June 28, 2007

Undetectable hypervisor rootkit challenge

Filed under: Hacking,Hardware,Rootkit,Security,VM — Nate Lawson @ 10:51 am

I’m starting to get some queries about the challenge Tom, Peter, and I issued to Joanna. In summary, we’ll be giving a talk at Blackhat showing how hypervisor-based rootkits are not invisible and the detector always has the fundamental advantage. Joanna’s work is very nice, but her claim that hypervisor rootkits are “100% undetectable” is simply not true. We want to prove that with code, not just words.

Joanna recently responded. In summary, she agrees to the challenge with the following caveats:

  • We can’t intentionally crash or halt the machine while scanning
  • We can’t consume more than 90% of the CPU for more than a second
  • We need to supply five new laptops, not two
  • We both provide source code to escrow before the challenge and it is released afterwards
  • We pay her $416,000

The first two requirements are easy to agree to. Of course, the rootkit also shouldn’t do either of those or it is trivially detectable by the user.

Five laptops? Sure, ok. The concern is that even a random guess could be right with 50% probability. She is right that we can make guessing a bad strategy by adding more laptops. But we can also do the same by just repeating the test several times. Each time we repeat the challenge, the probability that we’re just getting lucky goes down significantly. After five runs, the chance that we guessed correctly via random guesses is only 3%, the baseline she established for acceptability. But if she wants five laptops instead, that’s fine too.

I don’t have a problem open-sourcing the code afterwards. However, I don’t see why it’s necessary either. We can detect her software without knowing exactly how it’s implemented. That’s the point.

The final requirement is not surprising. She claims she has put four person-months work into the current Blue Pill and it would require twelve more person-months for her to be confident she could win the challenge. Additionally, she has all the experience of developing Blue Pill for the entire previous year.

We’ve put about one person-month into our detector software and have not been paid a cent to work on it. However, we’re confident even this minimal detector can succeed, hence the challenge. Our Blackhat talk will describe the fundamental principles that give the detector the advantage.

If Joanna’s time estimate is correct, it’s about 16 times harder to build a hypervisor rootkit than to detect it. I’d say that supports our findings.

[Edit: corrected the cost calculation from $384,000]

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