CVE-2019-18424

An issue was discovered in Xen through 4.12.x allowing attackers to gain
host OS privileges via DMA in a situation where an untrusted domain has
access to a physical device. This occurs because passed through PCI devices
may corrupt host memory after deassignment. 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.
An untrusted domain with access to a physical device can DMA into host
memory, leading to privilege escalation. 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.

Notes