What is TrustZone?
A Trusted Execution Environment (TEE) is a hardware assisted tamperproof secure environment where you can run software that are isolated from the rest of the system, such as Linux and other operating systems. The software for a TEE can be implemented in various ways, the crucial thing is to have hardware support. It could for example be an external co-processor or it could be something directly integrated on the chip. To support the TEE concept, Arm® introduced the TrustZone® technology back in 2003. TrustZone is directly integrated into the processor but also extends throughout the system via the AMBA® AXI™ bus and specific TrustZone System IP blocks. Software needed to have a full TEE environment normally consists of some piece of code running on the non-secure side, such as code running in user space in Linux and a supporting Linux kernel driver. Likewise on the secure side, you need to implement software that are running the Trusted OS.
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