bootkit

bootkit layer

The build of bootkit creates a layer 'bootkit' that has ovmf (kvm firmware), shim, kernel, and initramfs artifacts in an easily available and organized format.

The list of files in a bootkit layer are:

• bootkit/mos/initrd-mos.cpio.gz - The files needed for 'mos' functionality in an initramfs. This is effectively a "mos initrd module" that can be appended to initrd/core.cpio.gz to give mos functionality.

• bootkit/stubby/stubby.efi - A build of stubby. The consumer combines stubby, kernel, initramfs and cmdline to create a UKI.

• bootkit/ovmf/ovmf-code.fd, bootkit/ovmf/ovmf-vars.fd - A build of OVMF code and vars. The vars are empty, they contain no built-in PK, KEK or DB values, and are expected to be customized before use. Vars can be customized via virt-firmware.

• bootkit/initrd/firmware.cpio.gz - This contains early microcode for linux kernel. If used, it should be the first content in an initramfs and should not be compressed. See linux kernel doc for more information.

• bootkit/kernel/version - text file containing 'uname -r' for the kernel.

• bootkit/kernel/boot/vmlinuz - linux kernel for booting.

• bootkit/kernel/modules.squashfs - A squashfs archive of kernel modules. The top level directory in it is the output of uname -r. It can be directly consumed by mounting over /lib/modules.

• bootkit/kernel/initrd-modules.cpio.gz - a cpio archive of kernel modules that are typically used in an initramfs. (modules.squashfs is a strict superset)

• bootkit/shim/shim.efi - a build of shim with no included VENDOR_DB. This needs to be customized by adding a signature list. See (cert-to-efi-sig-list(1) for information on signature list format.

customized layer

Customized layer can be built with make custom KEYSET_D=/path/to/keyset.

A keyset is needed to build the customized layer. the path to a keyset directory in the same format as keys repository must be provided in the KEYSET_D variable.

Certificates from keyset are embedded into the produced artifacts. Private keys from the provided keyset are used to sign the artifacts.

The customized layer build output contains:

• customized/ovmf-code.fd, customized/ovmf-vars.fd - OVMF code and vars. Vars are populated with uefi-db, uefi-pk, uefi-kek.
• customized/shim.efi - A shim that contains in it's DB the certificates for uki-production, uki-tpm, and uki-limited. It is signed with the uefi-pk private key.
• customized/kernel.efi - a Universal Kernel Image. It contains the manifest-ca/cert.pem key at /manifestCA.pem and is signed with uki-production private key.

oci-boot

oci-boot is a tool that can be used to create a bootable iso or disk image from the files in a bootkit.

After building bootkit and building oci-boot, you can do:

$ skopeo copy docker://.../rootfs:name-squashfs oci:/tmp/oci.d:rootfs-squashfs
FIXME: need to soci sign the rootfs

$ ./pkg/oci-boot out.img \
    oci:$PWD/../build-bootkit/oci:bootkit-squashfs \
    oci:/tmp/oci.d:rootfs-squashfs

Build

Things that can be defined during this build:

• KEYSET_D - Make sets this to the user's machine/trust/keys/snakeoil directory. The keyset (snakeoil) can be changed by setting KEYSET variable to make (make KEYSET=myset).
• DOCKER_BASE - this should reference a docker url that has 'ubuntu:jammy' in it ie, setting to 'docker://' (the default) would use the official docker repos.
• UBUNTU_MIRROR - this is a url to a ubuntu package mirror. default value is http://archive.ubuntu.com/ubuntu