linux-kernel - Re: [PATCH c/r -mm] c/r: prctl: Simplify PR_SET

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Message-ID: <4F8D9B06.109@parallels.com>
Date:	Tue, 17 Apr 2012 20:32:06 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Kees Cook <keescook@...omium.org>
CC:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH c/r -mm] c/r: prctl: Simplify PR_SET_MM on mm::code/data
 assignment

On 04/17/2012 08:26 PM, Kees Cook wrote:
> On Mon, Apr 16, 2012 at 3:55 PM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
>> The mm::start_code, end_code, start_data, end_data members
>> are set during startup of executable file and are not changed
>> after.
>>
>> But the program itself might map new executable or/and data areas in
>> time so the original values written into mm fields mentioned above
>> might not have correspond VMA area at all, thus if one try to
>> use this prctl codes without underlied VMA, the error will be
>> returned.
> 
> Hrm, what is the utility of these fields then? If they're not "real",
> should the kernel even bother tracking it at all? (Or, should it be
> fixed to actually do something useful?)

As far as I see these values are used by aout binfmt core-dumping code
and in flat relocations load. Elf doesn't read either of them, just loads.

> -Kees
> 

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