On Tue, May 25, 2021 at 2:48 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Tue, May 25, 2021 at 02:40:57PM +0800, Jason Wang wrote: > > > > 在 2021/5/20 下午5:06, Yongji Xie 写道: > > > On Thu, May 20, 2021 at 2:06 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > On Mon, May 17, 2021 at 05:55:01PM +0800, Xie Yongji wrote: > > > > > This series introduces a framework, which can be used to implement > > > > > vDPA Devices in a userspace program. The work consist of two parts: > > > > > control path forwarding and data path offloading. > > > > > > > > > > In the control path, the VDUSE driver will make use of message > > > > > mechnism to forward the config operation from vdpa bus driver > > > > > to userspace. Userspace can use read()/write() to receive/reply > > > > > those control messages. > > > > > > > > > > In the data path, the core is mapping dma buffer into VDUSE > > > > > daemon's address space, which can be implemented in different ways > > > > > depending on the vdpa bus to which the vDPA device is attached. > > > > > > > > > > In virtio-vdpa case, we implements a MMU-based on-chip IOMMU driver with > > > > > bounce-buffering mechanism to achieve that. And in vhost-vdpa case, the dma > > > > > buffer is reside in a userspace memory region which can be shared to the > > > > > VDUSE userspace processs via transferring the shmfd. > > > > > > > > > > The details and our user case is shown below: > > > > > > > > > > ------------------------ ------------------------- ---------------------------------------------- > > > > > | Container | | QEMU(VM) | | VDUSE daemon | > > > > > | --------- | | ------------------- | | ------------------------- ---------------- | > > > > > | |dev/vdx| | | |/dev/vhost-vdpa-x| | | | vDPA device emulation | | block driver | | > > > > > ------------+----------- -----------+------------ -------------+----------------------+--------- > > > > > | | | | > > > > > | | | | > > > > > ------------+---------------------------+----------------------------+----------------------+--------- > > > > > | | block device | | vhost device | | vduse driver | | TCP/IP | | > > > > > | -------+-------- --------+-------- -------+-------- -----+---- | > > > > > | | | | | | > > > > > | ----------+---------- ----------+----------- -------+------- | | > > > > > | | virtio-blk driver | | vhost-vdpa driver | | vdpa device | | | > > > > > | ----------+---------- ----------+----------- -------+------- | | > > > > > | | virtio bus | | | | > > > > > | --------+----+----------- | | | | > > > > > | | | | | | > > > > > | ----------+---------- | | | | > > > > > | | virtio-blk device | | | | | > > > > > | ----------+---------- | | | | > > > > > | | | | | | > > > > > | -----------+----------- | | | | > > > > > | | virtio-vdpa driver | | | | | > > > > > | -----------+----------- | | | | > > > > > | | | | vdpa bus | | > > > > > | -----------+----------------------+---------------------------+------------ | | > > > > > | ---+--- | > > > > > -----------------------------------------------------------------------------------------| NIC |------ > > > > > ---+--- > > > > > | > > > > > ---------+--------- > > > > > | Remote Storages | > > > > > ------------------- > > > > > > > > > > We make use of it to implement a block device connecting to > > > > > our distributed storage, which can be used both in containers and > > > > > VMs. Thus, we can have an unified technology stack in this two cases. > > > > > > > > > > To test it with null-blk: > > > > > > > > > > $ qemu-storage-daemon \ > > > > > --chardev socket,id=charmonitor,path=/tmp/qmp.sock,server,nowait \ > > > > > --monitor chardev=charmonitor \ > > > > > --blockdev driver=host_device,cache.direct=on,aio=native,filename=/dev/nullb0,node-name=disk0 \ > > > > > --export type=vduse-blk,id=test,node-name=disk0,writable=on,name=vduse-null,num-queues=16,queue-size=128 > > > > > > > > > > The qemu-storage-daemon can be found at https://github.com/bytedance/qemu/tree/vduse > > > > > > > > > > To make the userspace VDUSE processes such as qemu-storage-daemon able to > > > > > run unprivileged. We did some works on virtio driver to avoid trusting > > > > > device, including: > > > > > > > > > > - validating the device status: > > > > > > > > > > * https://lore.kernel.org/lkml/20210517093428.670-1-xieyongji@xxxxxxxxxxxxx/ > > > > > > > > > > - validating the used length: > > > > > > > > > > * https://lore.kernel.org/lkml/20210517090836.533-1-xieyongji@xxxxxxxxxxxxx/ > > > > > > > > > > - validating the device config: > > > > > > > > > > * patch 4 ("virtio-blk: Add validation for block size in config space") > > > > > > > > > > - validating the device response: > > > > > > > > > > * patch 5 ("virtio_scsi: Add validation for residual bytes from response") > > > > > > > > > > Since I'm not sure if I missing something during auditing, especially on some > > > > > virtio device drivers that I'm not familiar with, now we only support emualting > > > > > a few vDPA devices by default, including: virtio-net device, virtio-blk device, > > > > > virtio-scsi device and virtio-fs device. This limitation can help to reduce > > > > > security risks. > > > > I suspect there are a lot of assumptions even with these 4. > > > > Just what are the security assumptions and guarantees here? > > > > > > Note that VDUSE is not the only device that may suffer from this, here're > > two others: > > > > 1) Encrypted VM > > Encrypted VMs are generally understood not to be fully > protected from attacks by a malicious hypervisor. For example > a DoS by a hypervisor is currently trivial. Right, but I mainly meant the emulated virtio-net device in the case of an encrypted VM. We should not leak information to the device/hypervisor. > > > 2) Smart NICs > > More or less the same thing. In my opinion, this is more similar to VDUSE. Without an encrypted VM, we trust the hypervisor but not the device so DOS from a device should be eliminated. Thanks > > > > > > > The attack surface from a virtio device is limited with IOMMU enabled. > > > It should be able to avoid security risk if we can validate all data > > > such as config space and used length from device in device driver. > > > > > > > E.g. it seems pretty clear that exposing a malformed FS > > > > to a random kernel config can cause untold mischief. > > > > > > > > Things like virtnet_send_command are also an easy way for > > > > the device to DOS the kernel. > > > > > > I think the virtnet_send_command() needs to use interrupt instead of > > polling. > > > > Thanks > > > > > > > > And before you try to add > > > > an arbitrary timeout there - please don't, > > > > the fix is moving things that must be guaranteed into kernel > > > > and making things that are not guaranteed asynchronous. > > > > Right now there are some things that happen with locks taken, > > > > where if we don't wait for device we lose the ability to report failures > > > > to userspace. E.g. all kind of netlink things are like this. > > > > One can think of a bunch of ways to address this, this > > > > needs to be discussed with the relevant subsystem maintainers. > > > > > > > > > > > > If I were you I would start with one type of device, and as simple one > > > > as possible. > > > > > > > Make sense to me. The virtio-blk device might be a good start. We > > > already have some existing interface like NBD to do similar things. > > > > > > > > > > > > When a sysadmin trusts the userspace process enough, it can relax > > > > > the limitation with a 'allow_unsafe_device_emulation' module parameter. > > > > That's not a great security interface. It's a global module specific knob > > > > that just allows any userspace to emulate anything at all. > > > > Coming up with a reasonable interface isn't going to be easy. > > > > For now maybe just have people patch their kernels if they want to > > > > move fast and break things. > > > > > > > OK. A reasonable interface can be added if we need it in the future. > > > > > > Thanks, > > > Yongji >
