This bug was fixed in the package systemd - 255.4-1ubuntu8.6
---------------
systemd (255.4-1ubuntu8.6) noble; urgency=medium
* stub: add magic cmdline option to force EFI handover
(LP: #2088069)
* localed: use ubuntu core hack for locale.conf and vconsole.conf
(LP: #2091657)
-- Nick Rosbrook <en...@ubuntu.com> Fri, 21 Feb 2025 16:18:31 -0500
** Changed in: systemd (Ubuntu Noble)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/2088069
Title:
systemd-stub should provide a way to be forced to use handover
Status in systemd package in Ubuntu:
Won't Fix
Status in systemd source package in Noble:
Fix Released
Status in systemd source package in Oracular:
Won't Fix
Bug description:
[Original description/Impact]
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
[Test plan]
Unfortunately, because of the way the pc-kernel snap is built, we
cannot trivially test changes once they land in -proposed. In order to
test this ahead of time, we applied this patch in a PPA[1], and then
rebuilt the kernel snap in a private PPA such that we could deploy
something testable to the affected customer.
To get a full end-to-end test, we need to release the fix to -updates
first so that a genuine pc-kernel snap can be built and tested by the
customer.
[1] https://launchpad.net/~enr0n/+archive/ubuntu/systemd-stub-force-
handover
[Where problems could occur]
This patch adds logic to systemd-stub to obey a magic kernel command
line. It is limited to systemd-stub, which currently is only used in
Ubuntu core, so this should not have any impact on classic systems
whatsoever.
By default, when the command line option is not set, no behavior
should change. However, if there are problems with the command line
parsing that would potentially cause problems for Ubuntu core users.
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