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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
> 
> 

  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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