Messages in this thread | | | Subject | Re: [PATCH v5] virtio-blk: Add validation for block size in config space | From | Max Gurtovoy <> | Date | Mon, 23 Aug 2021 12:38:19 +0300 |
| |
On 8/23/2021 12:27 PM, Yongji Xie wrote: > On Mon, Aug 23, 2021 at 5:04 PM Max Gurtovoy <mgurtovoy@nvidia.com> wrote: >> >> On 8/23/2021 11:35 AM, Yongji Xie wrote: >>> On Mon, Aug 23, 2021 at 4:07 PM Max Gurtovoy <mgurtovoy@nvidia.com> wrote: >>>> On 8/23/2021 7:31 AM, Yongji Xie wrote: >>>>> On Mon, Aug 23, 2021 at 7:17 AM Max Gurtovoy <mgurtovoy@nvidia.com> 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@bytedance.com/ >>>> 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 ?
VDUSE kernel should enforce the security for the devices it emulates/presents to the VM.
> >>> 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 ?
Do you suggest we do these workarounds in all device drivers in the kernel ?
> > Thanks, > Yongji
| |