Unperformant Restrictions for non-x86_32 archs

[Kees Cook]

Hi Dieter,

I'm not sure I understand your request. The file you seem you mean is from
the Linux kernel package ("linux_3.2.0-17.27.diff.gz"), which collects all
the various patches Ubuntu carries for the kernel.

The routine you've quoted is from the NX-emulation patchset from:
http://git.kernel.org/?p=linux/kernel/git/kees/linux.git;a=shortlog;h=refs/heads/nx-emu
More specifically, this is a fix for brk area collisions when doing
ASCII-armored ASLR of the text segment for ELFs that have been built with
PIE.

Are you seeing some performance loss related to this?

And what did you want changed?

Thanks,

-Kees

On Wed, Feb 29, 2012 at 09:19:48AM +0000, Dieter Miosga wrote:
> Please change in file linux_32.0-17.27.diff
> at line 5268, and all following and preceding occurences , to
> 
> --- linux-3.2.0.orig/arch/x86/kernel/process.c
> +++ linux-3.2.0/arch/x86/kernel/process.c
> @@ -663,6 +663,16 @@
>  unsigned long arch_randomize_brk(struct mm_struct *mm)
>  {
>      unsigned long range_end = mm->brk + 0x02000000;
> -    return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
> +#ifdef CONFIG_X86_32
> +    unsigned long bump = 0;
> +    /* when using ASLR in arch_get_unmapped_exec_area, we must shove
> +       the brk segment way out of the way of the exec area, since it
> +       can collide with future allocations if not. */
> +    if ( (mm->get_unmapped_exec_area == arch_get_unmapped_exec_area) &&
> +         (mm->brk < 0x08000000) ) {
> +        bump = (TASK_SIZE/6);
> +    }
> +    return bump + (randomize_range(mm->brk, range_end, 0) ? : mm->brk);
> +#else
> +    return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
> +#endif
> 
>  }
> 
> 
> Sincerely,
> Dieter Miosga
> 
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-- 
Kees Cook