linux-kernel - Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users

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Message-ID: <CAGXu5j+WwcYTavVRp2M1AashdCwf2YX=RmUtO_5bHXPK9iZhGQ@mail.gmail.com>
Date:   Fri, 15 Mar 2019 09:09:45 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Maxime Coquelin <maxime.coquelin@...hat.com>,
        KVM <kvm@...r.kernel.org>, Jerome Glisse <jglisse@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Cracauer <cracauer@...s.org>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Linux-MM <linux-mm@...ck.org>,
        Marty McFadden <mcfadden8@...l.gov>,
        Maya Gokhale <gokhale2@...l.gov>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users

On Thu, Mar 14, 2019 at 9:16 AM Andrea Arcangeli <aarcange@...hat.com> wrote:
> So this will be for who's paranoid and prefers to disable userfaultfd
> as a whole as an hardening feature like the bpf sysctl allows: it will
> allow to block uffd syscall without having to rebuild the kernel with
> CONFIG_USERFAULTFD=n in environments where seccomp cannot be easily
> enabled (i.e. without requiring userland changes).
>
> That's very fine with me, but then it wasn't me complaining in the
> first place. Kees?

I'm fine with a boolean. I just wanted to find a way to disable at
runtime (so distro users had it available to them).

-- 
Kees Cook