From: Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> To: "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Cc: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>, KVM list <kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, David Hildenbrand <david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-nvdimm <linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org>, Jason Wang <jasowang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org>, Qemu Developers <qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org>, virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, adilger kernel <adilger.kernel-m1MBpc4rdrD3fQ9qLvQP4Q@public.gmane.org>, Ross Zwisler <zwisler-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, darrick wong <darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>, Matthew Wilcox <willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Linux ACPI <linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, linux-ext4 <linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Rik van Riel <riel-ebMLmSuQjDVBDgjK7y7TUQ@public.gmane.org>, Stefan Hajnoczi <stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Paolo Bonzini <pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, lcapitulino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Kevin Wolf <kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Nitesh Narayan Lal <nilal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org>, xiaoguangrong eric <xiaoguangrong.eric-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "Rafael J. Wysocki" <rjw@rjwyso Subject: Re: [Qemu-devel] [PATCH v3 0/5] kvm "virtio pmem" device Date: Tue, 15 Jan 2019 00:37:22 -0500 (EST) [thread overview] Message-ID: <208236727.64320322.1547530642536.JavaMail.zimbra@redhat.com> (raw) In-Reply-To: <20190114205031-mutt-send-email-mst-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> > > > > > > > > On Mon, Jan 14, 2019 at 02:15:40AM -0500, Pankaj Gupta wrote: > > > > > > > > > > > > Until you have images (and hence host page cache) shared between > > > > > > > multiple guests. People will want to do this, because it means > > > > > > > they > > > > > > > only need a single set of pages in host memory for executable > > > > > > > binaries rather than a set of pages per guest. Then you have > > > > > > > multiple guests being able to detect residency of the same set of > > > > > > > pages. If the guests can then, in any way, control eviction of > > > > > > > the > > > > > > > pages from the host cache, then we have a guest-to-guest > > > > > > > information > > > > > > > leak channel. > > > > > > > > > > > > I don't think we should ever be considering something that would > > > > > > allow a > > > > > > guest to evict page's from the host's pagecache [1]. The guest > > > > > > should > > > > > > be able to kick its own references to the host's pagecache out of > > > > > > its > > > > > > own pagecache, but not be able to influence whether the host or > > > > > > another > > > > > > guest has a read-only mapping cached. > > > > > > > > > > > > [1] Unless the guest is allowed to modify the host's file; > > > > > > obviously > > > > > > truncation, holepunching, etc are going to evict pages from the > > > > > > host's > > > > > > page cache. > > > > > > > > > > This is so correct. Guest does not not evict host page cache pages > > > > > directly. > > > > > > > > They don't right now. > > > > > > > > But someone is going to end up asking for discard to work so that > > > > the guest can free unused space in the underlying spares image (i.e. > > > > make use of fstrim or mount -o discard) because they have workloads > > > > that have bursts of space usage and they need to trim the image > > > > files afterwards to keep their overall space usage under control. > > > > > > > > And then.... > > > > > > ...we reject / push back on that patch citing the above concern. > > > > So at what point do we draw the line? > > > > We're allowing writable DAX mappings, but as I've pointed out that > > means we are going to be allowing a potential information leak via > > files with shared extents to be directly mapped and written to. > > > > But we won't allow useful admin operations that allow better > > management of host side storage space similar to how normal image > > files are used by guests because it's an information leak vector? > > > > That's splitting some really fine hairs there... > > May I summarize that th security implications need to > be documented? > > In fact that would make a fine security implications section > in the device specification. This is a very good suggestion. I will document the security implications in details in device specification with details of what all filesystem features we don't support and why. Best regards, Pankaj > > > > > > > > > > In case of virtio-pmem & DAX, guest clears guest page cache > > > > > exceptional entries. > > > > > Its solely decision of host to take action on the host page cache > > > > > pages. > > > > > > > > > > In case of virtio-pmem, guest does not modify host file directly i.e > > > > > don't > > > > > perform hole punch & truncation operation directly on host file. > > > > > > > > ... this will no longer be true, and the nuclear landmine in this > > > > driver interface will have been armed.... > > > > > > I agree with the need to be careful when / if explicit cache control > > > is added, but that's not the case today. > > > > "if"? > > > > I expect it to be "when", not if. Expect the worst, plan for it now. > > > > Cheers, > > > > Dave. > > -- > > Dave Chinner > > david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org > >
