On Mon, 9 Mar 2020 11:36:46 +0800 Jason Wang <jasowang@xxxxxxxxxx> wrote: > On 2020/3/7 上午12:24, Alex Williamson wrote: > > 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, > > > 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. Again, how does this relate to SR-IOV? A PF is currently assignable regardless of the support in this series. Thanks, Alex
