Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210812084348.6521-1-david@redhat.com> <87o8a2d0wf.fsf@disp2133>
 <60db2e61-6b00-44fa-b718-e4361fcc238c@www.fastmail.com> <87lf56bllc.fsf@disp2133>
 <CAHk-=wgru1UAm3kAKSOdnbewPXQMOxYkq9PnAsRadAC6pXCCMQ@mail.gmail.com>
 <87eeay8pqx.fsf@disp2133> <5b0d7c1e73ca43ef9ce6665fec6c4d7e@AcuMS.aculab.com>
 <87h7ft2j68.fsf@disp2133> <CAHk-=whmXTiGUzVrTP=mOPQrg-XOi3R-45hC4dQOqW4JmZdFUQ@mail.gmail.com>
 <b629cda1-becd-4725-b16c-13208ff478d3@www.fastmail.com>
In-Reply-To: <b629cda1-becd-4725-b16c-13208ff478d3@www.fastmail.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 13 Aug 2021 14:54:43 -1000
Message-ID: <CAHk-=wiJ0u33h2CXAO4b271Diik=z4jRt64=Gt6YV2jV4ef27g@mail.gmail.com>
Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE
To:     Andy Lutomirski <luto@kernel.org>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        David Laight <David.Laight@aculab.com>,
        David Hildenbrand <david@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Kees Cook <keescook@chromium.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Mike Rapoport <rppt@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Chinwen Chang <chinwen.chang@mediatek.com>,
        Michel Lespinasse <walken@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Huang Ying <ying.huang@intel.com>,
        Jann Horn <jannh@google.com>, Feng Tang <feng.tang@intel.com>,
        Kevin Brodsky <Kevin.Brodsky@arm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Shawn Anastasio <shawn@anastas.io>,
        Steven Price <steven.price@arm.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Jens Axboe <axboe@kernel.dk>,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        Peter Xu <peterx@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Marco Elver <elver@google.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        Nicolas Viennot <Nicolas.Viennot@twosigma.com>,
        Thomas Cedeno <thomascedeno@google.com>,
        Collin Fijalkovich <cfijalkovich@google.com>,
        Michal Hocko <mhocko@suse.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Chengguang Xu <cgxu519@mykernel.net>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <ckoenig.leichtzumerken@gmail.com>,
        "linux-unionfs@vger.kernel.org" <linux-unionfs@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "<linux-fsdevel@vger.kernel.org>" <linux-fsdevel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Florian Weimer <fweimer@redhat.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Aug 13, 2021 at 2:49 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> I=E2=80=99ll bite.  How about we attack this in the opposite direction: r=
emove the deny write mechanism entirely.

I think that would be ok, except I can see somebody relying on it.

It's broken, it's stupid, but we've done that ETXTBUSY for a _loong_ time.

But you are right that we have removed parts of it over time (no more
MAP_DENYWRITE, no more uselib()) so that what we have today is a
fairly weak form of what we used to do.

And nobody really complained when we weakened it, so maybe removing it
entirely might be acceptable.

              Linus