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Date:   Tue, 9 Feb 2021 16:21:21 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Andrey Rybainin <ryabinin.a.a@gmail.com>
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-kernel@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
        dvyukov@google.com
Subject: Re: [PATCH] ubsan: Require GCC-8+ or Clang to use UBSAN
Message-ID: <202102091619.8D6D5B4@keescook>
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On Wed, Feb 10, 2021 at 02:17:57AM +0300, Andrey Rybainin wrote:
> >>>> Subject: ubsan: Require GCC-8+ or Clang to use UBSAN
> >>>>
> >>>> Just like how we require GCC-8.2 for KASAN due to compiler bugs, require
> >>>> a sane version of GCC for UBSAN.
> >>>>
> >>>> Specifically, before GCC-8 UBSAN doesn't respect -fwrapv and thinks
> >>>> signed arithmetic is buggered.
> >>>
> >>> Actually removing CONFIG_UBSAN_SIGNED_OVERFLOW would give us the same
> >>> effect without restricting GCC versions.
> >>
> >> Is that preferable?  Always happy to remove code, just need some
> >> justification behind it.
> > 
> > Is Peter's patch acceptable or do you want to do something else?
> 
> I do prefer to just remove the code, I'll send the patch shortly.

I have a specific goal of getting both signed and unsigned overflow
detection working sanely, so removing this entirely from the kernel
really makes working on that difficult. :)

I view the primary problem as compiler-specific. I'd much rather we
correctly mask against versions (or better yet, behaviors).

-- 
Kees Cook