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Hardware Virtualization: Off By Default

Thursday, May 10, 2007

I noticed my x60 tablet had “Intel Virtualization Technology” off by default in the bios. In talking to people and reading blogs, a lot of manufacturers configure their machines similarly.

Turning on VT Technology enables “Hardware Assisted Virtualization” in Virtual PC, which gives virtual machines a performance boost. See Scott Hanselman’s “Virtual PC Tips and Hardware Assisted Virtualization” for more details.

It’s a simple job to enable VT Technology in the BIOS, but I started wondering why every machine seems to have this feature turned off. “Off by default” is a security mantra, and it turns out hardware virtualization extensions do open a potential risk.

The slide deck "Hardware Virtualization Rootkits" (PDF) is an interesting read. It seems a rootkit could use VT Technology to run at a higher privilege level than the operating system itself! Microsoft recommends that manufactures turn the feature off by default for non-server class machines. See: “CPU Virtualization Extensions: Analysis of Rootkit Issues”.

Just more proof that you can’t ship any kind of feature these days without thinking of the security implications.