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

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Date:   Tue, 12 Mar 2019 20:43:02 +0800
From:   Peter Xu <peterx@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        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 Kravetz <mike.kravetz@...cle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Mel Gorman <mgorman@...e.de>, linux-fsdevel@...r.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-api@...r.kernel.org
Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users

Hi, Kirill,

On Tue, Mar 12, 2019 at 10:49:51AM +0300, Kirill A. Shutemov wrote:
> On Mon, Mar 11, 2019 at 05:36:58PM +0800, Peter Xu wrote:
> > Hi,
> > 
> > (The idea comes from Andrea, and following discussions with Mike and
> >  other people)
> > 
> > This patchset introduces a new sysctl flag to allow the admin to
> > forbid users from using userfaultfd:
> > 
> >   $ cat /proc/sys/vm/unprivileged_userfaultfd
> >   [disabled] enabled kvm
> 
> CC linux-api@
> 
> This is unusual way to return current value for sysctl. Does it work fine
> with sysctl tool?

It can work, though it displays the same as "cat":

$ sysctl vm.unprivileged_userfaultfd
vm.unprivileged_userfaultfd = disabled enabled [kvm] 

> 
> Have you considered to place the switch into /sys/kernel/mm instead?
> I doubt it's the last tunable for userfaultfd. Maybe we should have an
> directory for it under /sys/kernel/mm?

I haven't thought about sysfs, if that's preferred I can consider to
switch to that.  And yes I think creating a directory should be a good
idea.

Thanks,

-- 
Peter Xu