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SubjectRe: [PATCH v3 11/11] riscv: Make mmap allocation top-down by default
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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
>>
>

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