Protection of secured boot secrets for operating system reboot

Protecting secured boot secrets while starting an operating system. Embodiments include identifying that a second operating system is to be started to replace a first operating system, and loading code of the second operating system in a protected portion of the system memory. The protected portion of the system memory is then unprotected, and processor state is set to initiate execution of the code of the second operating system, while using one or more secured boot secrets that were stored in the protected portion of the system memory by the first operation system to attest a security status of the second operating system. The portion of the system the memory is re-protected, including preventing access to the portion of the system memory by the second operating system.