linux-kernel - Re: Re: Re: Re: Re: [PATCH RFC 2/6] arm64: Kprobes with single stepping support

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Message-ID: <52823728.1070003@hitachi.com>
Date:	Tue, 12 Nov 2013 23:11:52 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>
Cc:	Will Deacon <will.deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"steve.capper@...aro.org" <steve.capper@...aro.org>,
	"nico@...aro.org" <nico@...aro.org>,
	"srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"Vijaya.Kumar@...iumnetworks.com" <Vijaya.Kumar@...iumnetworks.com>,
	Jiang Liu <liuj97@...il.com>,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: Re: Re: Re: Re: [PATCH RFC 2/6] arm64: Kprobes with single
 stepping support

(2013/11/12 19:55), Sandeepa Prabhu wrote:
>>>>> Thanks for steps, ARM64 ftrace patches are under review on arm mailing
>>>>> list, I can contact the (linaro) developer implementing ftrace on
>>>>> what's supported and then figure-out a way to test this concurrency of
>>>>> kprobes breakpoint and hardware breakpoint.
>>>>
>>>> Would you mean this? :)
>>>> http://www.spinics.net/lists/arm-kernel/msg278477.html
>>>>
>>>> Wow, it seems that this also has some works around instruction
>>>> manipulation (and confusable filenames...)
>>> I referred to: http://lwn.net/Articles/572323/  which is another
>>> implementation and on LAKML
>>
>> OK, I'll check that (and looks good at a glance).
>> By the way, I concern about Linaro guys who looks working a bit far
>> from the LKML and original feature maintainers. Please contact them,
>> I'm sure they don't bite your hand :)
> Hmm sure, will convey to our developers/leads :-)

Nice :)

>> BTW, I'm currently trying a general housecleaning of __kprobes
>> annotations. It may also have impact on your patch.
>> https://lkml.org/lkml/2013/11/8/187
> Hmm, we can help testing your patchset on arm64 platforms. Also have
> many doubts on the changes you are working [blacklisting probes etc]
> 
> Basically I had tried placing kprobe on memcpy() and the model hung
> (insmod never returned back!). Fast-model I have does not have option
> of any debug so no clue what happened!.

On x86, I can probe memcpy() safely. It depends on the kprobes (and
breakpoint handling) implementation, and it could be found.

> memcpy() is low-level call being used internally within kprobes, so
> probably we cannot handle probe on that routine, but then how to make
> sure all such API are rejected by kprobe sub-system ?

I see, the blacklist still needs to be maintained. I periodically
run a test for probing each function on my kernel, and if I found
such problem, I added it on the blacklist.
Currently I run the test only on x86, so perhaps, other arch does
not have well tested yet.

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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