linux-kernel - Re: [PATCH 03/17] perf, x86: Add copy_from_user_nmi

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Message-ID: <501ACB42.6060201@amacapital.net>
Date:	Thu, 02 Aug 2012 11:47:30 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	acme@...hat.com, a.p.zijlstra@...llo.nl, mingo@...e.hu,
	paulus@...ba.org, cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	eranian@...gle.com, gorcunov@...nvz.org, tzanussi@...il.com,
	mhiramat@...hat.com, robert.richter@....com, fche@...hat.com,
	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/17] perf, x86: Add copy_from_user_nmi_nochk for best
 effort copy

On 07/22/2012 05:14 AM, Jiri Olsa wrote:
> Adding copy_from_user_nmi_nochk that provides the best effort
> copy regardless the requesting size crossing the task boundary.
> 
> This is going to be useful for stack dump we need in post
> DWARF CFI based unwind, where we have predefined size of
> the user stack to dump, and we need to store the most of
> the requested dump size, regardless this size is crossing
> the task boundary.

Huh?  This is a TASK_SIZE check, which makes sure that the request
doesn't cross into kernel land.  Otherwise userspace could presumably
read kernel memory by setting bogus values of sp.

--Andy
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