Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 14 Sep 2020 15:13:14 -0700
From:   Kees Cook <keescook@chromium.org>
To:     George-Aurelian Popescu <georgepope@google.com>
Cc:     maz@kernel.org, catalin.marinas@arm.com, will@kernel.org,
        masahiroy@kernel.org, michal.lkml@markovi.net,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
        clang-built-linux@googlegroups.com, james.morse@arm.com,
        julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com,
        natechancellor@gmail.com, ndesaulniers@google.com,
        dbrazdil@google.com, broonie@kernel.org, maskray@google.com,
        ascull@google.com, akpm@linux-foundation.org, dvyukov@google.com,
        elver@google.com, tglx@linutronix.de, arnd@arndb.de
Subject: Re: [PATCH 06/14] Fix CFLAGS for UBSAN_BOUNDS on Clang
Message-ID: <202009141509.CDDC8C8@keescook>
References: <20200914172750.852684-1-georgepope@google.com>
 <20200914172750.852684-7-georgepope@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200914172750.852684-7-georgepope@google.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Sep 14, 2020 at 05:27:42PM +0000, George-Aurelian Popescu 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

That sounds like a compiler bug?

> 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)

This would mean losing the local-bounds coverage? Isn't that for locally
defined arrays on the stack?

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

-- 
Kees Cook