Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220609221702.347522-1-morbo@google.com> <20220609152527.4ad7862d4126e276e6f76315@linux-foundation.org>
In-Reply-To: <20220609152527.4ad7862d4126e276e6f76315@linux-foundation.org>
From:   Bill Wendling <morbo@google.com>
Date:   Thu, 9 Jun 2022 15:49:21 -0700
Message-ID: <CAGG=3QXDt9AeCQOAp1311POFRSByJru4=Q=oFiQn3u2iZYk2_w@mail.gmail.com>
Subject: Re: [PATCH 00/12] Clang -Wformat warning fixes
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Bill Wendling <isanbard@gmail.com>,
        Tony Luck <tony.luck@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Phillip Potter <phil@philpotter.co.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Jan Kara <jack@suse.com>,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        Ross Philipson <ross.philipson@oracle.com>,
        Daniel Kiper <daniel.kiper@oracle.com>,
        linux-edac@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        linux-mm@kvack.org, netfilter-devel@vger.kernel.org,
        coreteam@netfilter.org, Networking <netdev@vger.kernel.org>,
        alsa-devel@alsa-project.org,
        clang-built-linux <llvm@lists.linux.dev>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Jun 9, 2022 at 3:25 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu,  9 Jun 2022 22:16:19 +0000 Bill Wendling <morbo@google.com> wrote:
>
> > This patch set fixes some clang warnings when -Wformat is enabled.
> >
>
> tldr:
>
> -       printk(msg);
> +       printk("%s", msg);
>
> the only reason to make this change is where `msg' could contain a `%'.
> Generally, it came from userspace.

It helps kernel developers not accidentally to insert an unescaped '%'
in their messages, potentially exposing their code to an attack
vector.

> Otherwise these changes are a
> useless consumer of runtime resources.

Calling a "printf" style function is already insanely expensive. :-) I
understand that it's not okay blithely to increase runtime resources
simply because it's already slow, but in this case it's worthwhile.

> I think it would be better to quieten clang in some fashion.

The "printk" and similar functions all have the "__printf" attribute.
I don't know of a modification to that attribute which can turn off
this type of check.

-bw