linux-hardening - Re: [PATCH 2/2] gcc-plugins: Remove cyc

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Date:   Wed, 20 Oct 2021 12:10:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        linux-hardening@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-doc@...r.kernel.org, Dan Li <ashimida@...ux.alibaba.com>,
        ardb@...nel.org, ojeda@...nel.org,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 2/2] gcc-plugins: Remove cyc_complexity

On Wed, Oct 20, 2021 at 10:48:59AM -0700, Nathan Chancellor wrote:
> On Wed, Oct 20, 2021 at 10:35:54AM -0700, Kees Cook wrote:
> > This plugin has no impact on the resulting binary, is disabled
> > under COMPILE_TEST, and is not enabled on any builds I'm aware of.
> > Additionally, given the clarified purpose of GCC plugins in the kernel,
> > remove cyc_complexity.
> > 
> > Cc: Masahiro Yamada <masahiroy@...nel.org>
> > Cc: Michal Marek <michal.lkml@...kovi.net>
> > Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: linux-hardening@...r.kernel.org
> > Cc: linux-kbuild@...r.kernel.org
> > Cc: linux-doc@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> 
> One comment below.
> 
> > ---
> >  Documentation/kbuild/gcc-plugins.rst        |  2 -
> >  scripts/Makefile.gcc-plugins                |  2 -
> >  scripts/gcc-plugins/Kconfig                 | 16 -----
> >  scripts/gcc-plugins/cyc_complexity_plugin.c | 69 ---------------------
> >  4 files changed, 89 deletions(-)
> >  delete mode 100644 scripts/gcc-plugins/cyc_complexity_plugin.c
> > 
> > diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst
> > index 4b28c7a4032f..0ba76719f1b9 100644
> > --- a/Documentation/kbuild/gcc-plugins.rst
> > +++ b/Documentation/kbuild/gcc-plugins.rst
> > @@ -96,7 +96,6 @@ Enable the GCC plugin infrastructure and some plugin(s) you want to use
> >  in the kernel config::
> >  
> >  	CONFIG_GCC_PLUGINS=y
> > -	CONFIG_GCC_PLUGIN_CYC_COMPLEXITY=y
> >  	CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y
> >  	...
> >  
> 
> There is a comment about the cyc_complexity plugin at the very end of
> this file that should also be removed it seems:
> 
> "See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin."

Yup; I think it was hiding from you, see here:

> 
> > @@ -115,4 +114,3 @@ The GCC plugins are in scripts/gcc-plugins/. You need to put plugin source files
> >  right under scripts/gcc-plugins/. Creating subdirectories is not supported.
> >  It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins
> >  and a relevant Kconfig file.
> > -See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.
    ^^^^

:)

Thanks!

-Kees

-- 
Kees Cook