linux-kernel - Re: brk randomization breaks columns

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Date:	Mon, 4 Feb 2008 14:01:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Pavel Machek <pavel@....cz>
Cc:	jikos@...e.cz, kernel list <linux-kernel@...r.kernel.org>
Subject: Re: brk randomization breaks columns


* Pavel Machek <pavel@....cz> wrote:

> Hmm, code in binfmt_elf is really strange.
> 
>         elf_bss += load_bias;
>         elf_brk += load_bias;
>         start_code += load_bias;
>         end_code += load_bias;
>         start_data += load_bias;
>         end_data += load_bias;
> 
>         /* Calling set_brk effectively mmaps the pages that we need
>          * for the bss and break sections.  We must do this before
>          * mapping in the interpreter, to make sure it doesn't wind
>          * up getting placed where the bss needs to go.
>          */
>         retval = set_brk(elf_bss, elf_brk);
> 
> ... so we allocate non-randoimzed brk, but later we just overwrite bss 
> variable with new, shiner and better randomized value... without 
> unmapping the old one... The code in binfmt_elf.c is really a mess.

hm, so it seems that it isnt even the randomization that causes the 
problem - but somehow the randomization code itself is broken, right? 

Would you be interested in figuring out how to unbreak this? [if not, 
could you send me the binary?]

	Ingo
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