xen: denial of service

[1] The oxenstored daemon (the ocaml version of the xenstore daemon) does not correctly handle unusual or malicious contents in the xenstore ring. A malicious guest can exploit this to cause oxenstored to read past the end of the ring (and very likely crash) or to allocate large amounts of RAM.

A malicious guest administrator can mount a denial of service attack affecting domain control and management functions.

[2] To avoid an erratum in early hardware, the Xen AMD IOMMU code by default chooses to use a single interrupt remapping table for the whole system. This sharing implies that any guest with a passed through PCI device that is bus mastering capable can inject interrupts into other guests, including domain 0.

Furthermore, regardless of whether a shared interrupt remapping table is in use, old entries are not always cleared, providing opportunities (which accumulate over time) for guests to inject interrupts into other guests, again including domain 0.

In a typical Xen system many devices are owned by domain 0 or driver domains, leaving them vulnerable to such an attack. Such a DoS is likely to have an impact on other guests running in the system.

A malicious domain which is given access to a physical PCI device can mount a denial of service attack affecting the whole system.