linux-kernel - Re: [PATCH] Document randomize_va_space and CONFIG_COMPAT_BRK (was Re: [PATCH 2/2] ASLR: add possibility for more fine-grained tweaking)

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Message-ID: <Pine.LNX.4.64.0802071525520.30955@jikos.suse.cz>
Date:	Thu, 7 Feb 2008 15:30:11 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Hugh Dickins <hugh@...itas.com>, Pavel Machek <pavel@....cz>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Document randomize_va_space and CONFIG_COMPAT_BRK (was
 Re: [PATCH 2/2] ASLR: add possibility for more fine-grained	tweaking)

On Thu, 7 Feb 2008, Ingo Molnar wrote:

> i'm wondering about the following detail: i guess on 64-bit x86 kernels 
> we could default to !CONFIG_COMPAT_BRK? In 1997 there was no 64-bit x86. 
> Maybe for compat 32-bit binaries we could keep it off, but always do it 
> for 64-bit binaries.

So what do you think is proper behavior in situation when 
CONFIG_COMPAT_BRK=N on 64bit kernel, and 32bit-binary is loaded in 32bit 
emulation?

We can either leave the brk as-is, but that is in contradiction to user 
explictly specifying CONFIG_COMPAT_BRK=N. Is this what you propose?

Or we can randomize brk start in such situation, but that is the behavior 
we currently automatically have due to CONFIG_COMPAT_BRK=N, so no change 
is needed.

Thanks,

-- 
Jiri Kosina
SUSE Labs
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