linux-kernel - Re: [PATCH v7 0/4] KASAN for arm64

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Date:	Mon, 16 Nov 2015 11:16:13 +0000
From:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
To:	Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, Yury <yury.norov@...il.com>,
	Alexey Klimov <klimov.linux@...il.com>,
	Arnd Bergmann <arnd@...db.de>, linux-mm@...ck.org,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	linux-kernel@...r.kernel.org,
	kasan-dev <kasan-dev@...glegroups.com>,
	David Keitel <dkeitel@...eaurora.org>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v7 0/4] KASAN for arm64

On 13/10/15 09:34, Catalin Marinas wrote:
> On Mon, Oct 12, 2015 at 06:52:56PM +0300, Andrey Ryabinin wrote:
>> Andrey Ryabinin (3):
>>    arm64: move PGD_SIZE definition to pgalloc.h
>>    arm64: add KASAN support
>>    Documentation/features/KASAN: arm64 supports KASAN now
>>
>> Linus Walleij (1):
>>    ARM64: kasan: print memory assignment
>
> Patches queued for 4.4. Thanks.
>

Hi,

I get the following failure with KASAN + 16K_PAGES + 48BIT_VA, with 4.4-rc1:


arch/arm64/mm/kasan_init.c: In function ‘kasan_early_init’:
include/linux/compiler.h:484:38: error: call to ‘__compiletime_assert_95’ declared with attribute error: BUILD_BUG_ON failed: !IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE)
   _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                       ^
include/linux/compiler.h:467:4: note: in definition of macro ‘__compiletime_assert’
     prefix ## suffix();    \
     ^
include/linux/compiler.h:484:2: note: in expansion of macro ‘_compiletime_assert’
   _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
   ^
include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
  #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                      ^
include/linux/bug.h:74:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
   BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
   ^
arch/arm64/mm/kasan_init.c:95:2: note: in expansion of macro ‘BUILD_BUG_ON’
   BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));


---

The problem is that the PGDIR_SIZE is (1UL << 47) with 16K+48bit, which makes
the KASAN_SHADOW_END unaligned(which is aligned to (1UL << (48 - 3)) ). Is the
alignment really needed ? Thoughts on how best we could fix this ?

Cheers
Suzuki

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