Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221207154939.2532830-1-jeffxu@google.com> <20221207154939.2532830-4-jeffxu@google.com>
 <202212080821.5AE7EE99@keescook> <CALmYWFuKR538vHxqYH1p6mb9iShOohf5bpHZXSfUN4KQHYiwaA@mail.gmail.com>
 <Y5yS8wCnuYGLHMj4@x1n> <CALmYWFsDhX76zbcyhYAW-u0BBwD+m+TKpt4_pZTMt+22zHhrGQ@mail.gmail.com>
 <20221216094259.bec91e4abd6cf54a05ce2813@linux-foundation.org>
In-Reply-To: <20221216094259.bec91e4abd6cf54a05ce2813@linux-foundation.org>
From:   Jeff Xu <jeffxu@google.com>
Date:   Fri, 16 Dec 2022 10:11:44 -0800
Message-ID: <CALmYWFsNp87a5uVQUAb4PG0khFN8Xxd=ibh9Q7g-Y0XW1Mn-8Q@mail.gmail.com>
Subject: Re: [PATCH v6 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Peter Xu <peterx@redhat.com>, Kees Cook <keescook@chromium.org>,
        jeffxu@chromium.org, skhan@linuxfoundation.org,
        dmitry.torokhov@gmail.com, dverkamp@chromium.org, hughd@google.com,
        jorgelo@chromium.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
        jannh@google.com, linux-hardening@vger.kernel.org,
        kernel test robot <lkp@intel.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Dec 16, 2022 at 9:43 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Fri, 16 Dec 2022 09:15:40 -0800 Jeff Xu <jeffxu@google.com> wrote:
>
> > On Fri, Dec 16, 2022 at 7:47 AM Peter Xu <peterx@redhat.com> wrote:
> > >
> > > Hi, Jeff,
> > >
> > > On Thu, Dec 08, 2022 at 02:55:45PM -0800, Jeff Xu wrote:
> > > > > > +     if (!(flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
> > >
> > > [...]
> > >
> > > > > > +             pr_warn_ratelimited(
> > > > > > +                     "memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=%d '%s'\n",
> > > > > > +                     task_pid_nr(current), get_task_comm(comm, current));
> > >
> > > This will be frequently dumped right now with mm-unstable.  Is that what it
> > > wanted to achieve?
> > >
> > > [   10.822575] memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=491 'systemd'
> > > [   10.824743] memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=495 '(sd-executor)'
> > > ...
> > >
> > > If there's already a sane default value (and also knobs for the user to
> > > change the default) not sure whether it's saner to just keep it silent as
> > > before?
> > >
> > Thanks for your comments.
> >
> > The intention is it is a reminder to adjust API calls to explicitly
> > setting this bit.
>
> Do we need to warn more than once per boot?  If not, use pr_warn_once()?
>
Once per boot seems too little, it would be nice if we can list all processes.
I agree ratelimited might be too much.
There is a feature gap here for logging.

Kees, what do you think ?


> > The sysctl vm.memfd_noexec = 0 1 is for transaction to the final
> > state, and 2 depends on API call setting this bit.
> >
> > The log is ratelimited, and there is a rate limit setting:
> > /proc/sys/kernel/printk_ratelimit
> > /proc/sys/kernel/printk_ratelimit_burst
> >
>