Messages in this thread | | | Subject | Re: [PATCH v7 00/12] Introduce VDUSE - vDPA Device in Userspace | From | Jason Wang <> | Date | Tue, 25 May 2021 14:40:57 +0800 |
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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
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