Worth reading:
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Secure Boot Stack and Machine Identity
Google server machines use a variety of technologies to ensure that they are booting the correct software stack. We use cryptographic signatures over low-level components like the BIOS, bootloader, kernel, and base operating system image. These signatures can be validated during each boot or update. The components are all Google-controlled, built, and hardened. With each new generation of hardware we strive to continually improve security: for example, depending on the generation of server design, we root the trust of the boot chain in either a lockable firmware chip, a microcontroller running Google-written security code, or the above mentioned Google-designed security chip. Each server machine in the data center has its own specific identity that can be tied to the hardware root of trust and the software with which the machine booted. This identity is used to authenticate API calls to and from low-level management services on the machine. Google has authored automated systems to ensure servers run up-to-date versions of their software stacks (including security patches), to detect and diagnose hardware and software problems, and to remove machines from service if necessary.
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https://cloud.google.com/security/security-design/
Firmware Security 