Re: [PATCH] Break ELF_PLATFORM and stack pointer randomizationdependency

From: Ralf Baechle
Date: Fri Sep 28 2007 - 10:53:05 EST

On Fri, Sep 28, 2007 at 12:59:47PM +0200, Franck Bui-Huu wrote:

> Currently arch_align_stack() is used by fs/binfmt_elf.c to randomize
> stack pointer inside a page. But this happens only if ELF_PLATFORM
> symbol is defined.
> ELF_PLATFORM is normally set if the architecture wants to load
> implementation specific libraries for optimization. And currently a
> lot of architectures just yield this symbol to NULL.
> This is the case for MIPS architecture where ELF_PLATFORM is NULL but
> arch_align_stack() has been redefined to do stack inside page
> randomization. So in this case no randomization is actually done.
> This patch breaks this dependency which seems to be useless and allows
> platforms such MIPS to do the randomization.
> Signed-off-by: Franck Bui-Huu <fbuihuu@xxxxxxxxx>
> ---
> Andrew,
> I tried several times to poke people on the list to understand why
> this dependency exists at all, but unfortunately got no answers.
> So I'm submitting this patch to at least have some feedbacks. An
> easier solution would be to define ELF_PLATFORM to a dummy string
> for MIPS but it sounds very hackish.

Probably this was introduced a long time ago, so it's only recorded in
tglx's history git tree:

commit ccc875c1d2fe18b50020d501f1005ef46fc55fed
Author: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Date: Fri Mar 4 17:25:13 2005 -0800

[PATCH] Randomisation: stack randomisation

The patch below replaces the existing 8Kb randomisation of the userspace sta
pointer (which is currently only done for Hyperthreaded P-IVs) with a more
general randomisation over a 64Kb range. 64Kb is not a lot, but it's a star
and once the dust settles we can increase this value to a more agressive

Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>;a=commitdiff;h=ccc875c1d2fe18b50020d501f1005ef46fc55fed

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