In this write up, we will focus mainly on the ARMv8-A exceptions, the role of ARM Trusted Firmware (that provides Secure Monitor functionality) and how the World Switch happens between Secure and Normal. If we look on the the architectural diagram of ARM Trustzone w.r.t ARMv8-A, the Execution Level is divided into four levels namely: EL0 (Secure & Non-Secure) - User Application EL1 (Secure & Non-Secure) - Kernel EL2 - Hypervisor for running different OS's simuntaneously EL3 - Security Monitor Now, whenever a normal world User Application calls for some Secure Operation, the calls goes via IOCTL call to the Linux Driver, which ultimately calls the smc instruction. To understand what the smc instruction, we have to look on the Exceptions in ARMv8 ARMv8 Exceptions In ARMv8 the exceptions are divided into two categories: Synchronous & Asynchronous. An exception is described as synchronous if it is generated as a result of execution or attempted executi...