Re: [4.19 PATCH] MIPS: VDSO: Reduce VDSO_RANDOMIZE_SIZE to 64MB for 64bit

Sasha Levin
2018-11-07T03:23:27Z

On Mon, Nov 05, 2018 at 10:58:30PM +0000, Paul Burton wrote:
>From: Huacai Chen <chenhc@lemote.com>
>
>[ Upstream commit c61c7def1fa0a722610d89790e0255b74f3c07dd ]
>
>Commit ea7e0480a4b6 ("MIPS: VDSO: Always map near top of user memory")
>set VDSO_RANDOMIZE_SIZE to 256MB for 64bit kernel. But take a look at
>arch/mips/mm/mmap.c we can see that MIN_GAP is 128MB, which means the
>mmap_base may be at (user_address_top - 128MB). This make the stack be
>surrounded by mmaped areas, then stack expanding fails and causes a
>segmentation fault. Therefore, VDSO_RANDOMIZE_SIZE should be less than
>MIN_GAP and this patch reduce it to 64MB.
>
>Signed-off-by: Huacai Chen <chenhc@lemote.com>
>Signed-off-by: Paul Burton <paul.burton@mips.com>
>Fixes: ea7e0480a4b6 ("MIPS: VDSO: Always map near top of user memory")
>Patchwork: https://patchwork.linux-mips.org/patch/20910/
>Cc: Ralf Baechle <ralf@linux-mips.org>
>Cc: James Hogan <jhogan@kernel.org>
>Cc: linux-mips@linux-mips.org
>Cc: Fuxin Zhang <zhangfx@lemote.com>
>Cc: Zhangjin Wu <wuzhangjin@gmail.com>
>Cc: Huacai Chen <chenhuacai@gmail.com>
>Cc: stable@vger.kernel.org # 4.19

Now queued for 4.19, thank you.

--
Thanks,
Sasha