Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation

[Alexander Potapenko]

On Fri, Mar 3, 2017 at 2:50 PM, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote:
>
>
> On 03/02/2017 07:38 PM, Arnd Bergmann wrote:
>> When CONFIG_KASAN is set, we can run into some code that uses incredible
>> amounts of kernel stack:
>>
>> drivers/staging/dgnc/dgnc_neo.c:1056:1: error: the frame size of 11112 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
>> drivers/media/i2c/cx25840/cx25840-core.c:4960:1: error: the frame size of 94000 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
>> drivers/media/dvb-frontends/stv090x.c:3430:1: error: the frame size of 5312 bytes is larger than 3072 bytes [-Werror=frame-larger-than=]
>>
>> This happens when a sanitizer uses stack memory each time an inline function
>> gets called. This introduces a new annotation for those functions to make
>> them either 'inline' or 'noinline' dependning on the CONFIG_KASAN symbol.
>>
>> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
>> ---
>>  include/linux/compiler.h | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
>> index f8110051188f..56b90897a459 100644
>> --- a/include/linux/compiler.h
>> +++ b/include/linux/compiler.h
>> @@ -416,6 +416,17 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
>>   */
>>  #define noinline_for_stack noinline
>>
>> +/*
>> + * CONFIG_KASAN can lead to extreme stack usage with certain patterns when
>> + * one function gets inlined many times and each instance requires a stack
>> + * ckeck.
>> + */
>> +#ifdef CONFIG_KASAN
>> +#define noinline_for_kasan noinline __maybe_unused
>
>
> noinline_iff_kasan might be a better name.  noinline_for_kasan gives the impression
> that we always noinline function for the sake of kasan, while noinline_iff_kasan
> clearly indicates that function is noinline only if kasan is used.
FWIW we may be facing the same problem with other compiler-based
tools, e.g. KMSAN (which isn't there yet).
So it might be better to choose a macro name that doesn't use the name "KASAN".
E.g. noinline_iff_memtool (or noinline_iff_memory_tool if that's not too long).
WDYT?
>> +#else
>> +#define noinline_for_kasan inline
>> +#endif
>> +
>>  #ifndef __always_inline
>>  #define __always_inline inline
>>  #endif
>>
>
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-- 
Alexander Potapenko
Software Engineer

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