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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 1 Jun 2020 16:48:29 -0700
Message-ID: <CAKwvOd=BgiaiWWkHX=Z4OX927KNGu1CTnvVkhKRJ=vRTQKbu8Q@mail.gmail.com>
Subject: Re: [PATCH] ACPICA: fix UBSAN warning using __builtin_offsetof
To:     Peter Collingbourne <pcc@google.com>
Cc:     Robert Moore <robert.moore@intel.com>,
        Erik Kaneda <erik.kaneda@intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Len Brown <lenb@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Hanjun Guo <guohanjun@huawei.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Will Deacon <will@kernel.org>,
        "# 3.4.x" <stable@vger.kernel.org>, linux-acpi@vger.kernel.org,
        devel@acpica.org
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On Mon, Jun 1, 2020 at 4:37 PM Peter Collingbourne <pcc@google.com> wrote:
>
> On Mon, Jun 1, 2020 at 4:18 PM Nick Desaulniers <ndesaulniers@google.com> wrote:
> >
> > Will reported UBSAN warnings:
> > UBSAN: null-ptr-deref in drivers/acpi/acpica/tbfadt.c:459:37
> > UBSAN: null-ptr-deref in arch/arm64/kernel/smp.c:596:6
> >
> > Looks like the emulated offsetof macro ACPI_OFFSET is causing these. We
> > can avoid this by using the compiler builtin, __builtin_offsetof.
>
> Would it be better to s/ACPI_OFFSET/offsetof/g the existing users of
> this macro and remove it? It looks like offsetof is already being used
> pervasively in the kernel, and its definition comes from
> <linux/stddef.h>.

I count only 9 uses in the tree, so not too bad a yak shave. Good
idea; I'll send tomorrow short of any other feedback.  I still think
we want the builtin, since we don't want to include stddef.h in the
kernel, I think.
-- 
Thanks,
~Nick Desaulniers