linux-kernel - Re: [PATCH 1/4] ubsan: Move cc-option tests into Kconfig

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Date:   Mon, 5 Oct 2020 23:01:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        George Popescu <georgepope@...roid.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        clang-built-linux@...glegroups.com, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] ubsan: Move cc-option tests into Kconfig

On Sun, Oct 04, 2020 at 12:08:47AM -0700, Nathan Chancellor wrote:
> On Fri, Oct 02, 2020 at 03:15:24PM -0700, Kees Cook wrote:
> > Instead of doing if/endif blocks with cc-option calls in the UBSAN
> > Makefile, move all the tests into Kconfig and use the Makefile to
> > collect the results.
> > 
> > Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Link: https://lore.kernel.org/lkml/CAHk-=wjPasyJrDuwDnpHJS2TuQfExwe=px-SzLeN8GFMAQJPmQ@mail.gmail.com/
> 
> I tested menuconfig to make sure all the flags when CONFIG_UBSAN_MISC is
> flipped.
> 
> Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> Tested-by: Nathan Chancellor <natechancellor@...il.com>

Awesome, thank you!

> One comment below.
> 
> > [...]
> > diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> > index 9716dab06bc7..72862da47baf 100644
> > --- a/scripts/Makefile.ubsan
> > +++ b/scripts/Makefile.ubsan
> > @@ -1,37 +1,21 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  
> > -export CFLAGS_UBSAN :=
> > +# -fsanitize=* options makes GCC less smart than usual and
> > +# increases the number of 'maybe-uninitialized' false-positives.
> > +ubsan-cflags-$(CONFIG_UBSAN) += $(call cc-disable-warning, maybe-uninitialized)
> 
> Is this just to force -Wno-maybe-uninitialized even when W=2?
> -Wmaybe-uninitialized is already disabled globally after
> commit 78a5255ffb6a ("Stop the ad-hoc games with
> -Wno-maybe-initialized"). I feel like it might be worth a comment in
> case that changes in the future but maybe that is a bit much.
> 
> > [...]
> > -      # -fsanitize=* options makes GCC less smart than usual and
> > -      # increase number of 'maybe-uninitialized false-positives
> > -      CFLAGS_UBSAN += $(call cc-option, -Wno-maybe-uninitialized)

It's just a direct copying of the existing logic, but into the new
"ubsan-cflags-y" style. But yes, AFAICT, that was the intent when it was
added in commit a76bcf557ef4 ("Kbuild: enable -Wmaybe-uninitialized
warning for "make W=1"").

So for this patch, I kept the logic as it was.

-- 
Kees Cook