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[209.132.183.28]) by mx.google.com with ESMTPS id s68si5166179qki.17.2019.03.12.05.29.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Mar 2019 05:29:39 -0700 (PDT) Received-SPF: pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0C073307CDEA; Tue, 12 Mar 2019 12:29:39 +0000 (UTC) Received: from xz-x1 (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 230E01001E6A; Tue, 12 Mar 2019 12:29:29 +0000 (UTC) Date: Tue, 12 Mar 2019 20:29:27 +0800 From: Peter Xu To: Mike Rapoport Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , Hugh Dickins , Luis Chamberlain , Maxime Coquelin , kvm@vger.kernel.org, Jerome Glisse , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Denis Plotnikov , linux-mm@kvack.org, Marty McFadden , Maya Gokhale , Mike Kravetz , Andrea Arcangeli , Mike Rapoport , Kees Cook , Mel Gorman , "Kirill A . Shutemov" , linux-fsdevel@vger.kernel.org, "Dr . David Alan Gilbert" , Andrew Morton Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users Message-ID: <20190312122927.GF14108@xz-x1> References: <20190311093701.15734-1-peterx@redhat.com> <20190312070147.GC9497@rapoport-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190312070147.GC9497@rapoport-lnx> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Tue, 12 Mar 2019 12:29:39 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Mar 12, 2019 at 09:01:47AM +0200, Mike Rapoport wrote: > Hi Peter, > > 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 > > > > - When set to "disabled", all unprivileged users are forbidden to > > use userfaultfd syscalls. > > > > - When set to "enabled", all users are allowed to use userfaultfd > > syscalls. > > > > - When set to "kvm", all unprivileged users are forbidden to use the > > userfaultfd syscalls, except the user who has permission to open > > /dev/kvm. > > > > This new flag can add one more layer of security to reduce the attack > > surface of the kernel by abusing userfaultfd. Here we grant the > > thread userfaultfd permission by checking against CAP_SYS_PTRACE > > capability. By default, the value is "disabled" which is the most > > strict policy. Distributions can have their own perferred value. > > > > The "kvm" entry is a bit special here only to make sure that existing > > users like QEMU/KVM won't break by this newly introduced flag. What > > we need to do is simply set the "unprivileged_userfaultfd" flag to > > "kvm" here to automatically grant userfaultfd permission for processes > > like QEMU/KVM without extra code to tweak these flags in the admin > > code. > > > > Patch 1: The interface patch to introduce the flag > > > > Patch 2: The KVM related changes to detect opening of /dev/kvm > > > > Patch 3: Apply the flag to userfaultfd syscalls > > I'd appreciate to see "Patch 4: documentation update" ;-) > It'd be also great to update the man pages after this is merged. Oops, sorry! I should have remembered that. > > Except for the comment to patch 1, feel free to add > > Reviewed-by: Mike Rapoport Thanks Mike! I'll take it for 2/3 until I got confirmation from you on patch 1. Regards, -- Peter Xu