Messages in this thread | | | Subject | Re: [PATCH v2 0/7] vfio/pci: SR-IOV support | From | Jason Wang <> | Date | Fri, 6 Mar 2020 11:35:21 +0800 |
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On 2020/3/6 上午1:14, Alex Williamson wrote: > On Tue, 25 Feb 2020 14:09:07 +0800 > Jason Wang <jasowang@redhat.com> wrote: > >> On 2020/2/25 上午10:33, Tian, Kevin wrote: >>>> From: Alex Williamson >>>> Sent: Thursday, February 20, 2020 2:54 AM >>>> >>>> Changes since v1 are primarily to patch 3/7 where the commit log is >>>> rewritten, along with option parsing and failure logging based on >>>> upstream discussions. The primary user visible difference is that >>>> option parsing is now much more strict. If a vf_token option is >>>> provided that cannot be used, we generate an error. As a result of >>>> this, opening a PF with a vf_token option will serve as a mechanism of >>>> setting the vf_token. This seems like a more user friendly API than >>>> the alternative of sometimes requiring the option (VFs in use) and >>>> sometimes rejecting it, and upholds our desire that the option is >>>> always either used or rejected. >>>> >>>> This also means that the VFIO_DEVICE_FEATURE ioctl is not the only >>>> means of setting the VF token, which might call into question whether >>>> we absolutely need this new ioctl. Currently I'm keeping it because I >>>> can imagine use cases, for example if a hypervisor were to support >>>> SR-IOV, the PF device might be opened without consideration for a VF >>>> token and we'd require the hypservisor to close and re-open the PF in >>>> order to set a known VF token, which is impractical. >>>> >>>> Series overview (same as provided with v1): >>> Thanks for doing this! >>> >>>> The synopsis of this series is that we have an ongoing desire to drive >>>> PCIe SR-IOV PFs from userspace with VFIO. There's an immediate need >>>> for this with DPDK drivers and potentially interesting future use >>> Can you provide a link to the DPDK discussion? >>> >>>> cases in virtualization. We've been reluctant to add this support >>>> previously due to the dependency and trust relationship between the >>>> VF device and PF driver. Minimally the PF driver can induce a denial >>>> of service to the VF, but depending on the specific implementation, >>>> the PF driver might also be responsible for moving data between VFs >>>> or have direct access to the state of the VF, including data or state >>>> otherwise private to the VF or VF driver. >>> Just a loud thinking. While the motivation of VF token sounds reasonable >>> to me, I'm curious why the same concern is not raised in other usages. >>> For example, there is no such design in virtio framework, where the >>> virtio device could also be restarted, putting in separate process (vhost-user), >>> and even in separate VM (virtio-vhost-user), etc. >> >> AFAIK, the restart could only be triggered by either VM or qemu. But >> yes, the datapath could be offloaded. >> >> But I'm not sure introducing another dedicated mechanism is better than >> using the exist generic POSIX mechanism to make sure the connection >> (AF_UINX) is secure. >> >> >>> Of course the para- >>> virtualized attribute of virtio implies some degree of trust, but as you >>> mentioned many SR-IOV implementations support VF->PF communication >>> which also implies some level of trust. It's perfectly fine if VFIO just tries >>> to do better than other sub-systems, but knowing how other people >>> tackle the similar problem may make the whole picture clearer. 😊 >>> >>> +Jason. >> >> I'm not quite sure e.g allowing userspace PF driver with kernel VF >> driver would not break the assumption of kernel security model. At least >> we should forbid a unprivileged PF driver running in userspace. > It might be useful to have your opinion on this series, because that's > exactly what we're trying to do here. Various environments, DPDK > specifically, want a userspace PF driver. This series takes steps to > mitigate the risk of having such a driver, such as requiring this VF > token interface to extend the VFIO interface and validate participation > around a PF that is not considered trusted by the kernel.
I may miss something. But what happens if:
- PF driver is running by unprivileged user - PF is programmed to send translated DMA request - Then unprivileged user can mangle the kernel data
> We also set > a driver_override to try to make sure no host kernel driver can > automatically bind to a VF of a user owned PF, only vfio-pci, but we > don't prevent the admin from creating configurations where the VFs are > used by other host kernel drivers. > > I think the question Kevin is inquiring about is whether virtio devices > are susceptible to the type of collaborative, shared key environment > we're creating here. For example, can a VM or qemu have access to > reset a virtio device in a way that could affect other devices, ex. FLR > on a PF that could interfere with VF operation. Thanks,
Right, but I'm not sure it can be done only via virtio or need support from transport (e.g PCI).
Thanks
> > Alex >
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