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From: Andrey Konovalov <andreyknvl@google.com>
Date: Fri, 9 Mar 2018 19:06:59 +0100
Message-ID: <CAAeHK+y+sAGYSsfUHk4De2QiAPEN_+_ACxCoQ7XMSkvpseoFVQ@mail.gmail.com>
Subject: Re: [RFC PATCH 14/14] khwasan: default the instrumentation mode to inline
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To: Mark Rutland <mark.rutland@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, Jonathan Corbet <corbet@lwn.net>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.com>, Christopher Li <sparse@chrisli.org>, Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, Masahiro Yamada <yamada.masahiro@socionext.com>, Michal Marek <michal.lkml@markovi.net>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Yury Norov <ynorov@caviumnetworks.com>, Nick Desaulniers <ndesaulniers@google.com>, Marc Zyngier <marc.zyngier@arm.com>, Bob Picco <bob.picco@oracle.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Kristina Martsenko <kristina.martsenko@arm.com>, Punit Agrawal <punit.agrawal@arm.com>, Dave Martin <Dave.Martin@arm.com>, James Morse <james.morse@arm.com>, Julien Thierry <julien.thierry@arm.com>, Michael Weiser <michael.weiser@gmx.de>, Steve Capper <steve.capper@arm.com>, Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Sandipan Das <sandipan@linux.vnet.ibm.com>, Paul Lawrence <paullawrence@google.com>, David Woodhouse <dwmw@amazon.co.uk>, Kees Cook <keescook@chromium.org>, Geert Uytterhoeven <geert@linux-m68k.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Arnd Bergmann <arnd@arndb.de>, kasan-dev <kasan-dev@googlegroups.com>, linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-ext4@vger.kernel.org, linux-sparse@vger.kernel.org, Linux Memory Management List <linux-mm@kvack.org>, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, Kostya Serebryany <kcc@google.com>, Evgeniy Stepanov <eugenis@google.com>, Lee Smith <Lee.Smith@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Kees Cook <keescook@google.com>, Jann Horn <jannh@google.com>, Mark Brand <markbrand@google.com>

On Mon, Mar 5, 2018 at 3:54 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Fri, Mar 02, 2018 at 08:44:33PM +0100, Andrey Konovalov wrote:
>> There are two reasons to use outline instrumentation:
>> 1. Outline instrumentation reduces the size of the kernel text, and should
>>    be used where this size matters.
>> 2. Outline instrumentation is less invasive and can be used for debugging
>>    for KASAN developers, when it's not clear whether some issue is caused
>>    by KASAN or by something else.
>>
>> For the rest cases inline instrumentation is preferrable, since it's
>> faster.
>>
>> This patch changes the default instrumentation mode to inline.
>> ---
>>  lib/Kconfig.kasan | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
>> index ab34e7d7d3a7..8ea6ae26b4a3 100644
>> --- a/lib/Kconfig.kasan
>> +++ b/lib/Kconfig.kasan
>> @@ -70,7 +70,7 @@ config KASAN_EXTRA
>>  choice
>>       prompt "Instrumentation type"
>>       depends on KASAN
>> -     default KASAN_OUTLINE
>> +     default KASAN_INLINE
>
> Some compilers don't support KASAN_INLINE, but do support KASAN_OUTLINE.
> IIRC that includes the latest clang release, but I could be wrong.
>
> If that's the case, changing the default here does not seem ideal.
>

Hi Mark!

GCC before 5.0 doesn't support KASAN_INLINE, but AFAIU will fallback
to outline instrumentation in this case.

Latest Clang Release doesn't support KASAN_INLINE (although current
trunk does) and falls back to outline instrumentation.

So nothing should break, but people with newer compilers should get
the benefits of using the inline instrumentation by default.

Thanks!