linux-kernel - Re: [GIT PULL] x86/build changes for v4.17

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Date:   Thu, 5 Apr 2018 09:08:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     James Y Knight <jyknight@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        gregkh@...uxfoundation.org,
        Nick Desaulniers <ndesaulniers@...gle.com>, mka@...omium.org,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        tglx@...utronix.de, Andrew Morton <akpm@...ux-foundation.org>,
        Chandler Carruth <chandlerc@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Kees Cook <keescook@...gle.com>, groeck@...omium.org,
        Greg Hackmann <ghackmann@...gle.com>
Subject: Re: [GIT PULL] x86/build changes for v4.17

On Wed, Apr 04, 2018 at 10:21:05PM +0000, James Y Knight wrote:
> But allowing random pointer arithmetic, and pointer arithmetic wraparound,
> is still different than asserting that an object _field access_ can
> overflow. Clang does not believe that can happen -- it assumes that an
> object will still be contiguous. And that's why the llist stuff used to be
> broken, before it was corrected to do simply do math on a uintptr_t (which
> is a nice and simple and sane fix!).

That 'fix' wasn't anything simple, I recently ran into that
member_address_is_nonnull() trainwreck and had to think real hard wtf it
was about.