CVE-2021-28702

PCI devices with RMRRs not deassigned correctly Certain PCI devices in a
system might be assigned Reserved Memory Regions (specified via Reserved
Memory Region Reporting, “RMRR”). These are typically used for platform
tasks such as legacy USB emulation. If such a device is passed through to a
guest, then on guest shutdown the device is not properly deassigned. The
IOMMU configuration for these devices which are not properly deassigned
ends up pointing to a freed data structure, including the IO Pagetables.
Subsequent DMA or interrupts from the device will have unpredictable
behaviour, ranging from IOMMU faults to memory corruption.

Notes