Re: [PATCH for 2.6.18rc2] [1/7] i386/x86-64: Don't randomize stacktop when...

[Arjan van de Ven]

On Tue, 2006-07-25 at 03:46 -0400, Chuck Ebbert wrote:
> In-Reply-To: <44c514a8.6HlRR82y133O2bd0%ak@xxxxxxx>
> 
> On Mon, 24 Jul 2006 20:42:48 +0200, Andi Kleen wrote:
> > 
> > --- linux.orig/arch/i386/kernel/process.c
> > +++ linux/arch/i386/kernel/process.c
> > @@ -37,6 +37,7 @@
> >  #include <linux/kallsyms.h>
> >  #include <linux/ptrace.h>
> >  #include <linux/random.h>
> > +#include <linux/personality.h>
> >  
> >  #include <asm/uaccess.h>
> >  #include <asm/pgtable.h>
> > @@ -905,7 +906,7 @@ asmlinkage int sys_get_thread_area(struc
> >  
> >  unsigned long arch_align_stack(unsigned long sp)
> >  {
> > -     if (randomize_va_space)
> > +     if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
> >               sp -= get_random_int() % 8192;
> >       return sp & ~0xf;
> >  }
> 
> I think this needs to be done always, at least on P4.  It really isn't
> 'randomization' at the same high level as the rest -- more like a small
> adjustment.  And the offset should be a multiple of 128 and < 7K (not
> 8K.) Something like this:

the 8K was what Intel proposed for 2.4 quite a while ago and has been in
use in linux for years and years... Can you explain why you are saying
7Kb? throwing away that 1Kb of cache associativity is unfortunate and
shouldn't be done unless there's a good reason, so I'm quite interested
in finding out your reason ;)

Greetings,
   Arjan van de Ven

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