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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 12 Mar 2019 07:01:51 -0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x2C71oPe55771332 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 12 Mar 2019 07:01:50 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C76D34C194; Tue, 12 Mar 2019 07:01:50 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 237144C191; Tue, 12 Mar 2019 07:01:49 +0000 (GMT) Received: from rapoport-lnx (unknown [9.148.8.84]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Tue, 12 Mar 2019 07:01:49 +0000 (GMT) Date: Tue, 12 Mar 2019 09:01:47 +0200 From: Mike Rapoport To: Peter Xu 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 References: <20190311093701.15734-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190311093701.15734-1-peterx@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 19031207-0020-0000-0000-000003218323 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19031207-0021-0000-0000-00002173AB87 Message-Id: <20190312070147.GC9497@rapoport-lnx> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-12_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=736 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903120052 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: 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. Except for the comment to patch 1, feel free to add Reviewed-by: Mike Rapoport > All comments would be greatly welcomed. Thanks, > > Peter Xu (3): > userfaultfd/sysctl: introduce unprivileged_userfaultfd > kvm/mm: introduce MMF_USERFAULTFD_ALLOW flag > userfaultfd: apply unprivileged_userfaultfd check > > fs/userfaultfd.c | 121 +++++++++++++++++++++++++++++++++ > include/linux/sched/coredump.h | 1 + > include/linux/userfaultfd_k.h | 5 ++ > init/Kconfig | 11 +++ > kernel/sysctl.c | 11 +++ > virt/kvm/kvm_main.c | 7 ++ > 6 files changed, 156 insertions(+) > > -- > 2.17.1 > -- Sincerely yours, Mike.