How CHERIoT Provides Strong and Usable Isolation Without an MMU

CHERIoT is a RISC-V-based ISA, RTOS, and programmer model co-designed for security in embedded systems, offering an alternative to memory management units (MMUs) for isolation. Instead of page-based MMU protection, it uses CHERI capabilities—fat pointers carrying address, bounds, permissions, and sealing metadata—to let programmers share complex objects safely across compartments without restructuring APIs around pages or RPC serialization. The piece traces the history of memory protection from early mainframes through Mondriaan Memory Protection to CHERI, explains sealing, sentries, static and dynamic software capabilities, and compares CHERIoT's compartment/thread model to MULTICS shared libraries and the Doors mechanism from Spring/Solaris. It closes by discussing what would need to change to scale these ideas to larger, multicore systems, including temporal safety, stack zeroing, and whether MMUs might still be useful purely for translation and copy-on-write.

Source: https://queue.acm.org/doi/10.1145/3831361. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.