linux-hardening - Re: [PATCH v6 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD

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Message-ID: <CALmYWFsNp87a5uVQUAb4PG0khFN8Xxd=ibh9Q7g-Y0XW1Mn-8Q@mail.gmail.com>
Date:   Fri, 16 Dec 2022 10:11:44 -0800
From:   Jeff Xu <jeffxu@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Peter Xu <peterx@...hat.com>, Kees Cook <keescook@...omium.org>,
        jeffxu@...omium.org, skhan@...uxfoundation.org,
        dmitry.torokhov@...il.com, dverkamp@...omium.org, hughd@...gle.com,
        jorgelo@...omium.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        jannh@...gle.com, linux-hardening@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v6 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC

On Fri, Dec 16, 2022 at 9:43 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Fri, 16 Dec 2022 09:15:40 -0800 Jeff Xu <jeffxu@...gle.com> wrote:
>
> > On Fri, Dec 16, 2022 at 7:47 AM Peter Xu <peterx@...hat.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
> >
>