linux-kernel - Re: [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API.

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Message-ID: <20191023232708.GA433@redhat.com>
Date:   Wed, 23 Oct 2019 19:27:08 -0400
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>, Jann Horn <jannh@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Nick Kralevich <nnk@...gle.com>,
        Nosh Minwalla <nosh@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API.

On Wed, Oct 23, 2019 at 04:01:53PM -0700, Andy Lutomirski wrote:
> Delivering events through read() is just fine. The problem is when
> delivering an event does more than just returning bytes. As far as
> I’ve noticed, uffd’s read() just returns bytes as long as FORK is
> disabled.

Yes, fork is the only case where read doesn't return bytes.

Moving only the fd creation to a separate syscall would then avoid
involuntary creation of the fd.