UEFI Secure Boot is an important feature that secures the root of trust. When configured correctly, it ensures that your kernel boots the way that you want, without malicious modifications. In coreboot, it's made possible by the SMMSTORE feature.

But there's a problem: SMMSTORE was developed for basic functionality, not security. This talk is about the security vulnerability in the coreboot implementation of Secure Boot that's caused by decoupling implementation-level details, like verification, from performing the SPI write in coreboot, and how we fixed it by allowing part of UEFI into SMM to make this atomic again.