Intermittent "Synchronous Exception" on arm64

[dann frazier]

[Impact]
EFI-based arm64 systems will sometimes hang during (re-)boot due to a synchronous exception while starting GRUB. This is reproducible on focal systems that use our prebuilt grubaa64.efi.signed image, but may not impact systems that generate their own grubaa64.efi using focal's grub-mkimage.

[Test Case]
Put an arm64 system in a reboot loop. Wait. A system can survive hundreds of reboots before hitting the problem. Currently this has only been reported on Bluefield hardware.

[Fix]
https://git.savannah.gnu.org/cgit/grub.git/commit/?id=c0e647eb0e2bd09315612446cb4d90f7f75cb44c

Since this is in the grub-mkimage tool as built by grub-unsigned, not grub2, it likely only impacts the images grub2-unsigned generates at build time.

[What could go wrong]
This could screw up the section calculations in a different way, possibly causing a similar problem to pop up somewhere else.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Michael Hudson-Doyle (mwhudson)]

Is this only a problem in Focal?

[dann frazier (dannf)]

It impacts older releases as well (was fixed upstream before 2.06)

[Julian Andres Klode (juliank)]

This is only a problem before 2.06 so marking the main Ubuntu task invalid. I don't know if we are looking for another 2.04 upload, I think we need to get the current one done and then push 2.06 everywhere which coincidentally would fix this as well (though it's not in the changelog so needs manual bug closing :D).

[Julian Andres Klode (juliank)]

Marking as fixed for focal and bionic as 2.06 is available there now