To be able to investigate and work on the the measured boot features I have switched from grub to systemd-boot (sd-boot).
This initial step is optional, but it is useful because this way
/etc/kernel/cmdline will become the new place where the kernel command line can be configured:
. /etc/default/grub echo "root=/dev/mapper/root $GRUB_CMDLINE_LINUX $GRUB_CMDLINE_LINUX_DEFAULT" > /etc/kernel/cmdline
Do not forget to set the correct root file system there, because initramfs-tools does not support discovering it at boot time using the Discoverable Partitions Specification.
The installation has been automated since systemd version 252.6-1, so installing the package has the effect of installing sd-boot in the ESP, enabling it in the UEFI boot sequence and then creating boot loader entries for the kernels already installed on the system:
apt install systemd-boot
If needed, it could be manually installed again just by running
I like to show the boot menu by default, at least until I will be more familiar with sd-boot:
bootctl set-timeout 4
Since other UEFI binaries can be easily chainloaded, I am also going to keep around grub for a while, just to be sure:
cat <<END > /boot/efi/loader/entries/grub.conf title Grub linux /EFI/debian/grubx64.efi END
At this point sd-boot works, but I still had to enable secure boot. So far sd-boot has not been signed with a Debian key known to the shim bootloader, so I needed to create a Machine Owner Key (MOK), enroll it in UEFI and then use it to sign everything.
I dislike the complexity of mokutil and the other related programs, so after removing it and the boot shim I have decided to use sbctl instead. With it I easily created new keys, enrolled them in the EFI key store and then signed everything:
sbctl create-keys sbctl enroll-keys for file in /boot/efi/*/*/linux /boot/efi/EFI/*/*.efi; do sbctl sign -s $file done
Since there is no sbctl package yet I need to make sure that also the kernels installed in the future will be automatically signed, so I have created a trivial script in
/etc/kernel/install.d/ which automatically runs
sbctl sign -s or
Since I am not using the boot shim, I also had to set
/etc/fwupd/uefi_capsule.conf to make firmware updates work automatically.
As a bonus, I have also added to the boot menu the excellent Debian-based GRML live distribution. Since sd-boot is not capable of loopback-mounting CD-ROM images like grub, I first had to extract the kernel and initramfs and copy them to the ESP:
mount -o loop /boot/grml/grml64-full_2022.11.iso /mnt/ mkdir /boot/efi/grml/ cp /mnt/boot/grml64full/* /boot/efi/grml/ umount /mnt/ cat <<END > /boot/efi/loader/entries/grml.conf title GRML linux /grml/vmlinuz initrd /grml/initrd.img options boot=live bootid=grml64full202211 findiso=/grml/grml64-full_2022.11.iso live-media-path=/live/grml64-full net.ifnames=0 END
As expected, after a reboot
bootctl reports the new security features:
System: Firmware: UEFI 2.70 (Lenovo 0.4496) Firmware Arch: x64 Secure Boot: enabled (user) TPM2 Support: yes Boot into FW: supported Current Boot Loader: Product: systemd-boot 252.5-2 Features: ✓ Boot counting ✓ Menu timeout control ✓ One-shot menu timeout control ✓ Default entry control ✓ One-shot entry control ✓ Support for XBOOTLDR partition ✓ Support for passing random seed to OS ✓ Load drop-in drivers ✓ Support Type #1 sort-key field ✓ Support @saved pseudo-entry ✓ Support Type #1 devicetree field ✓ Boot loader sets ESP information ESP: /dev/disk/by-partuuid/1b767f8e-70fa-5a48-b444-cfe5c272d66e File: └─/EFI/systemd/systemd-bootx64.efi ...