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Verified Boot on Chrome OS and How to do it yourself

Abstract

Chrome OS uses a first stage read-only firmware and second-stage updatable firmware. The updatable firmware is signed and contains kernel keys and a dm-verify hash, so that the firmware, Linux kernel and root filesystem are all protected against corruption and attack. This system is described and discussed. As part of Google's upstream efforts in U-Boot, a generalized secure boot system has been developed and released with U-Boot 2013.07. This implementation uses the FIT format, which collects together images, such as kernels, device tree, RAM disks. Support is provided for TPMs (Trust Platform Module), RSA-based signing and verificaiton, and hashing with hardware acceleration. This system is also described and discussed, along with the specific steps needed to implement it in your designs.