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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 14 Sep 2020 14:17:39 -0700
Message-ID: <CAKwvOdmMAc5zhLQMr-6WvrJJ4vbzwMpav36Y6V_DBBVjf4i72g@mail.gmail.com>
Subject: Re: [PATCH 06/14] Fix CFLAGS for UBSAN_BOUNDS on Clang
To:     George-Aurelian Popescu <georgepope@google.com>
Cc:     Marc Zyngier <maz@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        kvmarm@lists.cs.columbia.edu, LKML <linux-kernel@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
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+ kernel-dynamic-tools to help review.

On Mon, Sep 14, 2020 at 10:28 AM George-Aurelian Popescu
<georgepope@google.com> wrote:
>
> From: George Popescu <georgepope@google.com>
>
> When the kernel is compiled with Clang, UBSAN_BOUNDS inserts a brk after
> the handler call, preventing it from printing any information processed
> inside the buffer.
> For Clang -fsanitize=bounds expands to -fsanitize=array-bounds and
> -fsanitize=local-bounds, and the latter adds a brk after the handler
> call
>
> Signed-off-by: George Popescu <georgepope@google.com>
> ---
>  scripts/Makefile.ubsan | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> index 27348029b2b8..3d15ac346c97 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -4,7 +4,14 @@ ifdef CONFIG_UBSAN_ALIGNMENT
>  endif
>
>  ifdef CONFIG_UBSAN_BOUNDS
> -      CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
> +      # For Clang -fsanitize=bounds translates to -fsanitize=array-bounds and
> +      # -fsanitize=local-bounds; the latter adds a brk right after the
> +      # handler is called.
> +      ifdef CONFIG_CC_IS_CLANG
> +            CFLAGS_UBSAN += $(call cc-option, -fsanitize=array-bounds)

You can remove the cc-option check above; Clang has supported this
option for many releases.  (One less compiler invocation at build
time, FWIW).

You cannot remove the below cc-option; GCC only implemented that
sanitizer in the 5.0+ releases; the kernel still support GCC 4.9.

> +      else
> +            CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
> +      endif
>  endif
>
>  ifdef CONFIG_UBSAN_MISC
> --
> 2.28.0.618.gf4bc123cb7-goog
>


-- 
Thanks,
~Nick Desaulniers