linux-hardening - Re: [PATCH] gcc-plugins: Disable GCC_PLUGIN_CYC

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Date:   Tue, 23 Feb 2021 19:03:47 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH] gcc-plugins: Disable GCC_PLUGIN_CYC_COMPLEXITY for s390

On Tue, Feb 23, 2021 at 09:41:40AM -0800, Guenter Roeck wrote:
> > I tried to explain why we don't want to set COMPILE_TEST for s390
> > anymore. It overrides architecture dependencies in Kconfig, and lots
> > of drivers do not set dependencies for HAS_IOMEM, HAS_DMA, and friends
> > correctly.
> > This generates constantly fallout which is irrelevant for s390 and
> > also for other architectures. It generates just work with close to
> > zero benefit. For drivers which matter for s390 we still see those
> > errors.
> > 
> > > On the other side, if that flag would be set explicitly by
> > > all{yes,mod}config, it would really beg for being misused. We
> > > might then as well add a new flag that is explicitly associated
> > > with all{yes,mod}config, but not with randconfig.
> > 
> > I think that makes most sense, probably also have a flag that is set
> > for randconfig.
> 
> Not sure what value such an option would have, and how it would be used.
> I would argue that randconfig should not set COMPILE_TEST to start with,
> since its purpose should be to test random valid configurations and not
> to compile test arbitrary (and in that case random) code. But that is
> a different question, and just my personal opinion.
> 
> Overall, the question is what kind of additional option you would find
> useful for s390. You make it clear that you don't want COMPILE_TEST.
> At the same time, you still want all{mod,yes}config, but presumably
> excluding options currently restricted by !COMPILE_TEST (such as
> DEBUG_INFO, BPF_PRELOAD, UBSAN_TRAP, GCC_PLUGIN_CYC_COMPLEXITY,
> and a few others). SUPPRESS_NOISY_TESTS would not cover that, but
> neither would RANDCONFIG (or whatever it would be called).

Well, if we would have e.g. RANDCONFIG, then we could probably revert
334ef6ed06fa ("init/Kconfig: make COMPILE_TEST depend on !S390") and
instead let COMPILE_TEST depend on !RANDCONFIG.
I think this _could_ solve all common problems we currently see.

And it would also do what you suggested.