1. Hardware Support for Embedded Operating System Security

2. Introduction Pervasive use of embedded systems
Serious security requirements
Software based solutions not suitable for embedded systems
Hardware monitoring as a solution
Dedicated hardware co-located with the main processor
Ensuring the safe behavior of the main processor at run-time
Signaling the main processor upon detecting a deviation

3. Hardware Monitor Concept
Offline analysis of the code
Checking the execution reports at run-time
Alarming the processor upon detecting a deviation

4. Fine Grained Monitoring
Forming a state diagram based on the assembly code
Compressing the values using hashing
Processing the graph in order to realize it as an state machine

5. Challenges Monitoring multiple parallel applications
Following the context switching between the OS and the applications
Monitoring the OS itself

6. System Architecture Main processor Hardware monitor
Crypto co-processor
Describe an overall working of the system

7. Detection and Recovery
Receiving an instruction with an unacceptable hash value
Interrupting the CPU
Closing the misbehaving task and running the next high priority ready task

8. Prototype Implementation
NIOS II processor on Altera DE4 board
Running µC/OS-II operating system
Another NIOS II processor augmented with RSA decryption engine as the cryptographic processor

9. Resource Overhead Available on FPGA NIOS II with no HW monitor
HW monitor and controller
Secure HW monitor loading
LUTs
182,400
2,152
764
2,603
FFs
2,813
922
2,936
Mem. bits
14,625,792
2,199,552
2,580,288
2,074,492
per core
per system

10. Graph Sizes Number of Instructions Number of Graph Entries
Graph Size (bits)
uC/OS-II
22,913
23,625
850,500
basic_math
10,446
11,563
416,268
bitcount
6,731
7,823
281,628
qsort_small
7,113
9,055
325,980
qsort_large
7,302
9,116
328,176

11. Prototype Evaluation Realization of the hardware monitor on DE4 board
Continuous protection of the system during its normal operation
Successful detection of a format string attack
About 35% area overhead
Negligible performance overhead

12. Summary Security in embedded systems is important
We developed a hardware monitor to detect and stop attacks
Practical solution for complex OS based multitask systems
Small area overhead but memory requirement proportional to binary size
No frequency slow down imposed by the added hardware
A real world attack scenario implemented and stopped using the implemented solution
Effective approach to protecting embedded systems from attacks

13. Thank You