AS/400 and descendants have a security model, but they rely at least partially on a trusted runtime code generator (and, transitively, trusted boot). The system

AS/400 and descendants have a security model, but they rely at least partially on a trusted runtime code generator (and, transitively, trusted boot). The systems have HW assist to tag real pointers, but that's mainly for performance reasons. Pointer validity checks are performed in software (or they were until ten years ago), automatically inserted by the bytecode translator. If you subverted the code generator, your malicious code could get a bit further by forging pointers.