Secure Boot #
These are guides to install your system with your own Secureboot keys and enforce signed Linux kernels.
Some useful tools I wrote for this job:
ansemjo/mkefikeys: generate signing keys
ansemjo/mksignkernels: bundle and sign kernel images
Arch Linux #
My main system is running Arch in this configuration but I haven’t done a writeup for it yet ..
Do a somewhat standard installation on an UEFI system. I used the
Fedora 28 Server netinst image.
During partitioning, make sure to select at least “custom” partitioning and add a seperate EFI system partition in
/boot/efi. Tick the boxes to encrypt your
/ and any
swap partitions you might create. Technically, a seperate
/boot partition is not required with the bundled kernels we are going to use but Anaconda complains otherwise and you will not be able to boot the system after installation. You could probably do all these steps from within a live rescue system but I haven’t tried that route yet.
Required Packages #
You will need to additionally (after a minimal setup) install:
Then clone and install the above two tools:
cd /tmp/... git clone https://github.com/ansemjo/mkefikeys git clone https://github.com/ansemjo/mksignkernels (cd mkefikeys && make -f install.mk install) (cd mksignkernels && make -f install.mk install)
Signing keys #
Create a set of signing keys in
mkdir /etc/efikeys && cd /etc/efikeys mkefikeys certs der
der target is required to output DER-encoded certificates in case you need to install those in your firmware. This is the case for OVMF, i.e. KVM machines. My Thinkpad needs authenticated “efi signature lists” .. generate them with
Copy files required for installation to the unencrypted ESP:
cp /etc/efikeys/*.cer /boot/efi
Installing them in your firmware is out of the scope of this entry.
Do not enable Secureboot yet. We haven’t signed anything yet and your system will fail to boot.
Sign your kernels #
Now we need to sign the kernels. Simply running
mksignkernels will probably fail with a not-so-useful error message because something will be missing. On virtual machines the Intel microcode is usually not useful and thus not present. Add an empty
MICROCODE = line in
Additionally, you’ll want to use the same kernel commandline as is used for your default installation. You can get the commandline of currently running kernel from
# blablabla # ------- custom targets -------- MICROCODE = CMDLINE = whatever_your_default_kernel_uses
Next, we need to create the output directory:
mksignkernels should succeed now. Otherwise check all the prerequisites:
- EFI stub in
- Signing keys in
- Kernel in
- Initramfs in corresponding
Use systemd-boot #
systemd-boot is installed and you are indeed running UEFI, yadda yadda ..
To install it as the default bootloader, simply issue:
To enable the selection prompt uncomment the
/boot/efi/loader/loader.conf. Otherwise it directly boots the default kernel.
Sign your bootloader #
Before you reboot and attempt to enable Secureboot now, you need to sign the bootloader itself:
mksignkernels sign SIGN=/boot/efi/systemd/systemd-bootx64.efi mksignkernels sign SIGN=/boot/efi/BOOT/BOOTX64.EFI
I actually do not know if both are necessary, I just signed both just in case.
When you reboot you should see systemd-boot’s selection prompt instead of GRUB. If that is the case, there should be an option to “Reboot into Firmware Setup”. Do that and enable Secureboot now.
If all went fine you should be able to normally boot your system now. Starting your machine via GRUB should fail though, as neither GRUB nor any of the kernels it tries to boot are signed.
This section is mostly TODO because I still need to write up my current setup. But since I seem to forget which PCRs to use, I’ll write it down:
tpm2-totp reseal -p 0,1,2,3,5,7,8 -P $password