Memory protection in embedded systems

• We present a model of a protection system based on passwords, protection contexts and protection domains.
• A protection context is a set of access rights for the memory pages.
• Passwords are associated with protection domains, which are sets of protection contexts.
• At the hardware level, the model is supported by a memory protection unit interposed between the processor and the main memory.

With reference to an embedded system featuring no support for memory management, we present a model of a protection system based on passwords. At the hardware level, our model takes advantage of a memory protection unit (MPU) interposed between the processor and the complex of the main memory and the input-output devices. The MPU supports both concepts of a protection context and a protection domain. A protection context is a set of access rights for the memory pages; a protection domain is a set of one or more protection contexts. Passwords are associated with protection domains. A process that holds a given password can take advantage of this password to activate the corresponding domain. A small set of protection primitives makes it possible to modify the composition of the domains in a strictly controlled fashion.The proposed protection model is evaluated from a number of important viewpoints, which include password distribution, review and revocation, the memory requirements for storage of the information concerning protection, and the time necessary for password validation.

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