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Subject: Re: [PATCH v6 11/14] mips: Adjust brk randomization offset to fit
 generic version
To:     Alexandre Ghiti <alex@ghiti.fr>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>,
        James Hogan <jhogan@kernel.org>,
        Palmer Dabbelt <palmer@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mips@vger.kernel.org, linux-riscv@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
References: <20190808061756.19712-1-alex@ghiti.fr>
 <20190808061756.19712-12-alex@ghiti.fr>
From:   Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Message-ID: <68ec5cf6-6ba3-68ab-aa01-668b701c642f@cogentembedded.com>
Date:   Thu, 8 Aug 2019 12:19:56 +0300
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Hello!

On 08.08.2019 9:17, 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@chromium.org>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> Acked-by: Paul Burton <paul.burton@mips.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>   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 a7e84b2e71d7..ff6ab87e9c56 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
[...]
> @@ -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 - 1);
>   	else
> -		rnd = rnd & 0xffffffful;
> +		rnd = rnd & (SZ_1G - 1);

    Why not make these 'rnd &= SZ_* - 1', while at it anyways?

[...]

MBR, Sergei