There are several peripherals running their own OS. Those have their access to RAM limited by an iommu and they have no direct access to the primary storage (they may have some local ROM storage for firmware). If you're asking about the other OS that runs on the application processor such as the bootloaders, trusted firmware, trusted os, etc, then no, those have a superset of access to what the primary OS running on those cores have access to. This is by design.