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

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Date:	Fri, 03 Apr 2009 10:28:06 -0700
From:	Jim Keniston <jkenisto@...ibm.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	ananth@...ibm.com, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	systemtap-ml <systemtap@...rces.redhat.com>, kvm@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH -tip 4/6 V4.1] x86: kprobes checks safeness of
	insertion address.

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@...hat.com>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Jim Keniston <jkenisto@...ibm.com>
> Cc: Ingo Molnar <mingo@...e.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

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