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Message-ID: <CAK7LNAS+=hWM=CvMKMWNa0Fb4S7XL6yPBCQ=TnpM2REsuOYniQ@mail.gmail.com>
Date: Mon, 20 Apr 2020 07:34:53 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Kees Cook <keescook@...omium.org>, Emese Revfy <re.emese@...il.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Cc: Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
David Lamparter <equinox@...c24.net>
Subject: Re: gcc extended format checking plugin
FW: GCC-plugin maintainers
On Mon, Apr 20, 2020 at 7:04 AM David Lamparter <equinox@...c24.net> wrote:
>
> Hello kernel build hackers,
>
>
> in case it is of interest to anyone, we've recently added an extended
> format string checking plugin in the FRRouting project. We took
> inspiration from the Linux kernel and modified a printf (funnily enough,
> the one from FreeBSD) to support things like %pI4, and we wanted better
> warnings for this. Since the scheme is the same as in the Linux kernel,
> it may or may not be worth someone's time to take a look.
>
> The plugin is found here:
> https://github.com/FRRouting/frr/tree/master/tools/gcc-plugins
>
> It's derived from gcc's "c-format.c", as such it may make sense to look
> at the diff instead of the straight source. The original GCC code is in
> the git history there. It's tested against gcc 9.3.0, YMMV on other
> versions.
>
> Note that the plugin needs a single-line GCC source code modification:
> https://github.com/FRRouting/frr/blob/master/tools/gcc-plugins/gcc-retain-typeinfo.patch
> this is to stop GCC from prematurely stripping information, specifically
> from casts in function parameters. It does work without the change, but
> it may produce false-positive/negative warnings.
>
> Aside from %pXX suffix support, the plugin also contains two other
> changes that are probably irrelevant to kernel land:
> - it makes some typedefs "final" types since these are not guaranteed to
> be consistent in size across platforms and therefore can't be
> printf'd without a cast (e.g. pid_t, uid_t, time_t, etc.)
> - it reserves %Lu for uint64_t
>
> Please don't expect too much on its code quality, I'm not a GCC
> developer and essentially wrote this by trial and error ;)
>
> Cheers,
>
>
> -David
--
Best Regards
Masahiro Yamada
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