcode;
>> + return 0;
>> +}
>
> Jim Keniston
>
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