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:	Wed, 27 Nov 2013 14:30:45 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
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


* Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> (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.

assembler symbols shouldn't be particular hard either, just put them 
into the noprobes section.

> 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.

I think it's generally better to add explicit annotations to the code.

Thanks,

	Ingo
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