Re: [PATCH] arm64: kasan: instrument user memory access API

From: Shi, Yang
Date: Fri May 27 2016 - 12:34:12 EST

On 5/27/2016 4:02 AM, Andrey Ryabinin wrote:

On 05/26/2016 09:43 PM, Yang Shi wrote:
The upstream commit 1771c6e1a567ea0ba2cccc0a4ffe68a1419fd8ef
("x86/kasan: instrument user memory access API") added KASAN instrument to
x86 user memory access API, so added such instrument to ARM64 too.

Tested by test_kasan module.

Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxx>
arch/arm64/include/asm/uaccess.h | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

Please, cover __copy_from_user() and __copy_to_user() too.
Unlike x86, your patch doesn't instrument these two.

I should elaborated this in my review. Yes, I did think about it, but unlike x86, __copy_to/from_user are implemented by asm code on ARM64. If I add kasan_check_read/write into them, I have to move the registers around to prepare the parameters for kasan calls, then restore them after the call, for example the below code for __copy_to_user:

mov x9, x0
mov x10, x1
mov x11, x2
mov x0, x10
mov x1, x11
bl kasan_check_read
mov x0, x9
mov x1, x10

So, I'm wondering if it is worth or not since __copy_to/from_user are just called at a couple of places, i.e. sctp, a couple of drivers, etc and not used too much. Actually, I think some of them could be replaced by __copy_to/from_user_inatomic.

Any idea is appreciated.