Re: [PATCH v7 00/12] Introduce VDUSE - vDPA Device in Userspace

Jason Wang
2021-05-25T06:41:14Z

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@redhat.com> 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@bytedance.com/
>>>
>>> - validating the used length:
>>>
>>> * https://lore.kernel.org/lkml/20210517090836.533-1-xieyongji@bytedance.com/
>>>
>>> - 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
2) Smart NICs

> 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