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Date: Wed, 7 Feb 2024 03:04:14 -0800
From: Kees Cook <keescook@chromium.org>
To: Justin Stitt <justinstitt@google.com>
Cc: Marco Elver <elver@google.com>, Miguel Ojeda <ojeda@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>, Hao Luo <haoluo@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nicolas Schier <nicolas@fjasle.eu>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Przemek Kitszel <przemyslaw.kitszel@intel.com>,
	linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
	linux-hardening@vger.kernel.org, linux-kbuild@vger.kernel.org
Subject: Re: [PATCH v3] ubsan: Reintroduce signed overflow sanitizer
Message-ID: <202402070255.36699AE147@keescook>
References: <20240205093725.make.582-kees@kernel.org>
 <20240207014528.5byuufi5f33bl6e2@google.com>
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On Wed, Feb 07, 2024 at 01:45:28AM +0000, Justin Stitt wrote:
> I wouldn't mind also seeing a test_ubsan_div_overflow test case here.
> 
> It has some quirky behavior and it'd be nice to test that the sanitizers
> properly capture it.
> 
> Check out this Godbolt: https://godbolt.org/z/qG5f1j6n1
> 
> tl;dr: with -fsanitize=signed-integer-overflow division (/) and
> remainder (%) operators still instrument arithmetic even with
> -fno-strict-overflow on.
> 
> This makes sense as division by 0 and INT_MIN/-1 are UBs that are not
> influenced by -fno-strict-overflow.

There is actually already a test_ubsan_divrem_overflow, but because the
failure modes result in a trap even without the sanitizer, it's disabled
in the test. For testing a crashing mode, it might be interesting to add
it to LKDTM, which is the crash tester...

> 
> Really though, the patch is fine and the above test case is optional and
> can be shipped later -- as such:
> 
> Reviewed-by: Justin Stitt <justinstitt@google.com>

Thanks!

-Kees

-- 
Kees Cook