linux-kernel - Re: [PATCH v6 0/6] KASAN for arm64

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Date:	Fri, 9 Oct 2015 13:18:09 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>, Yury <yury.norov@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Mark Salter <msalter@...hat.com>,
	Will Deacon <will.deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexey Klimov <klimov.linux@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	David Keitel <dkeitel@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v6 0/6] KASAN for arm64

2015-10-09 12:48 GMT+03:00 Mark Rutland <mark.rutland@....com>:
> On Fri, Oct 09, 2015 at 12:32:18PM +0300, Andrey Ryabinin wrote:
> [...]
>
>> I thought the EFI stub isolation patches create a copy of mem*() functions in the stub,
>> but they are just create aliases with __efistub_ prefix.
>>
>> We only need to create some more aliases for KASAN.
>> The following patch on top of the EFI stub isolation series works for me.
>>
>>
>> Signed-off-by: Andrey Ryabinin <ryabinin.a.a@...il.com>
>> ---
>>  arch/arm64/kernel/image.h | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
>> index e083af0..6eb8fee 100644
>> --- a/arch/arm64/kernel/image.h
>> +++ b/arch/arm64/kernel/image.h
>> @@ -80,6 +80,12 @@ __efistub_strcmp           = __pi_strcmp;
>>  __efistub_strncmp            = __pi_strncmp;
>>  __efistub___flush_dcache_area        = __pi___flush_dcache_area;
>>
>> +#ifdef CONFIG_KASAN
>> +__efistub___memcpy           = __pi_memcpy;
>> +__efistub___memmove          = __pi_memmove;
>> +__efistub___memset           = __pi_memset;
>> +#endif
>
> Ard's v4 stub isolation series has these aliases [1], as the stub
> requires these aliases regardless of KASAN in order to link.

Stub isolation series has __efistub_memcpy, not __efistub___memcpy
(two additional '_').
The thing is, KASAN provides own implementation of memcpy() which
checks memory before access.
The original 'memcpy()' becomes __memcpy(), so we could still use it.
In code that not instrumented by KASAN (like the EFI stub) we replace
KASAN's memcpy() with the original __mempcy():
#define memcpy() __memcpy()

So with CONFIG_KASAN=y the EFI stub uses __memcpy, thus we need to
create the __efistub___memcpy alias.

>
> Thanks,
> Mark.
>
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-October/375708.html
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