linux-kernel - Re: [PATCH v3 2/6] userfaultfd: add /dev/userfaultfd for fine grained access control

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Message-Id: <20220613145540.1c9f7750092911bae1332b92@linux-foundation.org>
Date:   Mon, 13 Jun 2022 14:55:40 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Charan Teja Reddy <charante@...eaurora.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Peter Xu <peterx@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        zhangyi <yi.zhang@...wei.com>, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 2/6] userfaultfd: add /dev/userfaultfd for fine
 grained access control

On Wed,  1 Jun 2022 14:09:47 -0700 Axel Rasmussen <axelrasmussen@...gle.com> wrote:

> To achieve this, add a /dev/userfaultfd misc device. This device
> provides an alternative to the userfaultfd(2) syscall for the creation
> of new userfaultfds. The idea is, any userfaultfds created this way will
> be able to handle kernel faults, without the caller having any special
> capabilities. Access to this mechanism is instead restricted using e.g.
> standard filesystem permissions.

The use of a /dev node isn't pretty.  Why can't this be done by
tweaking sys_userfaultfd() or by adding a sys_userfaultfd2()?

Peter, will you be completing review of this patchset?