linux-kernel - Re: [PATCH -tip v3 00/23] kprobes: introduce NOKPROBE_SYMBOL() and general cleaning of kprobe blacklist

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Message-ID: <528CFAED.1000703@redhat.com>
Date:	Wed, 20 Nov 2013 10:09:49 -0800
From:	Josh Stone <jistone@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
CC:	Ingo Molnar <mingo@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-arch@...r.kernel.org,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>, x86@...nel.org,
	lkml <linux-kernel@...r.kernel.org>,
	virtualization@...ts.linux-foundation.org,
	systemtap@...rceware.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v3 00/23] kprobes: introduce NOKPROBE_SYMBOL() and
 general cleaning of kprobe blacklist

On 11/20/2013 09:56 AM, Steven Rostedt wrote:
> On Wed, 20 Nov 2013 12:36:00 -0500
> "Frank Ch. Eigler" <fche@...hat.com> wrote:
> 
>> Hi -
>>
>>>> Does this new blacklist cover enough that the kernel now survives a 
>>>> broadly wildcarded perf-probe, e.g. over e.g. all of its kallsyms?
>>>
>>> That's generally the purpose of the annotations - if it doesn't then 
>>> that's a bug.
>>
>> AFAIK, no kernel since kprobes was introduced has ever stood up to
>> that test.  perf probe lacks the wildcarding powers of systemtap, so
>> one needs to resort to something like:
>>
>> # cat /proc/kallsyms | grep ' [tT] ' | while read addr type symbol; do
>>    perf probe $symbol
>> done
> 
> I'm curious to why one would do that. IIUC, perf now has function
> tracing support.

Then consider something like probing all inline "call" sites, which will
be sprinkled in the middle where ftrace doesn't apply.

The point is not whether there's an alternative - kprobes really ought
to be wholly safe regardless.  Slow, if you did such broad probing,
sure, but still safe.

And a real use-case probably wouldn't probe *all* functions/inlines, but
it illustrates that there are at least a few in the full set that don't
behave well.
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