On Fri, 6 Mar 2020 11:35:21 +0800 Jason Wang <jasowang@xxxxxxxxxx> wrote: > On 2020/3/6 上午1:14, Alex Williamson wrote: > > On Tue, 25 Feb 2020 14:09:07 +0800 > > Jason Wang <jasowang@xxxxxxxxxx> 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, 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 > >
