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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Thu, 7 Jan 2021 00:40:23 +0100
Message-ID: <CAK8P3a1KUr-zOvxc0hN0yDC7r+HTM_FGrr5GkuSTTNchgQ0PzA@mail.gmail.com>
Subject: Re: [PATCH] ubsan: disable unsigned-integer-overflow sanitizer with clang
To:     Kees Cook <keescook@chromium.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marco Elver <elver@google.com>,
        George Popescu <georgepope@android.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Thu, Jan 7, 2021 at 12:17 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Wed, Jan 06, 2021 at 11:12:18PM +0100, Arnd Bergmann wrote:
> > On Wed, Jan 6, 2021 at 10:57 PM Kees Cook <keescook@chromium.org> wrote:
> > > On Wed, Dec 30, 2020 at 04:47:35PM +0100, Arnd Bergmann wrote:
> > > > diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> > > > index 8b635fd75fe4..e23873282ba7 100644
> > > > --- a/lib/Kconfig.ubsan
> > > > +++ b/lib/Kconfig.ubsan
> > > > @@ -122,6 +122,8 @@ config UBSAN_SIGNED_OVERFLOW
> > > >
> > > >  config UBSAN_UNSIGNED_OVERFLOW
> > > >       bool "Perform checking for unsigned arithmetic overflow"
> > > > +     # clang hugely expands stack usage with -fsanitize=object-size
> > > > +     depends on !CC_IS_CLANG
> > > >       depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
> > >
> > > Because of Clang implementation issues (see commit c637693b20da), this is
> > > already "default n" (and not supported under GCC at all). IIUC, setting
> > > this to "depends on !COMPILE_TEST" won't work for randconfigs, yes?
> >
> > Ah, I had not realized this is clang specific. Adding the !COMPILE_TEST
> > dependency would hide it for me, which may be good enough for me.
>
> I thought COMPILE_TEST does not get set for randconfig?

It does on my kernel, though I never submitted that patch ;-)

        Arnd