Public bug reported: Since systemd 252, systemd-stub does LoadImage/StartImage to executed the kernel in the .linux section.
See origin PR: https://github.com/systemd/systemd/pull/24777 Before, it was using the "EFI handover protocol". Unfortunately kernel handover is now deprecated. Also it was only for x86, and missing some features. So upstream decided to use LoadImage/StartImage. In order to use LoadImage, it needs to be able to prevent signature verification and measurement. Because the .linux section is part of the UKI that is already signed and measured. Do that that, it overrides the functions in security architectural protocols. Security architectural protocols are part of the platform initialization specifications. They are optional in these specifications, and the platform initialization specifications are optional by themselves. So some UEFI firmware will not support systemd-stub. For upstream this is not really an issue. UKIs are still something new that has not been used by many distributions yet. And there is probably not that many firmware that does not support the needed features. However, Ubuntu Core has been shipping UKIs since Ubuntu Core 20. And kernel handover has been in use by users that have firmware that do not support the needed features. The bugs that can be caused are: * If EFI_SECURITY2_ARCH_PROTOCOL is not implemented, there will be a spurious measurement of the .linux section on PCR 4. We have observed this behavior in the wild. * If EFI_SECURITY_ARCH_PROTOCOL is not implemented, this should generate a "security violation" error. This is hypothetical. We have not yet observed this. Ubuntu Core 24 uses systemd-stub with LoadImage/StartImage. That means some users cannot upgrade from Ubuntu Core 22 to Ubuntu Core 24. systemd-stub still has a fallback to handover entry point if the embedded kernel is too old to support the PE/COFF entry point. The kernel from 24.04 does support both LoadImage/StartImage and handover. That means systemd-stub will always use LoadImage, and never the handover. We need to be able to force systemd-stub to use handover for some of our users. Ubuntu Core supports kernel command line changes from the gadget (since we use PCR12 as part of the PCR policies to unseal storage keys, it is safe). So it is easy to pass the information to enable handover that way. So I propose we look for the "signal" there and force handover. Here is my proposed patch: https://gist.github.com/valentindavid/7ab6247c8fe0d3a91d089d201e160ba4 ** Affects: systemd (Ubuntu) Importance: Undecided Status: New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2088069 Title: systemd-stub should provide a way to be forced to use handover To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/2088069/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
