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

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Date:	Fri, 22 Nov 2013 20:46:14 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"Frank Ch. Eigler" <fche@...hat.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>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	virtualization@...ts.linux-foundation.org,
	systemtap@...rceware.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: Re: Re: [PATCH -tip v3 00/23] kprobes: introduce NOKPROBE_SYMBOL()
 and general cleaning of kprobe blacklist

(2013/11/22 11:35), Masami Hiramatsu wrote:
> (2013/11/21 16:29), Ingo Molnar wrote:
>>
>> * Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
>>
>>> (2013/11/21 2:36), Frank Ch. Eigler wrote:
>>
>> [ ... ]
>>>> one needs to resort to something like:
>>>>
>>>> # cat /proc/kallsyms | grep ' [tT] ' | while read addr type symbol; do
>>>>    perf probe $symbol
>>>> done
>>>>
>>>> then wait for a few hours for that to finish. Then, or while the loop
>>>> is still running, run
>>>>
>>>> # perf record -e 'probe:*' -aR sleep 1
>>>>
>>>> to take a kernel down.
>>>
>>> Um, indeed, current blacklist is not perfect. [...]
>>
>> Then it needs to be fixed ASAP!
> 
> OK, I see. At least the two patches included this series
> should be fixed. :)
> 
> And more, I need to test all symbols and drills down.

OK, what I've found was;
 - The functions which can be ftraced look good.
   (see tracing/available_filter_functions)
 - following functions should not be able to be probed.
   - memcpy, memset
   - native_load_sp0 and some other native functions (need to be clear)
   - restore
   - trace_graph_return
   - trace_hardirqs_off_thunk, trace_hardirqs_on_thunk
   - This list still be not perfect. I just enabled/disabled kprobes
     one by one. There might be combined bugs (combination of several
     kprobes).
 - Some of them are hard to specify by NOKPROBE_SYMBOL because they are
   defined in assembly file.

Anyway, to fix all of them, I think we need file-based blacklist
especially for assembler symbols.

For example, we can get all text symbols by below command;
 nm some-file.o | grep -i " t " | cut -f3 -d" "
so that we can make a blacklisted-symbol list for the file.
I need to look the Kbuild for how I can do that in Makefile.

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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