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Subject: Re: [PATCH v3 03/11] arm64: Consider stack randomization for mmap
 base only when necessary
To:     Kees Cook <keescook@chromium.org>
Cc:     Andrew Morton <akpm@linux-foundation.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>,
        Luis Chamberlain <mcgrof@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        linux-mips@vger.kernel.org, linux-riscv@lists.infradead.org,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
References: <20190417052247.17809-1-alex@ghiti.fr>
 <20190417052247.17809-4-alex@ghiti.fr>
 <CAGXu5jKo26zXw=jfKSzr_pnfx5Zux+fVbY7V9bJwEMApDcFi8w@mail.gmail.com>
From:   Alex Ghiti <alex@ghiti.fr>
Message-ID: <b2d80348-a3d4-ffcc-d174-0a7a244dae0b@ghiti.fr>
Date:   Thu, 18 Apr 2019 01:24:32 -0400
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On 4/18/19 12:37 AM, Kees Cook wrote:
> On Wed, Apr 17, 2019 at 12:26 AM Alexandre Ghiti <alex@ghiti.fr> wrote:
>> Do not offset mmap base address because of stack randomization if
>> current task does not want randomization.
> Maybe mention that this makes this logic match the existing x86 behavior too?


Ok I will add this in case of a v4.


>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> Acked-by: Kees Cook <keescook@chromium.org>

Thanks !


>
> -Kees
>
>> ---
>>   arch/arm64/mm/mmap.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
>> index ed4f9915f2b8..ac89686c4af8 100644
>> --- a/arch/arm64/mm/mmap.c
>> +++ b/arch/arm64/mm/mmap.c
>> @@ -65,7 +65,11 @@ unsigned long arch_mmap_rnd(void)
>>   static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>>   {
>>          unsigned long gap = rlim_stack->rlim_cur;
>> -       unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
>> +       unsigned long pad = stack_guard_gap;
>> +
>> +       /* Account for stack randomization if necessary */
>> +       if (current->flags & PF_RANDOMIZE)
>> +               pad += (STACK_RND_MASK << PAGE_SHIFT);
>>
>>          /* Values close to RLIM_INFINITY can overflow. */
>>          if (gap + pad > gap)
>> --
>> 2.20.1
>>
>