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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 23 Apr 2019 12:36:43 -0700
Message-ID: <CAGXu5jLNwFfG-x-_Q6nTdU21t5B9z7dCgBekRiJ+MnUE14J12A@mail.gmail.com>
Subject: Re: [PATCH v2 1/3] security: Create "kernel hardening" config area
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Alexander Potapenko <glider@google.com>,
        James Morris <jmorris@namei.org>,
        Alexander Popov <alex.popov@linux.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Kostya Serebryany <kcc@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Sandeep Patil <sspatil@android.com>,
        Laura Abbott <labbott@redhat.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Emese Revfy <re.emese@gmail.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Apr 11, 2019 at 6:39 PM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> On Fri, Apr 12, 2019 at 3:01 AM Kees Cook <keescook@chromium.org> wrote:
> >
> > Right now kernel hardening options are scattered around various Kconfig
> > files. This can be a central place to collect these kinds of options
> > going forward. This is initially populated with the memory initialization
> > options from the gcc-plugins.
> >
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  scripts/gcc-plugins/Kconfig | 74 +++--------------------------
> >  security/Kconfig            |  2 +
> >  security/Kconfig.hardening  | 93 +++++++++++++++++++++++++++++++++++++
> >  3 files changed, 102 insertions(+), 67 deletions(-)
> >  create mode 100644 security/Kconfig.hardening
> >
> > diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
> > index 74271dba4f94..84d471dea2b7 100644
> > --- a/scripts/gcc-plugins/Kconfig
> > +++ b/scripts/gcc-plugins/Kconfig
> > @@ -13,10 +13,11 @@ config HAVE_GCC_PLUGINS
> >           An arch should select this symbol if it supports building with
> >           GCC plugins.
> >
> > -menuconfig GCC_PLUGINS
> > -       bool "GCC plugins"
> > +config GCC_PLUGINS
> > +       bool
> >         depends on HAVE_GCC_PLUGINS
> >         depends on PLUGIN_HOSTCC != ""
> > +       default y
> >         help
> >           GCC plugins are loadable modules that provide extra features to the
> >           compiler. They are useful for runtime instrumentation and static analysis.
> > @@ -25,6 +26,8 @@ menuconfig GCC_PLUGINS
> >
> >  if GCC_PLUGINS
> >
> > +menu "GCC plugins"
> > +
>
>
>
> Just a tip to save "if" ... "endif" block.
>
>
> If you like, you can write like follows:
>
>
> menu "GCC plugins"
>           depends on GCC_PLUGINS
>
>   <menu body>
>
> endmenu

Ah yes, thanks! Adjusted.

> > +menu "Memory initialization"
> > +
> > +choice
> > +       prompt "Initialize kernel stack variables at function entry"
> > +       depends on GCC_PLUGINS
>
> On second thought,
> this 'depends on' is unnecessary
> because INIT_STACK_NONE should be always visible.

Oh yes, excellent point. Adjusted.

> Another behavior change is
> GCC_PLUGIN_STRUCTLEAK was previously enabled by all{yes,mod}config,
> and in the compile-test coverage.

I could set the defaults based on CONFIG_COMPILE_TEST, though? I.e.:

        prompt "Initialize kernel stack variables at function entry"
        default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
        default INIT_STACK_ALL if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT
        default INIT_STACK_NONE

>
> It will be disabled for all{yes,mod}config with this patch.
>
> This is up to you. Just FYI.

Thanks for looking this over!

-- 
Kees Cook