linux-kernel - Re: [PATCH v5 1/2] Add UFFD_USER_MODE

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Message-ID: <20201024020843.GB19707@redhat.com>
Date:   Fri, 23 Oct 2020 22:08:43 -0400
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Lokesh Gidra <lokeshgidra@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Jonathan Corbet <corbet@....net>, Peter Xu <peterx@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Daniel Colascione <dancol@...col.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kaleshsingh@...gle.com,
        calin@...gle.com, surenb@...gle.com, nnk@...gle.com,
        jeffv@...gle.com, kernel-team@...roid.com,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Shaohua Li <shli@...com>, Jerome Glisse <jglisse@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Nitin Gupta <nigupta@...dia.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Daniel Colascione <dancol@...gle.com>
Subject: Re: [PATCH v5 1/2] Add UFFD_USER_MODE_ONLY

On Sat, Oct 10, 2020 at 11:24:55PM -0700, Lokesh Gidra wrote:
> userfaultfd handles page faults from both user and kernel code.
> Add a new UFFD_USER_MODE_ONLY flag for userfaultfd(2) that makes
> the resulting userfaultfd object refuse to handle faults from kernel
> mode, treating these faults as if SIGBUS were always raised, causing
> the kernel code to fail with EFAULT.
> 
> A future patch adds a knob allowing administrators to give some
> processes the ability to create userfaultfd file objects only if they
> pass UFFD_USER_MODE_ONLY, reducing the likelihood that these processes
> will exploit userfaultfd's ability to delay kernel page faults to open
> timing windows for future exploits.
> 
> Signed-off-by: Daniel Colascione <dancol@...gle.com>
> Signed-off-by: Lokesh Gidra <lokeshgidra@...gle.com>

Reviewed-by: Andrea Arcangeli <aarcange@...hat.com>