linux-kernel - Re: [PATCH v4 11/14] mips: Adjust brk randomization offset to fit generic version

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Date:   Wed, 29 May 2019 13:12:10 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 11/14] mips: Adjust brk randomization offset to fit
 generic version

On Sun, May 26, 2019 at 09:47:43AM -0400, Alexandre Ghiti wrote:
> This commit simply bumps up to 32MB and 1GB the random offset
> of brk, compared to 8MB and 256MB, for 32bit and 64bit respectively.
> 
> Suggested-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  arch/mips/mm/mmap.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> index ffbe69f3a7d9..c052565b76fb 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
> @@ -16,6 +16,7 @@
>  #include <linux/random.h>
>  #include <linux/sched/signal.h>
>  #include <linux/sched/mm.h>
> +#include <linux/sizes.h>
>  
>  unsigned long shm_align_mask = PAGE_SIZE - 1;	/* Sane caches */
>  EXPORT_SYMBOL(shm_align_mask);
> @@ -189,11 +190,11 @@ static inline unsigned long brk_rnd(void)
>  	unsigned long rnd = get_random_long();
>  
>  	rnd = rnd << PAGE_SHIFT;
> -	/* 8MB for 32bit, 256MB for 64bit */
> +	/* 32MB for 32bit, 1GB for 64bit */
>  	if (TASK_IS_32BIT_ADDR)
> -		rnd = rnd & 0x7ffffful;
> +		rnd = rnd & SZ_32M;
>  	else
> -		rnd = rnd & 0xffffffful;
> +		rnd = rnd & SZ_1G;
>  
>  	return rnd;
>  }
> -- 
> 2.20.1
> 

-- 
Kees Cook