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Date: Tue, 25 Jul 2006 03:46:39 -0400
From: Chuck Ebbert <76306.1226@compuserve.com>
Subject: [PATCH for 2.6.18rc2] [1/7] i386/x86-64: Don't randomize
  stack top when...
To: Andi Kleen <ak@suse.de>
Cc: Linus Torvalds <torvalds@osdl.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>, Arjan van de Ven <arjan@infradead.org>
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In-Reply-To: <44c514a8.6HlRR82y133O2bd0%ak@suse.de>

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:

        unsigned int r = get_random_int();
        sp &= ~0x7f;
        sp -= 128 * ((r % 32) + (r / 32 % 16));
        return sp;

-- 
Chuck