Apparatus and method for isolating a secure execution mode in a microprocessor

A microprocessor apparatus, for executing secure code within a secure execution environment, the microprocessor apparatus comprising:

• a secure non-volatile memory, configured to store a secure application program;
• and
• a microprocessor, coupled to said secure non-volatile memory via a private bus, configured to execute non-secure application programs and said secure application program, said microprocessor comprising:
• a bus interface unit, configured to accomplish system bus transactions over a system bus to access said non-secure applications in system memory;
• a secure non-volatile memory interface unit, configured to couple said microprocessor to said secure non-volatile memory via a private bus, wherein private bus transactions over said private bus to access said secure non-volatile memory are hidden from observation by system bus resources within said microprocessor and to any device coupled to said system bus;
• and
• secure execution mode logic, configured to provide for a secure execution mode within said microprocessor for execution of said secure application program, wherein said secure execution mode logic records the state of said microprocessor in a non-volatile indicator register upon entry into said secure execution mode and upon exit from said secure execution mode.

A method for executing secure code within a secure execution environment, the method comprising:

• providing a secure non-volatile memory for storage of the secure code;
• storing the secure code within the secure non-volatile memory via private transactions accomplished over a private bus that is coupled to the secure non-volatile memory;
• entering a secure execution mode within a microprocessor for execution of the secure code, said entering comprising:
• upon entry into the secure execution mode, recording the state of the microprocessor in a non-volatile indicator register;
• fetching the secure code from the secure non-volatile memory over the private bus for execution by a microprocessor;
• and
• within the secure execution mode, executing the secure code;
• wherein the private bus is isolated from all system bus resources within the microprocessor and external to the microprocessor, and wherein the private bus is observable and accessible exclusively by secure execution logic within the microprocessor.