linux-kernel - Re: [link@...gy.org: Re: [patch 2/8] personality: fix PER_CLEAR_ON

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Date:	Sun, 19 Jul 2009 21:55:19 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Athanasius <link@...gy.org>, Julien TINNES <jt@....org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...e.de>,
	Tavis Ormandy <taviso@....lonestar.org>,
	Christoph Hellwig <hch@...radead.org>,
	Kees Cook <kees@...ntu.com>, Eugene Teo <eugene@...hat.com>
Subject: Re: [link@...gy.org: Re: [patch 2/8] personality: fix PER_CLEAR_ON_SETID (CVE-2009-1895)]

Linus Torvalds <torvalds@...ux-foundation.org> writes:
>
> Other binaries are unhappy with address space randomization because they 
> need to get the absolute maximum contiguous VM space for some big array. 
> Ok, so that's less of an issue in 64-bit mode, but there really are 
> programs out there that link everything statically and want to run at a 
> low virtual address so that they can get 2.5GB of virtual memory for one 
> single big allocation. I've written crap like that myself. I'm not _proud_ 
> of it, but I could easily see that programs like that could be unhappy if 
> the system wiggles mmap's around for security issues.

Another common reason for not supporting randomized mappings is
when the program loads a "core file" that has pointers to data
on each boot, as a faster way to initialize data structures. 
That's common with LISP like languages for example, but even
e.g. gcc's pre compiled headers implementation works like this.

> Because compatibility is always of paramount importance.

If you want to give it a security angle: not supporting 
an old application anymore is a very severe DoS attack
for people using it.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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