linux-kernel - Re: [PATCH 1/2] x86: fix norandmaps

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Message-ID: <2a3a4365-b3e1-5d52-0f4c-d7bdfaff627f@virtuozzo.com>
Date:   Mon, 10 Jul 2017 14:56:00 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86: fix norandmaps

On 07/10/2017 02:14 PM, Oleg Nesterov wrote:
> Documentation/admin-guide/kernel-parameters.txt says:
> 
>      norandmaps  Don't use address space randomization. Equivalent
>                  to echo 0 > /proc/sys/kernel/randomize_va_space
> 
> but it doesn't work because arch_rnd() which is used to randomize
> mm->mmap_base returns a random value unconditionally.
> 
> Shift the PF_RANDOMIZE check from arch_mmap_rnd() to arch_rnd().
> 
> Fixes: 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()")
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Thanks, Oleg,
Reviewed-by: Dmitry Safonov <dsafonov@...tuozzo.com>

> ---
>   arch/x86/mm/mmap.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 19ad095..6369d04 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -82,13 +82,13 @@ static int mmap_is_legacy(void)
>   
>   static unsigned long arch_rnd(unsigned int rndbits)
>   {
> +	if (!(current->flags & PF_RANDOMIZE))
> +		return 0;
>   	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
>   }
>   
>   unsigned long arch_mmap_rnd(void)
>   {
> -	if (!(current->flags & PF_RANDOMIZE))
> -		return 0;
>   	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
>   }
>   
> 


-- 
              Dmitry