Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20200302130430.201037-1-glider@google.com> <20200302130430.201037-2-glider@google.com>
 <20200302173852.GB109022@kroah.com>
In-Reply-To: <20200302173852.GB109022@kroah.com>
From:   Alexander Potapenko <glider@google.com>
Date:   Mon, 2 Mar 2020 19:28:03 +0100
Message-ID: <CAG_fn=WvA44J5fN=3i0WoOa-TK=1CqSrdCtR_ceZX0AzUM5s5A@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] binder: do not initialize locals passed to copy_from_user()
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Todd Kjos <tkjos@google.com>, Kees Cook <keescook@chromium.org>,
        =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>,
        Ingo Molnar <mingo@redhat.com>,
        Dmitriy Vyukov <dvyukov@google.com>,
        Jann Horn <jannh@google.com>,
        "open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Mar 2, 2020 at 6:38 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Mar 02, 2020 at 02:04:29PM +0100, glider@google.com wrote:
> > Certain copy_from_user() invocations in binder.c are known to
> > unconditionally initialize locals before their first use, like e.g. in
> > the following case:
> >
> >       struct binder_transaction_data tr;
> >       if (copy_from_user(&tr, ptr, sizeof(tr)))
> >               return -EFAULT;
> >
> > In such cases enabling CONFIG_INIT_STACK_ALL leads to insertion of
> > redundant locals initialization that the compiler fails to remove.
> > To work around this problem till Clang can deal with it, we apply
> > __no_initialize to local Binder structures.
>
> I would like to see actual benchmark numbers showing this is
> needed/useful otherwise it's going to just be random people adding this
> marking to random places with no real reason.
This were lib[hw]binder_benchmarks.
I will update patch description with benchmark data.
> thanks,
>
> greg k-h


--=20
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Stra=C3=9Fe, 33
80636 M=C3=BCnchen

Gesch=C3=A4ftsf=C3=BChrer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg