passed through PCI devices may corrupt host memory after deassignment

ISSUE DESCRIPTION

When a PCI device is assigned to an untrusted domain, it is possible for that domain to program the device to DMA to an arbitrary address. The IOMMU is used to protect the host from malicious DMA by making sure that the device addresses can only target memory assigned to the guest. However, when the guest domain is torn down, or the device is deassigned, the device is assigned back to dom0, thus allowing any in-flight DMA to potentially target critical host data.

IMPACT

An untrusted domain with access to a physical device can DMA into host memory, leading to privilege escalation.

VULNERABLE SYSTEMS

Only systems where guests are given direct access to physical devices capable of DMA (PCI pass-through) are vulnerable. Systems which do not use PCI pass-through are not vulnerable.