Securing the EDK II Image Loader

Abstract: The Unified Extensible Firmware Interface (UEFI) is a standardised interface between the firmware and the operating system used in all x86-based platforms over the past ten years, which continues to spread to other architectures such as ARM and RISC-V. The UEFI incorporates a modular design based on images containing a driver or an application in a Common Object File Format (COFF) either as a Portable Executable (PE) or as a Terse Executable (TE). The de-facto standard generic UEFI services implementation, including the image loading functionality, is TianoCore EDK II. Its track of security issues shows numerous design and implementation flaws some of which are yet to be addressed. In this paper we outline both the requirements for a secure UEFI Image Loader and the issues of the existing implementation. As an alternative we propose a formally verified Image Loader supporting both PE and TE images with fine-grained hardening enabling a seamless integration with EDK II and subsequently with the other firmwares.