For this recitation, you'll be reading Meltdown. Meltdown, along with Spectre, is a security vulnerability that was discovered in 2018 that affected all modern Intel processors at the time.

To help as you read:

• Sections 2 and 3 give a very good overview of the necessary background, and a toy example to help you understand the basic attack. In working through the toy example—and to help you test whether you understand it—you should make sure you understand why the example uses data*4096 rather than, say, just data, or data*2048.
• Sections 4 and 5 extend that toy example, explaining how Meltdown was actually implemented.
• Section 6 evaluates the attack, explaining what systems are vulnerable and how well the attack performs.
  • Another way to test your understanding: Section 6.4 mentions that ARM and AMD CPUs do not appear susceptible to Meltdown, and posit that it could be that the current implementation of Meltdown is too slow. Why does the speed of the Meltdown code matter here?
• Sections 7 and 8 discuss countermeasures, and some of the consequences of Meltdown.

As you read, think about the following:

• Footnote 10, along with the end of Section 1, reference responsible disclosure practices. What ethical responsibility do you think researchers in this area of computer security have? How should they disseminate knowledge about new attacks?
• Meltdown was a big deal when it was discovered. Why do you think that was? Does this change your assumptions about the security of your devices? How big of a concern are attacks such as Meltdown (and Spectre, which is also mentioned in the paper) compared to other security issues?
• This paper describes the details of one rather specific attack. What higher-level lessons about security did you take away from it?

Question for Recitation

Before you come to this recitation, you'll turn in a brief answer to the following questions (really—we don't need more than a sentence or so for each question). Your TA will be in touch about exactly how to turn that in.

Your answers to these questions should be in your own words, not direct quotations from the paper.

• What is the Meltdown attack?
• How does it work?
• Why is this attack possible? (Or an alternative question, why doesn't Intel simply disable out-of-order execution on its processors?)
• Who is impacted by this attack? Are you?

As always, there are multiple correct answers for each of these questions.

Notes

Supplemental notes for this recitation. These, along with our Sunday office hours are intended to help students who had to miss a recitation due to isolation, but they're also a useful resource for preparing for exams.