linux-kernel - Re: [PATCH] kasan: Always respect CONFIG_KASAN

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Date:   Sun, 3 Oct 2021 20:04:53 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Marco Elver <elver@...gle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH] kasan: Always respect CONFIG_KASAN_STACK

On Wed, Sep 22, 2021 at 10:55 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Currently, the asan-stack parameter is only passed along if
> CFLAGS_KASAN_SHADOW is not empty, which requires KASAN_SHADOW_OFFSET to
> be defined in Kconfig so that the value can be checked. In RISC-V's
> case, KASAN_SHADOW_OFFSET is not defined in Kconfig, which means that
> asan-stack does not get disabled with clang even when CONFIG_KASAN_STACK
> is disabled, resulting in large stack warnings with allmodconfig:
>
> drivers/video/fbdev/omap2/omapfb/displays/panel-lgphilips-lb035q02.c:117:12:
> error: stack frame size (14400) exceeds limit (2048) in function
> 'lb035q02_connect' [-Werror,-Wframe-larger-than]
> static int lb035q02_connect(struct omap_dss_device *dssdev)
>            ^
> 1 error generated.
>
> Ensure that the value of CONFIG_KASAN_STACK is always passed along to
> the compiler so that these warnings do not happen when
> CONFIG_KASAN_STACK is disabled.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1453
> References: 6baec880d7a5 ("kasan: turn off asan-stack for clang-8 and earlier")
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  scripts/Makefile.kasan | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index 801c415bac59..b9e94c5e7097 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -33,10 +33,11 @@ else
>         CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
>          $(call cc-param,asan-globals=1) \
>          $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
> -        $(call cc-param,asan-stack=$(stack_enable)) \
>          $(call cc-param,asan-instrument-allocas=1)
>  endif

This part of code always looked weird to me.

Shouldn't we be able to pull all these options out of the else section?

Then, the code structure would make sense: first, try applying
KASAN_SHADOW_OFFSET; if failed, use CFLAGS_KASAN_MINIMAL; and then try
applying all these options one by one.

> +CFLAGS_KASAN += $(call cc-param,asan-stack=$(stack_enable))
> +
>  endif # CONFIG_KASAN_GENERIC
>
>  ifdef CONFIG_KASAN_SW_TAGS
>
> base-commit: 4057525736b159bd456732d11270af2cc49ec21f
> --
> 2.33.0.514.g99c99ed825
>