WARNING: multiple messages have this Message-ID (diff)
From: Pankaj Gupta <pagupta@redhat.com> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>, KVM list <kvm@vger.kernel.org>, David Hildenbrand <david@redhat.com>, linux-nvdimm <linux-nvdimm@ml01.01.org>, Jason Wang <jasowang@redhat.com>, Qemu Developers <qemu-devel@nongnu.org>, virtualization@lists.linux-foundation.org, adilger kernel <adilger.kernel@dilger.ca>, Ross Zwisler <zwisler@kernel.org>, dave jiang <dave.jiang@intel.com>, darrick wong <darrick.wong@oracle.com>, vishal l verma <vishal.l.verma@intel.com>, Matthew Wilcox <willy@infradead.org>, Christoph Hellwig <hch@infradead.org>, Linux ACPI <linux-acpi@vger.kernel.org>, jmoyer <jmoyer@redhat.com>, linux-ext4 <linux-ext4@vger.kernel.org>, Rik van Riel <riel@surriel.com>, Stefan Hajnoczi <stefanha@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Dan Williams <dan.j.williams@intel.com>, lcapitulino@redhat.com, Kevin Wolf <kwolf@redhat.com>, Nitesh Narayan Lal <nilal@redhat.com>, Theodore Ts'o <tytso@mit.edu>, xiaoguangrong eric <xiaoguangrong.eric@gmail.com>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-xfs <linux-xfs@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Paolo Bonzini <pbonzini@redhat.com> Subject: Re: [Qemu-devel] [PATCH v3 0/5] kvm "virtio pmem" device Date: Tue, 15 Jan 2019 00:37:22 -0500 (EST) [thread overview] Message-ID: <208236727.64320322.1547530642536.JavaMail.zimbra@redhat.com> (raw) Message-ID: <20190115053722.o8oY_ddGWhRApkjxxrnwf_RNIouGMzdKBcx-p6_4ack@z> (raw) In-Reply-To: <20190114205031-mutt-send-email-mst@kernel.org> > > > > > > > > On Mon, Jan 14, 2019 at 02:15:40AM -0500, Pankaj Gupta wrote: > > > > > > > > > > > > Until you have images (and hence host page cache) shared between > > > > > > > multiple guests. People will want to do this, because it means > > > > > > > they > > > > > > > only need a single set of pages in host memory for executable > > > > > > > binaries rather than a set of pages per guest. Then you have > > > > > > > multiple guests being able to detect residency of the same set of > > > > > > > pages. If the guests can then, in any way, control eviction of > > > > > > > the > > > > > > > pages from the host cache, then we have a guest-to-guest > > > > > > > information > > > > > > > leak channel. > > > > > > > > > > > > I don't think we should ever be considering something that would > > > > > > allow a > > > > > > guest to evict page's from the host's pagecache [1]. The guest > > > > > > should > > > > > > be able to kick its own references to the host's pagecache out of > > > > > > its > > > > > > own pagecache, but not be able to influence whether the host or > > > > > > another > > > > > > guest has a read-only mapping cached. > > > > > > > > > > > > [1] Unless the guest is allowed to modify the host's file; > > > > > > obviously > > > > > > truncation, holepunching, etc are going to evict pages from the > > > > > > host's > > > > > > page cache. > > > > > > > > > > This is so correct. Guest does not not evict host page cache pages > > > > > directly. > > > > > > > > They don't right now. > > > > > > > > But someone is going to end up asking for discard to work so that > > > > the guest can free unused space in the underlying spares image (i.e. > > > > make use of fstrim or mount -o discard) because they have workloads > > > > that have bursts of space usage and they need to trim the image > > > > files afterwards to keep their overall space usage under control. > > > > > > > > And then.... > > > > > > ...we reject / push back on that patch citing the above concern. > > > > So at what point do we draw the line? > > > > We're allowing writable DAX mappings, but as I've pointed out that > > means we are going to be allowing a potential information leak via > > files with shared extents to be directly mapped and written to. > > > > But we won't allow useful admin operations that allow better > > management of host side storage space similar to how normal image > > files are used by guests because it's an information leak vector? > > > > That's splitting some really fine hairs there... > > May I summarize that th security implications need to > be documented? > > In fact that would make a fine security implications section > in the device specification. This is a very good suggestion. I will document the security implications in details in device