MAC for Zephyr was presented at Linux Security Summit (2019), https://www.youtube.com/watch?v=AKWFbxbsU3o

  .. a flexible MAC architecture was created and matured through a series of research systems. The work to bring this architecture to mainstream systems [and] experience with applying this architecture to mobile platforms is examined. The role of MAC in a larger system architecture is reviewed in the context of a secure virtualization system. The state of MAC in mainstream systems is compared before and after our work. 

Review of non-public STM for constraining SMM, https://www.platformsecuritysummit.com/2018/speaker/myers/

  We describe our work to demonstrate an enhanced SMI transfer monitor (STM) to provide protected execution services on the x86 platform. An STM is a hypervisor that executes in x86 system management mode (SMM) and functions as a peer to the hypervisor or operating system. The STM constrains the SMI handler, by hosting the handler in a virtual machine (VM). Otherwise, the SMI handler holds unconstrained access to the platform, which could undermine the assurance provided by DRTM or TXT.

OSS STM contributed to coreboot, https://cyberscoop.com/nsa-firmware-open-source-coreboot-stm... & https://www.osfc.io/2019/talks/implementing-stm-support-for-...

  Implementation of SMI transfer monitor (STM) support for Coreboot.