Microprocessor having a secure execution mode with provisions for monitoring, indicating, and managing security levels

• US 8,819,839 B2
• Filed: 10/31/2008
• Issued: 08/26/2014
• Est. Priority Date: 05/24/2008
• Status: Active Grant

• Current Assignee: VIA Technologies Incorporated (VIA Technologies)
• Original Assignee: VIA Technologies Incorporated (VIA Technologies)
• Inventors: Henry, G. Glenn, Parks, Terry
• Primary Examiner(s): Nigh, James D
• Application Number:
  US12/263,250
• Publication Number:
  US 20090293130A1
• Time in Patent Office: 2,125 Days
• Field of Search: 726/26, 713/194
• US Class Current: 726/26
• CPC Class Codes: G06F 21/72 in cryptographic circuits
• CPC Class Codes: G06F 21/74 operating in dual or compartmented mode, i.e. at least one secure mode
• CPC Class Codes: G06F 21/79 in semiconductor storage media, e.g. directly-addressable memories

Abstract

An apparatus including a microprocessor and a secure non-volatile memory. The microprocessor executes non-secure application programs and a secure application program. The non-secure application programs are accessed from a system memory via a system bus, and the secure application program is executed in a secure execution mode. The microprocessor has a watchdog manager that monitors environments of the microprocessor by noting and evaluating data communicated by a plurality of monitors, and that classifies the data to indicate a security level associated with execution of the secure application program, and that directs secure execution mode logic to perform responsive actions in accordance with the security level. The secure non-volatile memory is coupled to the microprocessor via a private bus, and stores the secure application program. The secure application program is encrypted. Transactions over the private bus are isolated from the system bus and corresponding system bus resources within the microprocessor.

Claims

1. An apparatus providing for a secure execution environment, comprising:

a microprocessor, that executes non-secure application programs and a secure application program, wherein said non-secure application programs are accessed from a system memory via a system bus, and wherein said secure application program is executed in a secure execution mode, said microprocessor comprising;

a watchdog manager, that monitors physical and operating environments of said microprocessor by noting and evaluating data communicated by a plurality of monitors, and that classifies said data to indicate a security level associated with execution of said secure application program, and that directs secure execution mode logic within said microprocessor to perform responsive actions in accordance with said security level, wherein said plurality of monitors operates independently of execution of said secure application program; and

a secure non-volatile memory, coupled to said microprocessor via a private bus, that stores said secure application program, wherein said secure application program is encrypted in system memory according to an asymmetric cryptographic algorithm, and wherein, upon enablement of said secure execution mode, said microprocessor encrypts said secure application program according to a symmetric key algorithm and transfers said secure application program to said secure non-volatile memory over said private bus.

2. The apparatus as recited in claim 1, wherein said plurality of monitors comprises:

a processor voltage monitor, that monitors power and bus termination voltages provided to said microprocessor from a system board, wherein low and high limits for said voltages are programmed via a machine specific register within said secure execution mode logic, and wherein excursions from said limits are reported to said watchdog manager.

3. The apparatus as recited in claim 1, wherein said plurality of monitors comprises:

a thermal monitor, that constantly monitors die temperature of said microprocessor, wherein low and high temperature limits for said die temperature are programmed via a machine specific register within said secure execution mode logic, and wherein excursions from said limits are reported to said watchdog manager.

4. The apparatus as recited in claim 1, wherein said plurality of monitors comprises:

a data monitor, that detects cryptographic and configuration errors associated with said secure application program when fetching said secure application program from said secure non-volatile memory, wherein said errors are reported to said watchdog manager.

5. The apparatus as recited in claim 1, wherein said plurality of monitors comprises:

a secure time stamp counter, that counts the number of cycles of a core clock signal during execution of said secure application program, and configured to compare said number of cycles to a value of a normal time stamp counter, and that reports that a ratio is exceeded to said watchdog manager, wherein said ratio is programmed via a machine specific register within said secure execution mode logic.

6. The apparatus as recited in claim 1, wherein said plurality of monitors comprises:

a bus clock monitor, that determines both short term and long term integrity of a system bus clock which is provided to said microprocessor, and configured to report to said watchdog logic if said system bus clock is held flat for an undue number of cycles, and configured to report to said watchdog logic if said system bus clock'"'"'s frequency experiences a gradual frequency variation.

7. The apparatus as recited in claim 6, wherein said bus clock monitor determines clock-to-clock variation of said bus clock, and wherein an unacceptable clock-to-clock variation is reported to said watchdog logic.

8. The apparatus as recited in claim 6, wherein said bus clock monitor comprises:

a frequency reference unit, that generates a frequency reference that is proportional to said system bus clock, wherein a derivative of said system bus clock is compared to said frequency reference to determine frequency variation of said system bus clock.

