Messages in this thread | | | Subject | Re: [PATCH v2 0/7] vfio/pci: SR-IOV support | From | Jason Wang <> | Date | Mon, 9 Mar 2020 11:36:46 +0800 |
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On 2020/3/7 上午12:24, Alex Williamson wrote: > On Fri, 6 Mar 2020 11:35:21 +0800 > Jason Wang <jasowang@redhat.com> wrote: > >> 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 > ATS is a security risk regardless of SR-IOV, how does this change it? > Thanks,
My understanding is the ATS only happen for some bugous devices. Some hardware has on-chip IOMMU, this probably means unprivileged userspace PF driver can control the on-chip IOMMU in this case.
Thanks
> > Alex > >>> 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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