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Date:   Wed, 18 Oct 2023 12:42:53 -0400
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Subject: Re: [PATCH] lib: Kconfig: disable dynamic sanitizers for test builds
Content-Language: en-US
To:     Marco Elver <elver@google.com>
Cc:     linux-kernel@vger.kernel.org,
        Rodrigo Siqueira <rodrigo.siqueira@amd.com>,
        Harry Wentland <harry.wentland@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, kasan-dev@googlegroups.com,
        llvm@lists.linux.dev, Arnd Bergmann <arnd@arndb.de>
References: <20231018153147.167393-1-hamza.mahfooz@amd.com>
 <CANpmjNPZ0Eii3ZTrVqEL2Ez0Jv23y-emLBCLSZ==xmH--4E65g@mail.gmail.com>
From:   Hamza Mahfooz <hamza.mahfooz@amd.com>
In-Reply-To: <CANpmjNPZ0Eii3ZTrVqEL2Ez0Jv23y-emLBCLSZ==xmH--4E65g@mail.gmail.com>
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On 10/18/23 12:22, Marco Elver wrote:
> On Wed, 18 Oct 2023 at 17:32, 'Hamza Mahfooz' via kasan-dev
> <kasan-dev@googlegroups.com> wrote:
>>
>> kasan, kcsan and kmsan all have the tendency to blow up the stack
>> and there isn't a lot of value in having them enabled for test builds,
>> since they are intended to be useful for runtime debugging. So, disable
>> them for test builds.
>>
>> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
>> ---
>>   lib/Kconfig.kasan | 1 +
>>   lib/Kconfig.kcsan | 1 +
>>   lib/Kconfig.kmsan | 1 +
>>   3 files changed, 3 insertions(+)
> 
> Do you have links to discussions that motivate this change? This has
> been discussed in the past. One recommendation is to adjust the

Sure, you can checkout:
https://lore.kernel.org/amd-gfx/CADnq5_OyO9CHqahFvdnx7-8s9654udgdfhUntyxfjae+iHey0Q@mail.gmail.com/T/#m5d227dc1ef07b1f4953312287dce4568666c5e09

> build/test scripts to exclude some combination of configs if they are
> causing issues. Or we increase CONFIG_FRAME_WARN if one of them is
> enabled (KMSAN sets it to 0, 32-bit KASAN increases it a bit).
> 
> That being said, we're aware of KASAN having had more issues and there
> are some suboptions that have been disabled because of that (like
> KASAN_STACK). I'm not sure if Clang's KASAN instrumentation has had
> some recent improvements (we did investigate it, but I can't recall
> what the outcome was [1]) - maybe try a more recent compiler? However,
> KCSAN and KMSAN shouldn't have any issues (if KMSAN is enabled,

This patch was initially motivated by KCSAN (i.e. I am able to get it to
blow up the stack with a minimal .config). I don't mind dropping the
other ones since I only included them because Nathan implied that they
could cause similar issues.

> FRAME_WARN is 0). And having build tests with them enabled isn't
> useless at all: we're making sure that these tools (even though only
> for debugging), still work. We _want_ them to work during random build
> testing!
> 
> Please share the concrete problem you're having, because this change
> will make things worse for everyone in the long run.
> 
> [1] https://github.com/llvm/llvm-project/issues/38157
> 
>> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
>> index fdca89c05745..fbd85c4872c0 100644
>> --- a/lib/Kconfig.kasan
>> +++ b/lib/Kconfig.kasan
>> @@ -38,6 +38,7 @@ menuconfig KASAN
>>                      CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
>>                     HAVE_ARCH_KASAN_HW_TAGS
>>          depends on (SLUB && SYSFS && !SLUB_TINY) || (SLAB && !DEBUG_SLAB)
>> +       depends on !COMPILE_TEST
>>          select STACKDEPOT_ALWAYS_INIT
>>          help
>>            Enables KASAN (Kernel Address Sanitizer) - a dynamic memory safety
> 
> This also disables KASAN_HW_TAGS, which is actually enabled in
> production kernels and does not use any compiler instrumentation.
> 
>> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
>> index 609ddfc73de5..7bcefdbfb46f 100644
>> --- a/lib/Kconfig.kcsan
>> +++ b/lib/Kconfig.kcsan
>> @@ -14,6 +14,7 @@ menuconfig KCSAN
>>          bool "KCSAN: dynamic data race detector"
>>          depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
>>          depends on DEBUG_KERNEL && !KASAN
>> +       depends on !COMPILE_TEST
>>          select CONSTRUCTORS
>>          select STACKTRACE
>>          help
>> diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
>> index ef2c8f256c57..eb05c885d3fd 100644
>> --- a/lib/Kconfig.kmsan
>> +++ b/lib/Kconfig.kmsan
>> @@ -13,6 +13,7 @@ config KMSAN
>>          depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
>>          depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
>>          depends on !PREEMPT_RT
>> +       depends on !COMPILE_TEST
> 
> KMSAN already selects FRAME_WARN of 0 and should not cause you any
> issues during build testing.
> 
> Nack.
-- 
Hamza