Techniques and architectures to provide high assurance image invocation in a pre-boot environment. These techniques may augment implementations of the Unified Extensible Firmware Interface (UEFI) to invoke UEFI images using Trusted Execution Technology (TXT). This can operate to combine pre-boot secure flows, such as UEFI image invocation, with the secure launch instruction set extensions of TXT. This may entail combination of the UEFI StartImage instruction with the SMX leaf SENTER instruction. This may operate to allow original equipment manufacturer (OEM) firmware as a guard and that uses UEFI and TXT access control logic at the same instance to pass control to the operating system (OS).