linux-kernel - Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization disabled

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Message-ID: <20111003150345.GP16720@zod.bos.redhat.com>
Date:	Mon, 3 Oct 2011 11:03:46 -0400
From:	Josh Boyer <jwboyer@...hat.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Andrew Morton <akpm00@...il.com>, Ingo Molnar <mingo@...e.hu>,
	hongjiu.lu@...el.com, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization
 disabled

On Mon, Oct 03, 2011 at 04:53:34PM +0200, Jiri Kosina wrote:
> On Thu, 29 Sep 2011, Josh Boyer wrote:
> 
> > Perhaps another check here for randomize?  Something like:
> > 
> > #if defined(CONFIG_X86) || defined(CONFIG_ARM)
> > 		if (current->flags & PF_RANDOMIZE)
> > 			load_bias = 0;
> > 		else if (vaddr)
> > 			load_bias = 0;
> > 		else
> > 			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE);
> > #else
> > 		load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> > #endif
> > 
> > If that's stupid, then feel free to tell me.  I won't pretend like I
> > understand what is going on here yet, but based on the explanation you
> > provided that might work.
> 
> I have just verified my hunch that the original patch from H.J. / Josh 
> breaks ASLR completely, so Andrew, please drop it for now.

Yes, please drop the original.

> I am now looking into how to fix things properly.
> 
> Josh, looking at what you are proposing -- do you see any reason to make 
> the behavior different in #else branch and in !(current->flags & 
> PF_RANDOMIZE) case?

I was mostly just trying to adapt H.J.'s patch to account for the
PF_RANDOMIZE case.  Looking at it a bit more, I'm not sure why they
would need to be different.  H.J., do you recall why you made that
change originally?

josh
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