netdev - Re: [PATCH 01/26] compiler: introduce noinline_for

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Date:   Fri, 3 Mar 2017 16:50:20 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Arnd Bergmann <arnd@...db.de>, <kasan-dev@...glegroups.com>
CC:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <linux-wireless@...r.kernel.org>,
        <kernel-build-reports@...ts.linaro.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation



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@...db.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
>