Heads
A minimal Linux that runs as a coreboot or LinuxBoot ROM payload
...Heads is not just another Linux distribution – it combines the physical hardening of specific hardware platforms and flash security features with custom coreboot firmware and a Linux boot loader in ROM. This moves the root of trust into the write-protected region of the SPI flash and prevents further software modifications to the bootup code (and on platforms that support it, Bootguard can protect against many hardware attacks as well).