OpenHours Bootloaders and Secure Firmware
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The document discusses bootloaders and trusted firmware, focusing on the differences between Cortex A and Cortex M processors. It emphasizes the importance of establishing a root of trust through a chain of executed code to ensure secure operation. Additionally, it details the structure and responsibilities of various bootloader stages for both types of processors.
OpenHours Bootloaders and Secure Firmware
- 1. Bootloaders and Trusted Firmware David Brown 2019 April 24
- 2. Overview ● Signature introduction ● Two worlds: Cortex A and Cortex M ● Trusting your code: The root of trust ● Secure vs Non-secure ● Bootloaders, trusted firmware, and secure code, oh my
- 3. A Digital Signature Image SHA256 Image Hash 32 bytes EC Private Key ECDSA Sign Signature 32 bytes
- 4. Verify a Signature Image SHA256 Image Hash 32 bytes EC Public Key ECDSA Verify Signature 32 bytes Good?
- 5. Cortex A vs Cortex M Cortex A: ● “Big” CPUs ● Typically have: ○ GBs of RAM ○ GBs of storage: SSD/MMC/NAND ○ GHz CPU ○ Multiple cores common ● Think Raspberry Pi, Phones, 96Boards, Android, Linux, etc Cortex M: ● “Small” CPUs ● Typically have: ○ KBs of RAM ○ MBs of ROM ○ 10-100s of MHz ○ Usually 1 core, some 2 ● Think IoT: light bulbs, water meters ● Key here is to reduce cost and power consumption
- 6. Root of trust ● How do we trust the code that is running? ● Chain of trust from first executed code on the system
- 7. Chain of Trust Internal boot code Bootloader Trusted Firmware Non-secure Operating System Trusted OS Application Secure Non-Secure Optional
- 8. Internal boot code Bootloader Trusted Firmware Non-secure Operating System Trusted OS Application Secure Non-secure
- 9. Secure, Non-secure Interaction ● Strong memory protection ● Memory protection even of DMA ● Well defined and restricted communication ● Limits code that needs to be trusted
- 10. Bootloaders, Cortex-A ● Code resides in file or partition in a large device ● Each stage responsible for verifying the next state ○ BL1: Rom loader in SoC ○ BL2: Trusted firmware ○ BL3-1: Trusted OS/Platform ○ BL3-3: Non-trusted: U-Boot/UEFI ○ : Non-secure OS: Linux ○ : Apps
- 11. Bootloaders: Cortex-M ● Lives in a single flash space ● May execute right out of flash ● Fixed partitions and rigid upgrades ● Boot order: ○ Possible on-SoC init ROM ○ MCUboot: Validates 2 images ○ TF-M: Secure application ○ Application
- 12. Thank you Join Linaro to accelerate deployment of your Arm- based solutions through collaboration contact@linaro.org