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

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Date:   Thu, 14 Mar 2019 08:23:13 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Andrea Arcangeli <aarcange@...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@...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>,
        Kees Cook <keescook@...omium.org>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users

On Thu, Mar 14, 2019 at 4:00 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> 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...).

please name _one_ BPF JIT bug that affected unprivileged user space.