AMD to fix slippery hypervisor-busting bug in its CPU microcode

Patch for Piledriver chips emitted this week to kill off potentially exploitable glitches

Analysis AMD will tomorrow release new processor microcode to crush an esoteric bug that can be potentially exploited by virtual machine guests to hijack host servers.

Machines using AMD Piledriver CPUs, such as the Opteron 6300 family of server chips, and specifically CPU microcode versions 0x6000832 and 0x6000836 – the latest available – are vulnerable to the flaw.

When triggered, the bug can glitch a processor core to execute data as software, which crashes the currently running process. It is possible for a non-root user in a virtual machine to exploit this defect to upset the host system, or trick the host kernel into executing malicious code controlled by the user.

In other words, it is possible on some AMD-powered servers for a normal user in a guest virtual machine to escape to the underlying host and take over the whole shared server. Although it is rather tricky to exploit – for one thing, it requires precise timing – AMD has a fix ready for operating system makers to distribute to affected users from this Monday.