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

a secure non-volatile memory, that stores a secure application program, wherein said secure application program is encrypted in a system memory according to an asymmetric cryptographic algorithm; and

a microprocessor, coupled to said secure non-volatile memory via a private bus, that executes non-secure application programs and said secure application program, wherein said secure application program is executed in a secure execution mode, and wherein, upon enablement of said secure execution mode, said microprocessor encrypts said secure application program according to a symmetric key algorithm and transfers said secure application program to said secure non-volatile memory over said private bus, said microprocessor comprising;

a watchdog manager, that monitors physical and operating environments of said microprocessor by noting and evaluating data communicated by a plurality of monitors, and configured to classify said data to indicate a security level associated with execution of said secure application program, and that directs secure execution mode logic within said microprocessor to perform responsive actions in accordance with said security level, wherein said plurality of monitors operates independently of execution of said secure application program.

10. The microprocessor apparatus as recited in claim 9, wherein said plurality of monitors comprises:

a processor voltage monitor, that monitors power and bus termination voltages provided to said microprocessor from a system board, wherein low and high limits for said voltages are programmed via a machine specific register within said secure execution mode logic, and wherein excursions from said limits are reported to said watchdog manager.

11. The microprocessor apparatus as recited in claim 9, wherein said plurality of monitors comprises:

a thermal monitor, that constantly monitors die temperature of said microprocessor, wherein low and high temperature limits for said die temperature are programmed via a machine specific register within said secure execution mode logic, and wherein excursions from said limits are reported to said watchdog manager.

12. The microprocessor apparatus as recited in claim 9, wherein said plurality of monitors comprises:

a data monitor, that detects cryptographic and configuration errors associated with said secure application program when fetching said secure application program from said secure non-volatile memory, wherein said errors are reported to said watchdog manager.

13. The microprocessor apparatus as recited in claim 9, wherein said plurality of monitors comprises:

a secure time stamp counter, that counts the number of cycles of a core clock signal during execution of said secure application program, and that compares said number of cycles to a value of a normal time stamp counter, and that reports that a ratio is exceeded to said watchdog manager, wherein said ratio is programmed via a machine specific register within said secure execution mode logic.

14. The microprocessor apparatus as recited in claim 9, wherein said plurality of monitors comprises:

a bus clock monitor, that determines both short term and long term integrity of a system bus clock which is provided to said microprocessor, and configured to report to said watchdog logic if said system bus clock is held flat for an undue number of cycles, and that reports to said watchdog logic if said system bus clock'"'"'s frequency experiences a gradual frequency variation.

15. The microprocessor apparatus as recited in claim 14, wherein said bus clock monitor determines clock-to-clock variation of said bus clock, and wherein an unacceptable clock-to-clock variation is reported to said watchdog logic.

16. The microprocessor apparatus as recited in claim 14, wherein said bus clock monitor comprises:

a frequency reference unit, that generates a frequency reference that is proportional to said system bus clock, wherein a derivative of said system bus clock is compared to said frequency reference to determine frequency variation of said system bus clock.

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

accessing the secure code in a system memory, wherein the secure code is encrypted according to an asymmetric cryptographic algorithm;

providing a secure non-volatile memory for storage of the secure code;

upon enablement of a secure execution mode, encrypting the secure application code according to a symmetric key algorithm and transferring the secure application program to a secure non-volatile memory over a private bus that is coupled between the secure non-volatile memory and a microprocessor, 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;

first monitoring physical and operating environments of the microprocessor by noting and evaluating data communicated by a plurality of monitors, wherein the plurality of monitors operates independently of execution of the secure code;

classifying the data to indicate a security level associated with execution of the secure code; and

performing responsive actions in accordance with the security level.

18. The method as recited in claim 17, wherein said first monitoring comprises:

second monitoring power and bus termination voltages provided to the microprocessor from a system board, wherein low and high limits for the voltages are programmed via a machine specific register within the secure execution mode logic, and wherein excursions from the limits are reported to the watchdog manager.

19. The method as recited in claim 17, wherein said first monitoring comprises:

second monitoring die temperature of the microprocessor, wherein low and high temperature limits for the die temperature are programmed via a machine specific register within the secure execution mode logic, and wherein excursions from the limits are reported to the watchdog manager.

20. The method as recited in claim 17, wherein said first monitoring comprises:

detecting cryptographic and configuration errors associated with the secure application program when fetching the secure application program from the secure non-volatile memory, wherein the errors are reported to the watchdog manager.

21. The method as recited in claim 17, wherein said first monitoring comprises:

counting the number of cycles of a core clock signal during execution of the secure application program, and comparing the number of cycles to a value of a normal time stamp counter, and reporting that a ratio is exceeded to the watchdog manager, wherein the ratio is programmed via a machine specific register within the secure execution mode logic.

22. The method as recited in claim 17, wherein said first monitoring comprises:

determining both short term and long term integrity of a system bus clock which is provided to the microprocessor, and first reporting to the watchdog logic if the system bus clock is held flat for an undue number of cycles, and second reporting to the watchdog logic if the frequency of the system bus clock experiences a gradual frequency variation.

23. The method as recited in claim 22, wherein the bus clock monitor determines clock-to-clock variation of the bus clock, and wherein an unacceptable clock-to-clock variation is reported to the watchdog logic.

24. The method as recited in claim 22, wherein said determining comprises:

generating a frequency reference that is proportional to the system bus clock, wherein a derivative of the system bus clock is compared to the frequency reference to determine frequency variation of the system bus clock.