Abstract: A system may use memory tagging for side-channel defense, memory safety, and sandboxing to reduce the likelihood of successful attacks. The system may include memory tagging circuitry to address existing and potential hardware and software architectures security vulnerabilities. The memory tagging circuitry may prevent memory pointers from being overwritten, prevent memory pointer manipulation (e.g., by adding values), and increase the granularity of memory tagging to include byte-level tagging in cache. The memory tagging circuitry may sandbox untrusted code by tagging portions of memory to indicate when the tagged portions of memory include contain a protected pointer. The memory tagging circuitry provides security features while enabling CPUs to continue using and benefiting from speculatively performing operations.