The XNU kernel is the basis of Apple's operating systems. Although labeled as a hybrid kernel, it is found to generally operate in a monolithic manner by defining a single privileged trust zone in which all system functionality resides. This has security implications, as a kernel compromise has immediate and significant effects on the entire system. Over the past few years, Apple has taken steps towards a more compartmentalized kernel architecture and a more microkernel-like design. To date, there has been no scientific discussion of SPTM and related security mechanisms. Therefore, the understanding of the system and the underlying security mechanisms is minimal. In this paper, we provide a comprehensive analysis of new security mechanisms and their interplay, and create the first conclusive writeup considering all current mitigations.
