On Mon, Aug 23, 2021 at 5:38 PM Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote: > > > On 8/23/2021 12:27 PM, Yongji Xie wrote: > > On Mon, Aug 23, 2021 at 5:04 PM Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote: > >> > >> On 8/23/2021 11:35 AM, Yongji Xie wrote: > >>> On Mon, Aug 23, 2021 at 4:07 PM Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote: > >>>> On 8/23/2021 7:31 AM, Yongji Xie wrote: > >>>>> On Mon, Aug 23, 2021 at 7:17 AM Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote: > >>>>>> On 8/9/2021 1:16 PM, Xie Yongji wrote: > >>>>>>> An untrusted device might presents an invalid block size > >>>>>>> in configuration space. This tries to add validation for it > >>>>>>> in the validate callback and clear the VIRTIO_BLK_F_BLK_SIZE > >>>>>>> feature bit if the value is out of the supported range. > >>>>>> This is not clear to me. What is untrusted device ? is it a buggy device ? > >>>>>> > >>>>> A buggy device, the devices in an encrypted VM, or a userspace device > >>>>> created by VDUSE [1]. > >>>>> > >>>>> [1] https://lore.kernel.org/kvm/20210818120642.165-1-xieyongji@xxxxxxxxxxxxx/ > >>>> if it's a userspace device, why don't you fix its control path code > >>>> instead of adding workarounds in the kernel driver ? > >>>> > >>> VDUSE kernel module would not touch (be aware of) the device specific > >>> configuration space. It should be more reasonable to fix it in the > >>> device driver. There is also some existing interface (.validate()) for > >>> doing that. > >> who is emulating the device configuration space ? > >> > > A userspace daemon will initialize the device configuration space and > > pass the contents to the VDUSE kernel module. The VDUSE kernel module > > will handle the access of the config space from the virtio device > > driver, but it doesn't need to know the contents (although we can know > > that). > > So you add a workaround in the guest kernel drivers instead of checking > these quirks in the hypervisor ? > I didn't see any problem adding this validation in the device driver. > VDUSE kernel should enforce the security for the devices it > emulates/presents to the VM. > I agree that the VDUSE kernel should enforce the security for the emulated devices. But I still think the virtio device driver should handle this case since nobody can make sure the device can always set the correct value. Adding this validation would be helpful. > >>> And regardless of userspace device, we still need to fix it for other cases. > >> which cases ? Do you know that there is a buggy HW we need to workaround ? > >> > > No, there isn't now. But this could be a potential attack surface if > > the host doesn't trust the device. > > If the host doesn't trust a device, why it continues using it ? > IIUC this is the case for the encrypted VMs. > Do you suggest we do these workarounds in all device drivers in the kernel ? > Isn't it the driver's job to validate some unreasonable configuration? Thanks, Yongji
