Downfall: gathering other people's data

How it worked

Gather instructions read many memory locations at once. Under certain conditions the CPU forwarded stale contents of an internal vector register buffer to the instruction before checking that they belonged to the current program. The proof of concept stole AES keys from other users on the same core.

The cost

The microcode fix slows workloads that rely heavily on gather instructions. Intel allowed operators to turn the mitigation off — a trade-off every multi-tenant operator has to make deliberately.

Our reading

Analysis — Altumptic's interpretation of the sources below.

• Each new microarchitectural attack has its own performance bill; budget for them.
• Enclaves inherit the CPU's flaws; they are not a separate, safer machine.
• The safest default is the mitigation on, with exceptions documented.

What it means for you

1. Apply Intel microcode updates through firmware or the OS loader.
2. Keep mitigations on for hosts that run untrusted or multi-tenant code.
3. Measure performance after updates instead of disabling mitigations by habit.