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References: <4ad725cc903f8534f8c8a60f0daade5e3d674f8d.1523554166.git.andreyknvl@google.com>
 <b849e2ff-3693-9546-5850-1ddcea23ee29@virtuozzo.com>
From: Andrey Konovalov <andreyknvl@google.com>
Date: Fri, 13 Apr 2018 19:34:47 +0200
Message-ID: <CAAeHK+y18zU_PAS5KB82PNqtvGNex+S0Jk3bWaE19=YjThaNow@mail.gmail.com>
Subject: Re: [PATCH] kasan: add no_sanitize attribute for clang builds
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Sender: owner-linux-mm@kvack.org
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To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, Andrew Morton <akpm@linux-foundation.org>, David Rientjes <rientjes@google.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, David Woodhouse <dwmw@amazon.co.uk>, Will Deacon <will.deacon@arm.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Paul Lawrence <paullawrence@google.com>, Sandipan Das <sandipan@linux.vnet.ibm.com>, Kees Cook <keescook@chromium.org>, LKML <linux-kernel@vger.kernel.org>, kasan-dev <kasan-dev@googlegroups.com>, Linux Memory Management List <linux-mm@kvack.org>, Kostya Serebryany <kcc@google.com>

On Fri, Apr 13, 2018 at 5:31 PM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
>
>
> On 04/12/2018 08:29 PM, Andrey Konovalov wrote:
>> KASAN uses the __no_sanitize_address macro to disable instrumentation
>> of particular functions. Right now it's defined only for GCC build,
>> which causes false positives when clang is used.
>>
>> This patch adds a definition for clang.
>>
>> Note, that clang's revision 329612 or higher is required.
>>
>> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>> ---
>>  include/linux/compiler-clang.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
>> index ceb96ecab96e..5a1d8580febe 100644
>> --- a/include/linux/compiler-clang.h
>> +++ b/include/linux/compiler-clang.h
>> @@ -25,6 +25,11 @@
>>  #define __SANITIZE_ADDRESS__
>>  #endif
>>
>> +#ifdef CONFIG_KASAN
>
> If, for whatever reason, developer decides to add __no_sanitize_address to some
> generic function, guess what will happen next when he/she will try to build CONFIG_KASAN=n kernel?

It's defined to nothing in compiler-gcc.h and redefined in
compiler-clang.h only if CONFIG_KASAN is enabled, so everything should
be fine. Am I missing something?

>
>> +#undef __no_sanitize_address
>> +#define __no_sanitize_address __attribute__((no_sanitize("address")))
>> +#endif
>> +
>>  /* Clang doesn't have a way to turn it off per-function, yet. */
>>  #ifdef __noretpoline
>>  #undef __noretpoline
>>