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>,
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adilger kernel <adilger.kernel@dilger.ca>,
Ross Zwisler <zwisler@kernel.org>,
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lcapitulino@redhat.com, Kevin Wolf <kwolf@redhat.com>,
Nitesh Narayan Lal <nilal@redhat.com>,
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xiaoguangrong eric <xiaoguangrong.eric@gmail.com>,
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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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