Embodiments of an invention for modifying memory permissions in a secure processing environment are disclosed. In one embodiment, a processor includes an instruction unit and an execution unit. The instruction unit is to receive an instruction to modify access permissions for a page in a secure enclave. The execution unit is to execute the instruction. Execution of the instruction includes setting new access permissions in an enclave page cache map entry. Furthermore, the page is immediately accessible from inside the secure enclave according to the new access permissions.