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

Andrey Ryabinin
2017-03-03T13:52:41Z

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@arndb.de>
> ---
> 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.

> +#else
> +#define noinline_for_kasan inline
> +#endif
> +
> #ifndef __always_inline
> #define __always_inline inline
> #endif
>