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README |
Currently, only one implementation of Secure Boot is available out of the box, which is using a single signed EFI application to directly boot the kernel with an optional initramfs. This can be added to your build either through local.conf, or via your own custom image recipe. If you are adding it via local.conf, set the following variables: IMAGE_FEATURES += "secureboot" WKS_FILE = "generic-bootdisk.wks.in" SECURE_BOOT_SIGNING_KEY = "/path/to/your/signing/key" SECURE_BOOT_SIGNING_CERT = "/path/to/your/signing/cert" IMAGE_CLASSES += "uefi-comboapp" If working with an image recipe, you can inherit uefi-comboapp directly instead of using the IMAGE_CLASSES variable. The signing keys and certs can be created via openssl commands. Here's an example: openssl req -new -x509 -newkey rsa:2048 -subj "/CN=your-subject/" -keyout \ your-key.key -out your-key.crt -days 365 -nodes -sha256 openssl x509 -in your-key.crt -out your-key.cer -outform DER The .crt file is your SECURE_BOOT_SIGNING_CERT, and the .key file is your SECURE_BOOT_SIGNING_KEY. You should enroll the .crt key in your firmware under the PK, KEK, and DB options (methods are different depending on your firmware). If a key should ever become invalid, enroll it under DBX to blacklist it. The comboapp can be further manipulated in a number of ways. You can modify the kernel command line via the APPEND variable, you can change the default UUID via the DISK_SIGNATURE_UUID variable, and you can modify the contents of the initramfs via the INITRD_IMAGE or INITRD_LIVE variables. A simple Secure Boot enabled image used for testing can be viewed at: common/recipes-selftest/images/secureboot-selftest-image-signed.bb