From: Stefan Hajnoczi <stefanha@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: "Yongji Xie" <xieyongji@bytedance.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
"Stefano Garzarella" <sgarzare@redhat.com>,
"Parav Pandit" <parav@nvidia.com>,
"Christoph Hellwig" <hch@infradead.org>,
"Christian Brauner" <christian.brauner@canonical.com>,
"Randy Dunlap" <rdunlap@infradead.org>,
"Matthew Wilcox" <willy@infradead.org>,
viro@zeniv.linux.org.uk, "Jens Axboe" <axboe@kernel.dk>,
bcrl@kvack.org, "Jonathan Corbet" <corbet@lwn.net>,
"Mika Penttilä" <mika.penttila@nextfour.com>,
"Dan Carpenter" <dan.carpenter@oracle.com>,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, kvm@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v6 10/10] Documentation: Add documentation for VDUSE
Date: Thu, 15 Apr 2021 15:38:26 +0100 [thread overview]
Message-ID: <YHhP4i+yXgA2KkVJ@stefanha-x1.localdomain> (raw)
In-Reply-To: <80b31814-9e41-3153-7efb-c0c2fab44feb@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 5389 bytes --]
On Thu, Apr 15, 2021 at 04:36:35PM +0800, Jason Wang wrote:
>
> 在 2021/4/15 下午3:19, Stefan Hajnoczi 写道:
> > On Thu, Apr 15, 2021 at 01:38:37PM +0800, Yongji Xie wrote:
> > > On Wed, Apr 14, 2021 at 10:15 PM Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > > > On Wed, Mar 31, 2021 at 04:05:19PM +0800, Xie Yongji wrote:
> > > > > VDUSE (vDPA Device in Userspace) is a framework to support
> > > > > implementing software-emulated vDPA devices in userspace. This
> > > > > document is intended to clarify the VDUSE design and usage.
> > > > >
> > > > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> > > > > ---
> > > > > Documentation/userspace-api/index.rst | 1 +
> > > > > Documentation/userspace-api/vduse.rst | 212 ++++++++++++++++++++++++++++++++++
> > > > > 2 files changed, 213 insertions(+)
> > > > > create mode 100644 Documentation/userspace-api/vduse.rst
> > > > Just looking over the documentation briefly (I haven't studied the code
> > > > yet)...
> > > >
> > > Thank you!
> > >
> > > > > +How VDUSE works
> > > > > +------------
> > > > > +Each userspace vDPA device is created by the VDUSE_CREATE_DEV ioctl on
> > > > > +the character device (/dev/vduse/control). Then a device file with the
> > > > > +specified name (/dev/vduse/$NAME) will appear, which can be used to
> > > > > +implement the userspace vDPA device's control path and data path.
> > > > These steps are taken after sending the VDPA_CMD_DEV_NEW netlink
> > > > message? (Please consider reordering the documentation to make it clear
> > > > what the sequence of steps are.)
> > > >
> > > No, VDUSE devices should be created before sending the
> > > VDPA_CMD_DEV_NEW netlink messages which might produce I/Os to VDUSE.
> > I see. Please include an overview of the steps before going into detail.
> > Something like:
> >
> > VDUSE devices are started as follows:
> >
> > 1. Create a new VDUSE instance with ioctl(VDUSE_CREATE_DEV) on
> > /dev/vduse/control.
> >
> > 2. Begin processing VDUSE messages from /dev/vduse/$NAME. The first
> > messages will arrive while attaching the VDUSE instance to vDPA.
> >
> > 3. Send the VDPA_CMD_DEV_NEW netlink message to attach the VDUSE
> > instance to vDPA.
> >
> > VDUSE devices are stopped as follows:
> >
> > ...
> >
> > > > > + static int netlink_add_vduse(const char *name, int device_id)
> > > > > + {
> > > > > + struct nl_sock *nlsock;
> > > > > + struct nl_msg *msg;
> > > > > + int famid;
> > > > > +
> > > > > + nlsock = nl_socket_alloc();
> > > > > + if (!nlsock)
> > > > > + return -ENOMEM;
> > > > > +
> > > > > + if (genl_connect(nlsock))
> > > > > + goto free_sock;
> > > > > +
> > > > > + famid = genl_ctrl_resolve(nlsock, VDPA_GENL_NAME);
> > > > > + if (famid < 0)
> > > > > + goto close_sock;
> > > > > +
> > > > > + msg = nlmsg_alloc();
> > > > > + if (!msg)
> > > > > + goto close_sock;
> > > > > +
> > > > > + if (!genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, famid, 0, 0,
> > > > > + VDPA_CMD_DEV_NEW, 0))
> > > > > + goto nla_put_failure;
> > > > > +
> > > > > + NLA_PUT_STRING(msg, VDPA_ATTR_DEV_NAME, name);
> > > > > + NLA_PUT_STRING(msg, VDPA_ATTR_MGMTDEV_DEV_NAME, "vduse");
> > > > > + NLA_PUT_U32(msg, VDPA_ATTR_DEV_ID, device_id);
> > > > What are the permission/capability requirements for VDUSE?
> > > >
> > > Now I think we need privileged permission (root user). Because
> > > userspace daemon is able to access avail vring, used vring, descriptor
> > > table in kernel driver directly.
> > Please state this explicitly at the start of the document. Existing
> > interfaces like FUSE are designed to avoid trusting userspace.
