Received-SPF: pass (google.com: domain of linux-kernel+bounces-188098-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Date: Thu, 23 May 2024 16:12:25 -0700
From: Kees Cook <keescook@chromium.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>, linux-kernel@vger.kernel.org,
	llvm@lists.linux.dev, patches@lists.linux.dev,
	kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] x86/boot: Address clang -Wimplicit-fallthrough in
 vsprintf()
Message-ID: <202405231603.2E810E3FC@keescook>
References: <20240516-x86-boot-fix-clang-implicit-fallthrough-v1-1-04dc320ca07c@kernel.org>
 <20240517095110.GAZkcojmJQoY_zU-OT@fat_crate.local>
 <20240517151833.GB3660288@thelio-3990X>
 <20240523115734.GAZk8vLgzOzD8Tv9pq@fat_crate.local>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240523115734.GAZk8vLgzOzD8Tv9pq@fat_crate.local>

On Thu, May 23, 2024 at 01:57:34PM +0200, Borislav Petkov wrote:
> On Fri, May 17, 2024 at 08:18:33AM -0700, Nathan Chancellor wrote:
> > There was a patch to make Clang match GCC's behavior a few years ago but
> > I think Kees made a good argument that GCC's behavior leaves potential
> > bugs on the table, so that was not pursued further.
> > 
> > https://reviews.llvm.org/D91895#2417170
> 
> Really? Maybe I'm being dense but I don't see real bugs there... I see
> readability issues. :-)

There isn't a bug _here_, but this is about making the code unambiguous
everywhere in the kernel. We've already done the work to get rid of
all these warnings; this one is newly introduced, so let's get it fixed.

We don't want to have the same flow-control statement reachable from two
different "case"s where the resulting behaviors are different. Otherwise
we can't determine if a "fallthrough" is missing or intentional.

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

-- 
Kees Cook