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

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Date:   Thu, 14 Mar 2019 11:58:15 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Peter Xu <peterx@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Maxime Coquelin <maxime.coquelin@...hat.com>,
        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@...ck.org,
        Marty McFadden <mcfadden8@...l.gov>,
        Maya Gokhale <gokhale2@...l.gov>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        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 14/03/19 00:44, Andrea Arcangeli wrote:
> Then I thought we can add a tristate so an open of /dev/kvm would also
> allow the syscall to make things more user friendly because
> unprivileged containers ideally should have writable mounts done with
> nodev and no matter the privilege they shouldn't ever get an hold on
> the KVM driver (and those who do, like kubevirt, will then just work).

I wouldn't even bother with the KVM special case.  Containers can use
seccomp if they want a fine-grained policy.

(Actually I wouldn't bother with the knob at all; the attack surface of
userfaultfd is infinitesimal compared to the BPF JIT...).

Paolo