linux-hardening - Re: [RFC 0/3] kunit vs structleak

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Date:   Fri, 29 Jan 2021 13:29:20 -0800
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Alan Maguire <alan.maguire@...cle.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Vitor Massaru Iha <vitor@...saru.org>,
        linux-hardening@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>
Subject: Re: [RFC 0/3] kunit vs structleak

On Wed, Jan 27, 2021 at 12:15 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Jan 25, 2021 at 01:45:25PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > I ran into a couple of problems with kunit tests taking too much stack
> > space, sometimes dangerously so. These the the three instances that
> > cause an increase over the warning limit of some architectures:
> >
> > lib/bitfield_kunit.c:93:1: error: the frame size of 7440 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> > drivers/base/test/property-entry-test.c:481:1: error: the frame size of 2640 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> > drivers/thunderbolt/test.c:1529:1: error: the frame size of 1176 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> >
> > Ideally there should be a way to rewrite the kunit infrastructure
> > that avoids the explosion of stack data when the structleak plugin
> > is used.
> >
> > A rather drastic measure would be to use Kconfig logic to make
> > the two options mutually exclusive. This would clearly work, but
> > is probably not needed.
> >
> > As a simpler workaround, this disables the plugin for the three
> > files in which the excessive stack usage was observed.
> >
> >       Arnd
> >
> > Arnd Bergmann (3):
> >   bitfield: build kunit tests without structleak plugin
> >   drivers/base: build kunit tests without structleak plugin
> >   thunderbolt: build kunit tests without structleak plugin
> >
> >  drivers/base/test/Makefile   | 1 +
> >  drivers/thunderbolt/Makefile | 1 +
> >  lib/Makefile                 | 1 +
> >  3 files changed, 3 insertions(+)
>
> I think I'd prefer centralizing the disabling, as done with the other
> plugins, instead of sprinkling "open coded" command-line options around
> the kernel's Makefiles. :)
>
> For example:
>
>
> diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
> index 952e46876329..2d5009e3b593 100644
> --- a/scripts/Makefile.gcc-plugins
> +++ b/scripts/Makefile.gcc-plugins
> @@ -21,6 +21,10 @@ gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL)  \
>                 += -fplugin-arg-structleak_plugin-byref-all
>  gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK)              \
>                 += -DSTRUCTLEAK_PLUGIN
> +ifdef CONFIG_GCC_PLUGIN_STRUCTLEAK
> +    DISABLE_STRUCTLEAK_PLUGIN += -fplugin-arg-structleak_plugin-disable
> +endif
> +export DISABLE_STRUCTLEAK_PLUGIN
>
>  gcc-plugin-$(CONFIG_GCC_PLUGIN_RANDSTRUCT)     += randomize_layout_plugin.so
>  gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_RANDSTRUCT)              \
>
>
> And then use DISABLE_STRUCTLEAK_PLUGIN.

This looks fine to me. Does somebody want me to send this out as a
patch? Don't want to steal anyone's thunder :-)