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.
Red Hat would like to thank the Xen project for reporting this issue.
Created xen tracking bugs for this issue
Affects: fedora-all [bug 910914]
This issue did affect the versions of the kernel-xen package as shipped with Red Hat Enterprise Linux 5.
This issue did not affect Red Hat Enterprise Linux 6 and Red Hat Enterprise MRG 2.
xen-4.1.4-4.fc17 has been pushed to the Fedora 17 stable repository. If problems still persist, please make note of it in this bug report.
xen-4.2.1-7.fc18 has been pushed to the Fedora 18 stable repository. If problems still persist, please make note of it in this bug report.
This issue has been addressed in following products:
Red Hat Enterprise Linux 5
Via RHSA-2013:0847 https://rhn.redhat.com/errata/RHSA-2013-0847.html