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From:   Marco Elver <elver@google.com>
Date:   Thu, 23 Sep 2021 12:07:17 +0200
Message-ID: <CANpmjNNqgUSbiPHOpD8z5JAv2aiujxAMiO4siymYdU6zpid_2g@mail.gmail.com>
Subject: Re: [PATCH] kasan: Always respect CONFIG_KASAN_STACK
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Arnd Bergmann <arnd@arndb.de>, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        linux-riscv <linux-riscv@lists.infradead.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>
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On Wed, 22 Sept 2021 at 22:55, Nathan Chancellor <nathan@kernel.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@kernel.org>

Reviewed-by: Marco Elver <elver@google.com>

[ Which tree are you planning to take it through? ]

Note, arch/riscv/include/asm/kasan.h mentions KASAN_SHADOW_OFFSET in
comment (copied from arm64). Did RISC-V just forget to copy over the
Kconfig option?


> ---
>  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
>
> +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
>
>