linux-kernel - Re: [PATCH] ubsan: disable unsigned-integer-overflow sanitizer with clang

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Message-ID: <202101061516.F0EA5F0@keescook>
Date:   Wed, 6 Jan 2021 15:17:33 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marco Elver <elver@...gle.com>,
        George Popescu <georgepope@...roid.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] ubsan: disable unsigned-integer-overflow sanitizer with
 clang

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@...omium.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?

> > Is there some better way to mark this as "known to have issues, please
> > don't include in randconfig?"
> >
> > I'd like to keep it around so people can continue to work out the
> > problems with it, but not have unexpecting folks trip over it. ;)
> 
> I've reverted that patch locally now and default-enabled for randconfigs.
> Now that I have an otherwise clean build, this should provide me
> with a full set of files that produce the warning. If the number is
> small enough, I could try opening individual github issues.

Okay, let me know if something needs changing. :)

-- 
Kees Cook