specification with details of what all filesystem features we don't support and why. Best regards, Pankaj > > > > > > > > > > In case of virtio-pmem & DAX, guest clears guest page cache > > > > > exceptional entries. > > > > > Its solely decision of host to take action on the host page cache > > > > > pages. > > > > > > > > > > In case of virtio-pmem, guest does not modify host file directly i.e > > > > > don't > > > > > perform hole punch & truncation operation directly on host file. > > > > > > > > ... this will no longer be true, and the nuclear landmine in this > > > > driver interface will have been armed.... > > > > > > I agree with the need to be careful when / if explicit cache control > > > is added, but that's not the case today. > > > > "if"? > > > > I expect it to be "when", not if. Expect the worst, plan for it now. > > > > Cheers, > > > > Dave. > > -- > > Dave Chinner > > david@fromorbit.com > >
next prev parent reply other threads:[~2019-01-15 5:37 UTC|newest] Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-01-09 14:47 [PATCH v3 0/5] kvm "virtio pmem" device Pankaj Gupta 2019-01-09 14:47 ` [PATCH v3 1/5] libnvdimm: nd_region flush callback support Pankaj Gupta 2019-01-09 14:47 ` [PATCH v3 2/5] virtio-pmem: Add virtio pmem driver Pankaj Gupta 2019-01-14 15:54 ` Michael S. Tsirkin 2019-01-14 15:54 ` Michael S. Tsirkin [not found] ` <20190114105314-mutt-send-email-mst-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 2019-01-15 6:33 ` Pankaj Gupta 2019-01-15 6:33 ` Pankaj Gupta 2019-01-09 14:47 ` [PATCH v3 3/5] libnvdimm: add nd_region buffered dax_dev flag Pankaj Gupta 2019-01-09 14:47 ` [PATCH v3 4/5] ext4: disable map_sync for virtio pmem Pankaj Gupta 2019-01-09 14:47 ` [PATCH v3 5/5] xfs: " Pankaj Gupta 2019-01-09 14:47 ` Pankaj Gupta 2019-01-09 16:26 ` Darrick J. Wong 2019-01-09 18:08 ` Pankaj Gupta [not found] ` <20190109144736.17452-1-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2019-01-10 1:26 ` [PATCH v3 0/5] kvm "virtio pmem" device Dave Chinner 2019-01-10 1:26 ` Dave Chinner 2019-01-10 2:40 ` Rik van Riel 2019-01-10 2:40 ` Rik van Riel 2019-01-10 10:17 ` Jan Kara 2019-01-10 10:17 ` Jan Kara [not found] ` <20190110101757.GC15790-4I4JzKEfoa/jFM9bn6wA6Q@public.gmane.org> 2019-01-13 1:38 ` Pankaj Gupta 2019-01-13 1:38 ` Pankaj Gupta [not found] ` <1354249849.63357171.1547343519970.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2019-01-13 1:43 ` Dan Williams 2019-01-13 1:43 ` Dan Williams [not found] ` <CAPcyv4hwcgTUpgNCefCGu4DvgkYBp5b=f+hJ+FC=s5APYKoycg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2019-01-13 2:17 ` [Qemu-devel] " Pankaj Gupta 2019-01-13 2:17 ` Pankaj Gupta [not found] ` <540171952.63371441.1547345866585.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2019-01-14 9:55 ` Jan Kara 2019-01-14 9:55 ` Jan Kara [not found] ` <20190114095520.GC13316-4I4JzKEfoa/jFM9bn6wA6Q@public.gmane.org> 2019-01-14 10:16 ` Pankaj Gupta 2019-01-14 10:16 ` Pankaj Gupta 2019-01-11 7:45 ` Pankaj Gupta 2019-01-11 7:45 ` Pankaj Gupta [not found] ` <1326478078.61913951.1547192704870.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2019-01-13 23:29 ` Dave Chinner 2019-01-13 23:29 ` Dave Chinner 2019-01-13 23:38 ` Matthew Wilcox 2019-01-13 23:38 ` Matthew Wilcox [not found] ` <20190113233820.GX6310-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org> 2019-01-14 2:50 ` Dave Chinner 2019-01-14 2:50 ` Dave Chinner 2019-01-14 7:15 ` Pankaj Gupta 2019-01-14 7:15 ` Pankaj Gupta [not found] ` <942065073.64011540.1547450140670.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2019-01-14 21:25 ` Dave Chinner 2019-01-14 21:25 ` Dave Chinner 2019-01-14 21:35 ` Dan Williams 2019-01-14 21:35 ` Dan Williams [not found] ` <CAPcyv4jtPcLV-s0sKNHwwk0ug7GLBV6699dpm1h3r2xSo879dg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2019-01-14 22:21 ` Dave Chinner 2019-01-14 22:21 ` Dave Chinner 2019-01-15 2:19 ` Michael S. Tsirkin 2019-01-15 2:19 ` Michael S. Tsirkin [not found] ` <20190114205031-mutt-send-email-mst-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 2019-01-15 5:37 ` Pankaj Gupta [this message] 2019-01-15 5:37 ` [Qemu-devel] " Pankaj Gupta 2019-01-15 5:35 ` Pankaj Gupta 2019-01-15 5:35 ` Pankaj Gupta [not found] ` <1684638419.64320214.1547530506805.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2019-01-15 20:42 ` Dave Chinner 2019-01-15 20:42 ` Dave Chinner 2019-02-04 22:56 ` security implications of caching with virtio pmem (was Re: [PATCH v3 0/5] kvm "virtio pmem" device) Michael S. Tsirkin 2019-02-05 7:29 ` [Qemu-devel] " Pankaj Gupta 2019-02-06 14:00 ` David Hildenbrand 2019-02-06 18:01 ` Michael S. Tsirkin 2019-02-11 7:29 ` [Qemu-devel] " Pankaj Gupta 2019-02-11 22:29 ` Dave Chinner 2019-02-11 22:58 ` David Hildenbrand 2019-02-11 23:07 ` Michael S. Tsirkin -- strict thread matches above, loose matches on Subject: below -- 2019-01-09 13:50 [PATCH v3 0/5] kvm "virtio pmem" device Pankaj Gupta 2019-01-09 14:46 ` [Qemu-devel] " Pankaj Gupta
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