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

Jim Keniston
2009-04-03T17:28:06Z

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.

> +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().
*/

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

Jim Keniston