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

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Message-ID: <20120803111255.GB937@krava.brq.redhat.com>
Date:	Fri, 3 Aug 2012 13:12:55 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
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
Subject: Re: [PATCH 03/17] perf, x86: Add copy_from_user_nmi_nochk for best
 effort copy

On Thu, Aug 02, 2012 at 11:47:30AM -0700, Andy Lutomirski wrote:
> 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.

haven't realized that..  new version won't have this

thanks,
jirka
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