linux-kernel - Re: brk randomization breaks columns

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Message-ID: <20080204202527.GD4915@elf.ucw.cz>
Date:	Mon, 4 Feb 2008 21:25:27 +0100
From:	Pavel Machek <pavel@....cz>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Ingo Molnar <mingo@...e.hu>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: brk randomization breaks columns

Hi!

> > Not sure this helps... If I only randomize _end_ of heap, it still 
> > works. If I try to randomize beggining of heap, too, it will not even 
> > start recent binaries :-(.
> 
> I don't uderstand this, sorry. Ehen the mapping for the new process is 
> being established during loading of the binary, the beginning and the end 
> of the heap are the same ...

Okay, I was assuming this is mapping heap..

  /* 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);

If I add

+       elf_brk += random;

before set_brk() (and revert the brk randomization), it works,
including columns.

If I add

+//     elf_bss += random;

before set_brk(), I break everything.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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