linux-kernel - Re: [PATCH for 2.6.18-rc2] [2/8] i386/x86-64: Don't randomize stack top when no randomization personality

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Message-Id: <200607171424.49827.a1426z@gawab.com>
Date:	Mon, 17 Jul 2006 14:24:49 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH for 2.6.18-rc2] [2/8] i386/x86-64: Don't randomize stack top when no randomization personality

Ingo Molnar wrote:
> * Andi Kleen <ak@...e.de> wrote:
> >  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'm not opposing this patch at all, but didnt the performance problems
> go away when the 0xf was changed to 0x7f?

Yes, 0x7f is critical, but I'm not sure about side-effects.

> looks good otherwise.

except this one

> --- linux.orig/fs/binfmt_elf.c
> +++ linux/fs/binfmt_elf.c
> @@ -515,7 +515,8 @@ static unsigned long randomize_stack_top
>  {
>         unsigned int random_variable = 0;
>
> -       if (current->flags & PF_RANDOMIZE) {
> +       if ((current->flags & PF_RANDOMIZE) &&
> +               !(current->personality & ADDR_NO_RANDOMIZE)) {
>                 random_variable = get_random_int() & STACK_RND_MASK;
>                 random_variable <<= PAGE_SHIFT;
>         }

Why are you testing twice?

Thanks!

--
Al

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