linux-kernel - Re: [PATCH v6 11/14] mips: Adjust brk randomization offset to fit generic version

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Date:   Fri, 9 Aug 2019 11:45:51 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
        Catalin Marinas <catalin.marinas@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Luis Chamberlain <mcgrof@...nel.org>,
        Paul Burton <paul.burton@...s.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        James Hogan <jhogan@...nel.org>,
        linux-riscv@...ts.infradead.org, linux-mips@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        linux-arm-kernel@...ts.infradead.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v6 11/14] mips: Adjust brk randomization offset to fit
 generic version

On 8/8/19 11:19 AM, Sergei Shtylyov wrote:
> 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@...omium.org>
>> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
>> Acked-by: Paul Burton <paul.burton@...s.com>
>> Reviewed-by: Kees Cook <keescook@...omium.org>
>> Reviewed-by: Luis Chamberlain <mcgrof@...nel.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?

You're right, I could have. Again, this code gets removed afterwards, so 
I think it's ok
to leave it as is.

Anyway, thanks for your remarks Sergei !

Alex

>
> [...]
>
> MBR, Sergei
>
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