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

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Date:	Fri, 27 May 2016 09:34:03 -0700
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>, will.deacon@....com,
	catalin.marinas@....com
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mm@...ck.org, linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH] arm64: kasan: instrument user memory access API

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@...aro.org>
>> ---
>>  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.

Thanks,
Yang

>