Re: [PATCH] [RFC] ubsan: disallow bounds checking with gcov on broken gcc

From: Kees Cook <keescook@chromium.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Arnd Bergmann <arnd@kernel.org>,
	kasan-dev@googlegroups.com,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Marco Elver <elver@google.com>,
	linux-media@vger.kernel.org, linux-crypto@vger.kernel.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Ard Biesheuvel <ardb@kernel.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Dan Carpenter <dan.carpenter@linaro.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Tom Rix <trix@redhat.com>, Josh Poimboeuf <jpoimboe@kernel.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org, llvm@lists.linux.dev
Subject: Re: [PATCH] [RFC] ubsan: disallow bounds checking with gcov on broken gcc
Date: Thu, 1 Jun 2023 11:28:11 -0700	[thread overview]
Message-ID: <202306011127.B801968@keescook> (raw)
In-Reply-To: <f6fcae8a-9b50-48e4-84e9-c37613226c63@app.fastmail.com>

On Thu, Jun 01, 2023 at 07:50:38PM +0200, Arnd Bergmann wrote:
> On Thu, Jun 1, 2023, at 18:14, Kees Cook wrote:
> > On Thu, Jun 01, 2023 at 05:18:11PM +0200, Arnd Bergmann wrote:
> >
> > I think more production systems will have CONFIG_UBSAN_BOUNDS enabled
> > (e.g. Ubuntu has had it enabled for more than a year now) than GCOV,
> > so I'd prefer we maintain all*config coverage for the more commonly
> > used config.
> 
> Fair enough, I can send that as v2, but let's see what the others
> think first.
> 
> >>  config CC_HAS_UBSAN_BOUNDS_STRICT
> >>  	def_bool $(cc-option,-fsanitize=bounds-strict)
> >> +	# work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110074
> >> +	depends on GCC_VERSION > 140000 || !GCOV_PROFILE_ALL
> >>  	help
> >>  	  The -fsanitize=bounds-strict option is only available on GCC,
> >>  	  but uses the more strict handling of arrays that includes knowledge
> >
> > Alternatively, how about falling back to -fsanitize=bounds instead, as
> > that (which has less coverage) wasn't triggering the stack frame
> > warnings?
> >
> > i.e. fall back through these:
> > 	-fsanitize=array-bounds (Clang)
> > 	-fsanitize=bounds-strict (!GCOV || bug fixed in GCC)
> > 	-fsanitize=bounds
> 
> From what I can tell, -fsanitize=bounds has the same problem
> as -fsanitize=bounds-strict, so that would not help.

Ah, did something change with GCOV? This (bounds vs bounds-strict) is
the only recent change to CONFIG_UBSAN_BOUNDS...

-- 
Kees Cook