Certain PCI devices in a system might be assigned Reserved Memory Regions (specified via Reserved Memory Region Reporting, RMRR) for Intel VT-d or Unity Mapping ranges for AMD-Vi. These are typically used for platform tasks such as legacy USB emulation.
Since the precise purpose of these regions is unknown, once a device associated with such a region is active, the mappings of these regions need to remain continuouly accessible by the device. In the logic establishing these mappings, error handling was flawed, resulting in such mappings to potentially remain in place when they should have been removed again. Respective guests would then gain access to memory regions which they arent supposed to have access to.
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Xen | Ubuntu | focal | * |
| Xen | Ubuntu | oracular | * |
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.