linux-kernel - Re: [PATCHv4 1/5] x86/mm: split arch_mmap

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Date:   Fri, 10 Feb 2017 21:25:06 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dmitry Safonov <dsafonov@...tuozzo.com>,
        linux-kernel@...r.kernel.org, 0x7f454c46@...il.com,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        linux-mm@...ck.org
Subject: Re: [PATCHv4 1/5] x86/mm: split arch_mmap_rnd() on compat/native
 versions

On Fri, Feb 10, 2017 at 09:10:30PM +0100, Thomas Gleixner wrote:
> On Thu, 9 Feb 2017, Borislav Petkov wrote:
> > I can't say that I'm thrilled about the ifdeffery this is adding.
> > 
> > But I can't think of a cleaner approach at a quick glance, though -
> > that's generic and arch-specific code intertwined muck. Sad face.
> 
> It's trivial enough to do ....
> 
> Thanks,
> 
> 	tglx
> 
> ---
>  arch/x86/mm/mmap.c |   22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -55,6 +55,10 @@ static unsigned long stack_maxrandom_siz
>  #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
>  #define MAX_GAP (TASK_SIZE/6*5)
>  
> +#ifndef CONFIG_COMPAT
> +# define mmap_rnd_compat_bits	mmap_rnd_bits
> +#endif
> +
>  static int mmap_is_legacy(void)
>  {
>  	if (current->personality & ADDR_COMPAT_LAYOUT)
> @@ -66,20 +70,14 @@ static int mmap_is_legacy(void)
>  	return sysctl_legacy_va_layout;
>  }
>  
> -unsigned long arch_mmap_rnd(void)
> +static unsigned long arch_rnd(unsigned int rndbits)
>  {
> -	unsigned long rnd;
> -
> -	if (mmap_is_ia32())
> -#ifdef CONFIG_COMPAT
> -		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
> -#else
> -		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
> -#endif
> -	else
> -		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
> +	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
> +}
>  
> -	return rnd << PAGE_SHIFT;
> +unsigned long arch_mmap_rnd(void)
> +{
> +	return arch_rnd(mmap_is_ia32() ? mmap_rnd_compat_bits : mmap_rnd_bits);
>  }

Ha! Nice. :-)

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--