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From:   Andy Lutomirski <luto@kernel.org>
Date:   Sat, 12 Oct 2019 16:10:16 -0700
Message-ID: <CALCETrVZHd+csdRL-uKbVN3Z7yeNNtxiDy-UsutMi=K3ZgCiYw@mail.gmail.com>
Subject: Re: [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API.
To:     Daniel Colascione <dancol@google.com>
Cc:     Linux API <linux-api@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, lokeshgidra@google.com,
        Nick Kralevich <nnk@google.com>, nosh@google.com,
        Tim Murray <timmurray@google.com>
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On Sat, Oct 12, 2019 at 12:16 PM Daniel Colascione <dancol@google.com> wrote:
>
> The new secure flag makes userfaultfd use a new "secure" anonymous
> file object instead of the default one, letting security modules
> supervise userfaultfd use.
>
> Requiring that users pass a new flag lets us avoid changing the
> semantics for existing callers.

Is there any good reason not to make this be the default?

The only downside I can see is that it would increase the memory usage
of userfaultfd(), but that doesn't seem like such a big deal.  A
lighter-weight alternative would be to have a single inode shared by
all userfaultfd instances, which would require a somewhat different
internal anon_inode API.

In any event, I don't think that "make me visible to SELinux" should
be a choice that user code makes.

--Andy