Alright, trying again.  This patch is a bit smaller, easier to read,
more streamline.  randomize_stack_top() had code pulled out and put into
a static inline just before it; and the mmap() randomization
calculations are in fs/exec.c now. arch_align_stack() should also work
on stack-grows-up architectures like HPPA, not that it'll be used there
right now.


I am considering the following changes:

 - Base randomization on ranges, as suggested by Arjan van de Ven.  That
supersets current functionality, and we can implement entropy in bits
abstractly anyway (i.e. range = PAGE_SIZE * powr(2,ENTROPY_IN_BITS)).

 - Remove validation like 'if (random_bits > MAX_RANDOM_STACK_BITS)'.
These are not immediately useful; if SELinux hooks are added or such,
they would be, but they could also be added into the SELinux code for
those policy elements anyway.

 - Remove /*XXX: Put SELinux hooks here*/ comments.  This isn't hard to
figure out, anyone who wants to add SELinux hooks can figure this out then.

So before doing that, here's the current version.  Again, this has not
yet been compile tested, it's just scribbled out on paper.

Questions?  Comments?  Flames?  Pictures of your girlfriends?

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