This document represents a proposed Change. As part of the Changes
process, proposals are publicly announced in order to receive
community feedback. This proposal will only be implemented if approved
by the Fedora Engineering Steering Committee.
== Summary ==
Add support for unified kernels images to Fedora.
== Owner ==
* Name: [[User:kraxel| Gerd Hoffmann]]
* Email: kraxel(a)redhat.com
== Detailed Description ==
The goal is to move away from initrd images being generated on the
installed machine. They are generated while building the kernel
package instead, then shipped as part of a unified kernel image.
A unified kernel image is an all-in-one efi binary containing kernel,
initrd, cmdline and signature. The secure boot signature covers
everything, specifically the initrd is included which is not the case
when the initrd gets loaded as separate file from /boot.
Main motivation for this move is to make the distro more robust and more secure.
Switching the whole distro over to unified kernels quickly is not
realistic though. Too many features are depending on the current
workflow with a host-specific initrd (and host-specific kernel command
line), which is fundamentally incompatible with unified kernels where
everybody will have the same initrd and command line. Thats why there
is 'Phase 1' in title, so we can have more Phases in future releases
A host-specific initrd / command line is needed today for:
* features needing optional dracut modules (initrd rebuild needed to
* configuration / secrets baked into the initrd (booting from iscsi
* configuration being specified on the kernel command line.
** root filesystem being the most important one.
allow to remove this.
Phase 1 goals (high priority):
* Ship a unified kernel image as (optional) kernel sub-rpm. Users can
opt-in to use that kernel by installing the sub-rpm. Initial focus is
on booting virtual machines where we have a relatively small and well
defined set of drivers / features needed. Supporting modern physical
machines with standard setup (i.e. boot from local sata/nvme storage)
too should be easy.
* Update kernel install scripts so unified kernels are installed and
* Add bootloader support for unified kernel images. Add
unified kernel bls support] to grub2, or support using systemd-boot,
Phase 1 goals (lower priority, might move to Phase 2):
* Add proper discoverable partitions support to installers (anaconda,
image builder, ...).
** Temporary workaround possible: set types using sfdisk in %post script.
** When using btrfs: configure 'root' subvolume as default volume.
* Add proper systemd-boot support to installers.
** Temporary workaround possible: run 'bootctl install' in %post script.
* Better measurement and remote attestation support.
** store kernel + initrd hashes somewhere (kernel-hashes.rpm ?) to
allow pre-calculate TPM PCR values.
** avoid using grub2 (measures every config file line executed which
is next to impossible to pre-calculate).
* Switch cloud images to use unified kernels.
Phase 2/3 goals (longer-term stuff which is not realistic to complete for F38).
* Move away from using the kernel command line for configuration.
* Move away from storing secrets in the initrd.
* Handle dracut optional modules in a different way.
systemd has some building blocks which can be used, although none of
them are used by fedora today.
systemd credentials] can be used for secrets (also for configuration).
unified kernel stub] can load credentials from the ESP.
The unified kernel stub can also load
extensions] from the ESP, which can possibly be used to replace
optional dracut modules.
== Feedback ==
== Benefit to Fedora ==
* Better secure boot support (specifically the initrd is covered by
* Better confidential computing support (measurements are much more
useful if we know what hashes to expect for the initrd).
* More robust boot process (generating the initrd on the installed
system is fragile, root cause for kernel bugs reported is simply a
broken initrd sometimes).
== Scope ==
* Proposal owners:
** Update kernel build to create unified kernel sub-package.
*** part one: [https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2179
*** part two: (wip)
* Other developers:
** grub2: add unified kernel support
*** wip code at [https://github.com/osteffenrh/grub2/
** installer(s): add support for discoverable partitions.
* Release engineering: [https://pagure.io/releng/issues
#Releng issue number]
* Policies and guidelines: N/A (not needed for this Change)
* Trademark approval: N/A (not needed for this Change)
* Alignment with Objectives:
== Upgrade/compatibility impact ==
None (using unified kernel is opt-in for Phase 1).
== How To Test ==
Try on a existing (uefi) system:
* make sure you are running fedora 37 or rawhide.
* make sure your root filesystem has type "Linux root (x86-64)" (use
`fdisk -l` to check).
** should that not be the case use the fdisk tag command ('t') to
change the partition type.
* when using btrfs: make sure the 'root' subvolume is set as default volume.
* `dnf copr enable kraxel/unified.kernel`
* `dnf update "grub2*"`
* `dnf install kernel-unified-virt`
You should find two entries in the grub2 boot menu, one for classing
kernel with separate initrd and one for the unified kernel image.
Both should boot fine.
project has kickstart files
and helper scripts for generating virtual machine images.
* image using grub2-efi:
* image using systemd-boot:
Prebuilt virtual machine images are available from
== User Experience ==
== Dependencies ==
== Contingency Plan ==
* Contingency mechanism:
** Probably none (unified kernel images are opt-in for Phase 1).
** In case we tried switching the cloud images to unified kernels:
revert the kickstart config changes.
* Contingency deadline:
* Blocks release? No
== Documentation ==
== Release Notes ==
He / Him / His
Fedora Program Manager