linux-kernel - Re: brk randomization breaks columns

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Message-ID: <Pine.LNX.4.64.0802041528470.30955@jikos.suse.cz>
Date:	Mon, 4 Feb 2008 15:33:18 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: brk randomization breaks columns

On Mon, 4 Feb 2008, Ingo Molnar wrote:

> 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?]

I still don't seem to fully understand what is happening here -- aparently 
this is triggerable only with old programs linked against libc.so.5, and I 
am not able to trigger it with my trivial program when I link it against 
old libc.so.5, which just basically does brk() and checks whether 
/proc/<pid>/maps are OK. Seems to me that (at least certain versions) of 
libc.so.5 (wrongly) assume that end of the bss is the start of the heap, 
but I will try to investigate it more.

Ingo, the code in commit c1d171a0029 is IMHO funcionalli identical to 
your exec-shield in fedora kernels, so even libc.so.5-linked binaries on 
any Fedora distro should trigger this bug ... (or you can use the binary 
that Pavel supplied). Haven't tried this yet.

Thanks,

-- 
Jiri Kosina
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