On 2021/4/21 7:18, Jason Gunthorpe wrote:
On Tue, Apr 20, 2021 at 04:04:57PM -0600, Alex Williamson wrote:
The migration control registers must be on a different VF from the VF being plugged into a guest and the two VFs have to be in different IOMMU groups to ensure they are isolated from each other.
I think that's a solution, I don't know if it's the only solution.
Maybe, but that approach does offer DMA access for the migration. For instance to implement something that needs a lot of data like migrating a complicated device state, or dirty page tracking or whatver.
This driver seems very simple - it has only 17 state elements - and doesn't use DMA.
Yes，the operating address of this driver is the MMIO address, not the DMA address, but the internal hardware DMA address is used as data for migration.
I can't quite tell, but does this pass the hypervisor BAR into the guest anyhow? That would certainly be an adquate statement that it is safe, assuming someone did a good security analysis.
ways and it's not very interesting. If the user can manipulate device state in order to trigger an exploit of the host-side kernel driver, that's obviously more of a problem.
Well, for instance, we have an implementation of (VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RUNNING) which means the guest CPUs are still running and a hostile guest can be manipulating the device.
But this driver is running code, like vf_qm_state_pre_save() in this state. Looks very suspicious.
One quick attack I can imagine is to use the guest CPU to DOS the migration and permanently block it, eg by causing qm_mb() or other looping functions to fail.
There may be worse things possible, it is a bit hard to tell just from the code.
.. also drivers should not be open coding ARM assembly as in qm_mb_write()
OK, these codes need to be encapsulated and should not be presented in this driver.
.. and also, code can not randomly call pci_get_drvdata() on a struct device it isn't attached to haven't verified the right driver is bound, or locked correctly.
Yes, This call needs to be placed in an encapsulation interface, and access protection needs to be added.
manipulate the BAR size to expose only the operational portion of MMIO to the VM and use the remainder to support migration itself. I'm afraid that just like mdev, the vfio migration uAPI is going to be used as an excuse to create kernel drivers simply to be able to make use of that uAPI.
I thought that is the general direction people had agreed on during the IDXD mdev discussion?
People want the IOCTLs from VFIO to be the single API to program all the VMMs to and to not implement user space drivers..
This actually seems like a great candidate for a userspace driver.
I would like to know we are still settled on this direction as the mlx5 drivers we are working on also have some complicated option to be user space only.
Jason .