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

-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
>


--
Kees Cook

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