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Subject: Re: [PATCH v3 11/11] riscv: Make mmap allocation top-down by default
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>
 <20190417052247.17809-12-alex@ghiti.fr>
 <CAGXu5jJcQzDQGy907H0WXu-q1sPQaXgjuFbHHW60ajUuksZb3A@mail.gmail.com>
From:   Alex Ghiti <alex@ghiti.fr>
Message-ID: <23d2a38d-363a-929c-5296-c2f8c3b7d1b4@ghiti.fr>
Date:   Thu, 18 Apr 2019 02:09:08 -0400
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On 4/18/19 1:31 AM, Kees Cook wrote:
> On Wed, Apr 17, 2019 at 12:34 AM Alexandre Ghiti <alex@ghiti.fr> wrote:
>> In order to avoid wasting user address space by using bottom-up mmap
>> allocation scheme, prefer top-down scheme when possible.
>>
>> Before:
>> root@qemuriscv64:~# cat /proc/self/maps
>> 00010000-00016000 r-xp 00000000 fe:00 6389       /bin/cat.coreutils
>> 00016000-00017000 r--p 00005000 fe:00 6389       /bin/cat.coreutils
>> 00017000-00018000 rw-p 00006000 fe:00 6389       /bin/cat.coreutils
>> 00018000-00039000 rw-p 00000000 00:00 0          [heap]
>> 1555556000-155556d000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
>> 155556d000-155556e000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
>> 155556e000-155556f000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
>> 155556f000-1555570000 rw-p 00000000 00:00 0
>> 1555570000-1555572000 r-xp 00000000 00:00 0      [vdso]
>> 1555574000-1555576000 rw-p 00000000 00:00 0
>> 1555576000-1555674000 r-xp 00000000 fe:00 7187   /lib/libc-2.28.so
>> 1555674000-1555678000 r--p 000fd000 fe:00 7187   /lib/libc-2.28.so
>> 1555678000-155567a000 rw-p 00101000 fe:00 7187   /lib/libc-2.28.so
>> 155567a000-15556a0000 rw-p 00000000 00:00 0
>> 3fffb90000-3fffbb1000 rw-p 00000000 00:00 0      [stack]
>>
>> After:
>> root@qemuriscv64:~# cat /proc/self/maps
>> 00010000-00016000 r-xp 00000000 fe:00 6389       /bin/cat.coreutils
>> 00016000-00017000 r--p 00005000 fe:00 6389       /bin/cat.coreutils
>> 00017000-00018000 rw-p 00006000 fe:00 6389       /bin/cat.coreutils
>> 00018000-00039000 rw-p 00000000 00:00 0          [heap]
>> 3ff7eb6000-3ff7ed8000 rw-p 00000000 00:00 0
>> 3ff7ed8000-3ff7fd6000 r-xp 00000000 fe:00 7187   /lib/libc-2.28.so
>> 3ff7fd6000-3ff7fda000 r--p 000fd000 fe:00 7187   /lib/libc-2.28.so
>> 3ff7fda000-3ff7fdc000 rw-p 00101000 fe:00 7187   /lib/libc-2.28.so
>> 3ff7fdc000-3ff7fe2000 rw-p 00000000 00:00 0
>> 3ff7fe4000-3ff7fe6000 r-xp 00000000 00:00 0      [vdso]
>> 3ff7fe6000-3ff7ffd000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
>> 3ff7ffd000-3ff7ffe000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
>> 3ff7ffe000-3ff7fff000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
>> 3ff7fff000-3ff8000000 rw-p 00000000 00:00 0
>> 3fff888000-3fff8a9000 rw-p 00000000 00:00 0      [stack]
>>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Kees Cook <keescook@chromium.org>


Thank you very much for all your comments,

Alex


>
> -Kees
>
>> ---
>>   arch/riscv/Kconfig | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index eb56c82d8aa1..f5897e0dbc1c 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -49,6 +49,17 @@ config RISCV
>>          select GENERIC_IRQ_MULTI_HANDLER
>>          select ARCH_HAS_PTE_SPECIAL
>>          select HAVE_EBPF_JIT if 64BIT
>> +       select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
>> +       select HAVE_ARCH_MMAP_RND_BITS
>> +
>> +config ARCH_MMAP_RND_BITS_MIN
>> +       default 18
>> +
>> +# max bits determined by the following formula:
>> +#  VA_BITS - PAGE_SHIFT - 3
>> +config ARCH_MMAP_RND_BITS_MAX
>> +       default 33 if 64BIT # SV48 based
>> +       default 18
>>
>>   config MMU
>>          def_bool y
>> --
>> 2.20.1
>>
>