>
>
> There're some subtle difference here. VDUSE present a device to kernel which
> means IOMMU is probably the only thing to prevent a malicous device.
>
>
> > Therefore
> > people might think the same is the case here. It's critical that people
> > are aware of this before deploying VDUSE with virtio-vdpa.
> >
> > We should probably pause here and think about whether it's possible to
> > avoid trusting userspace. Even if it takes some effort and costs some
> > performance it would probably be worthwhile.
>
>
> Since the bounce buffer is used the only attack surface is the coherent
> area, if we want to enforce stronger isolation we need to use shadow
> virtqueue (which is proposed in earlier version by me) in this case. But I'm
> not sure it's worth to do that.
The security situation needs to be clear before merging this feature.
I think the IOMMU and vring can be made secure. What is more concerning
is the kernel code that runs on top: VIRTIO device drivers, network
stack, file systems, etc. They trust devices to an extent.
Since virtio-vdpa is a big reason for doing VDUSE in the first place I
don't think it makes sense to disable virtio-vdpa with VDUSE. A solution
is needed.
I'm going to be offline for a week and don't want to be a bottleneck.
I'll catch up when I'm back.
Stefan
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next prev parent reply other threads:[~2021-04-15 14:38 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-31 8:05 [PATCH v6 00/10] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-03-31 8:05 ` [PATCH v6 01/10] file: Export receive_fd() to modules Xie Yongji
2021-03-31 9:15 ` Christian Brauner
2021-03-31 9:26 ` Dan Carpenter
2021-03-31 9:28 ` Christian Brauner
2021-03-31 11:32 ` Yongji Xie
2021-03-31 12:23 ` Christian Brauner
2021-03-31 13:59 ` Yongji Xie
2021-03-31 14:07 ` Christian Brauner
2021-03-31 14:37 ` Yongji Xie
2021-03-31 8:05 ` [PATCH v6 02/10] eventfd: Increase the recursion depth of eventfd_signal() Xie Yongji
2021-03-31 8:05 ` [PATCH v6 03/10] vhost-vdpa: protect concurrent access to vhost device iotlb Xie Yongji
2021-04-09 16:15 ` Michael S. Tsirkin
2021-04-11 5:36 ` Yongji Xie
2021-04-11 20:48 ` Michael S. Tsirkin
2021-04-12 2:29 ` Yongji Xie
2021-04-12 9:00 ` Michael S. Tsirkin
2021-03-31 8:05 ` [PATCH v6 04/10] vhost-iotlb: Add an opaque pointer for vhost IOTLB Xie Yongji
2021-03-31 8:05 ` [PATCH v6 05/10] vdpa: Add an opaque pointer for vdpa_config_ops.dma_map() Xie Yongji
2021-03-31 8:05 ` [PATCH v6 06/10] vdpa: factor out vhost_vdpa_pa_map() and vhost_vdpa_pa_unmap() Xie Yongji
2021-03-31 8:05 ` [PATCH v6 07/10] vdpa: Support transferring virtual addressing during DMA mapping Xie Yongji
2021-04-08 2:36 ` Jason Wang
2021-03-31 8:05 ` [PATCH v6 08/10] vduse: Implement an MMU-based IOMMU driver Xie Yongji
2021-04-08 3:25 ` Jason Wang
2021-04-08 5:27 ` Yongji Xie
2021-03-31 8:05 ` [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-04-08 6:57 ` Jason Wang
2021-04-08 9:36 ` Yongji Xie
2021-04-09 5:36 ` Jason Wang
2021-04-09 8:02 ` Yongji Xie
2021-04-12 7:16 ` Jason Wang
2021-04-12 8:02 ` Yongji Xie
2021-04-12 9:37 ` Jason Wang
2021-04-12 9:59 ` Yongji Xie
2021-04-13 3:35 ` Jason Wang
2021-04-13 4:28 ` Yongji Xie
2021-04-14 8:18 ` Jason Wang
2021-04-16 3:24 ` Jason Wang
2021-04-16 8:43 ` Yongji Xie
2021-03-31 8:05 ` [PATCH v6 10/10] Documentation: Add documentation for VDUSE Xie Yongji
2021-04-08 7:18 ` Jason Wang
2021-04-08 8:09 ` Yongji Xie
2021-04-14 14:14 ` Stefan Hajnoczi
2021-04-15 5:38 ` Yongji Xie
2021-04-15 7:19 ` Stefan Hajnoczi
2021-04-15 8:33 ` Yongji Xie
2021-04-15 14:17 ` Stefan Hajnoczi
2021-04-15 8:36 ` Jason Wang
2021-04-15 9:04 ` Jason Wang
2021-04-15 11:17 ` Yongji Xie
2021-04-16 2:20 ` Jason Wang
2021-04-16 2:58 ` Yongji Xie
2021-04-16 3:02 ` Jason Wang
2021-04-16 3:18 ` Yongji Xie
2021-04-15 14:38 ` Stefan Hajnoczi [this message]
2021-04-16 2:23 ` Jason Wang
2021-04-16 3:19 ` Yongji Xie
2021-04-16 5:39 ` Jason Wang
2021-04-16 3:13 ` Yongji Xie
2021-04-14 7:34 ` [PATCH v6 00/10] Introduce VDUSE - vDPA Device in Userspace Michael S. Tsirkin
2021-04-14 7:49 ` Jason Wang
2021-04-14 7:54 ` Yongji Xie
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