Subject: Re: [PATCH v7 0/4] KASAN for arm64
To: Andrey Ryabinin <ryabinin.a.a@gmail.com>
References: <1444665180-301-1-git-send-email-ryabinin.a.a@gmail.com>
 <20151013083432.GG6320@e104818-lin.cambridge.arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        linux-arm-kernel@lists.infradead.org, Yury <yury.norov@gmail.com>,
        Alexey Klimov <klimov.linux@gmail.com>, Arnd Bergmann <arnd@arndb.de>,
        linux-mm@kvack.org, Andrey Konovalov <andreyknvl@google.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-kernel@vger.kernel.org, kasan-dev <kasan-dev@googlegroups.com>,
        David Keitel <dkeitel@codeaurora.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>
From: "Suzuki K. Poulose" <Suzuki.Poulose@arm.com>
Message-ID: <5649BAFD.6030005@arm.com>
Date: Mon, 16 Nov 2015 11:16:13 +0000
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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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