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Re: [PATCH -tip 4/6 V4.1] x86: kprobes checks safeness of insertion address.
- From: Jim Keniston <jkenisto at us dot ibm dot com>
- To: Masami Hiramatsu <mhiramat at redhat dot com>
- Cc: ananth at in dot ibm dot com, Ingo Molnar <mingo at elte dot hu>, LKML <linux-kernel at vger dot kernel dot org>, systemtap-ml <systemtap at sources dot redhat dot com>, kvm at vger dot kernel dot org, Andi Kleen <andi at firstfloor dot org>, Andrew Morton <akpm at linux-foundation dot org>, Arnaldo Carvalho de Melo <acme at redhat dot com>, Steven Rostedt <rostedt at goodmis dot org>, Frederic Weisbecker <fweisbec at gmail dot com>
- Date: Fri, 03 Apr 2009 10:28:06 -0700
- Subject: Re: [PATCH -tip 4/6 V4.1] x86: kprobes checks safeness of insertion address.
- References: <49D4F4E9.2030809@redhat.com> <20090403051854.GA4846@in.ibm.com> <49D63327.8020009@redhat.com>
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