linux-kernel - Re: [PATCH v2 1/1] userfaultfd/sysctl: add vm.unprivileged

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Date:   Tue, 19 Mar 2019 11:02:36 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Peter Xu <peterx@...hat.com>
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>,
        Maya Gokhale <gokhale2@...l.gov>,
        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>,
        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>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH v2 1/1] userfaultfd/sysctl: add
 vm.unprivileged_userfaultfd

On Tue, 19 Mar 2019 11:07:22 +0800 Peter Xu <peterx@...hat.com> wrote:

> Add a global sysctl knob "vm.unprivileged_userfaultfd" to control
> whether userfaultfd is allowed by unprivileged users.  When this is
> set to zero, only privileged users (root user, or users with the
> CAP_SYS_PTRACE capability) will be able to use the userfaultfd
> syscalls.

Please send along a full description of why you believe Linux needs
this feature, for me to add to the changelog.  What is the benefit to
our users?  How will it be used?

etcetera.  As it was presented I'm seeing no justification for adding
the patch!