Re: Patch 4/6 randomize the stack pointer

[Arjan van de Ven <arjan@infradead.org>]

On Thu, 2005-01-27 at 20:42 +0000, Christoph Hellwig wrote:
> On Thu, Jan 27, 2005 at 03:40:48PM -0500, Rik van Riel wrote:
> > On Thu, 27 Jan 2005, Christoph Hellwig wrote:
> > 
> > >>+unsigned long arch_align_stack(unsigned long sp)
> > >>+{
> > >>+	if (randomize_va_space)
> > >>+		sp -= ((get_random_int() % 4096) << 4);
> > >>+	return sp & ~0xf;
> > >>+}
> > >
> > >this looks like it'd work nicely on all architectures.
> > 
> > I guess it should work for all architectures using ELF,
> > not sure if it might break some of the more obscure
> > architectures ...
> 
> So it works for all CONFIG_MMU architectures.  Arjan mentioned that
> the minimum stack alignment might be different, so the 4 should
> become a per-arch constant and we can make the code unconditional
> for CONFIG_MMU?

and then there are architectures with an upward growing stack....
and maybe the alignment will even vary per cpu type (runtime) for some
architectures? Maybe arch maintainers can jump in quickly to say if a
scheme with a per arch shift factor would be sufficient or if all kinds
of horrors would creep up for them  (in which case a per arch function
would be more suitable)