linux-kernel - Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE

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Date:	Thu, 5 Dec 2013 18:38:04 +0530
From:	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	x86@...nel.org, lkml <linux-kernel@...r.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	systemtap@...rceware.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v4 0/6] kprobes: introduce NOKPROBE_SYMBOL() and
 fixes crash bugs

> OK, I think the kprobe is like a strong medicine, not a toy,
> since it can intercept most of the kernel functions which
> may process a sensitive user private data. Thus even if we
> fix all bugs and make it safe, I don't think we can open
> it for all users (of course, there should be a knob to open
> for any or restricted users.)
>
>> So we need both a maintainable and a sane/safe solution, and I'd like
>> to apply the whole thing at once and be at ease that the solution is
>> round. We should have done this years ago.
>
> For the safeness of kprobes, I have an idea; introduce a whitelist
> for dynamic events. AFAICS, the biggest unstable issue of kprobes
> comes from putting *many* probes on the functions called from tracers.
>
> It doesn't crash the kernel but slows down so much, because every
> probes hit many other nested miss-hit probes. This gives us a big
> performance impact. However, on the other side, this kind of feature
> can be used *for debugging* static trace events by dynamic one if we
> carefully use a small number of probes on such functions. :)
>
> Thus, I think we can restrict users from probing such functions by
> using a whitelist which ftrace does already have;
>  available_filter_functions :)
I am not sure if this question is related, uprobes or ftrace code does
not  define __kprobes, so is it safe to place kprobe on uprobes or
ftrace code? Is it expected from arch code to support such cases?

Thanks,
Sandeepa
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