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

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Message-ID: <202306011127.B801968@keescook>
Date:   Thu, 1 Jun 2023 11:28:11 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Arnd Bergmann <arnd@...nel.org>, kasan-dev@...glegroups.com,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Marco Elver <elver@...gle.com>, linux-media@...r.kernel.org,
        linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] [RFC] ubsan: disallow bounds checking with gcov on
 broken gcc

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