[Bug 1848892] Re: "error: Unknown TPM error." after upgrading to grub 2.04

[AtesComp]

On a 19.04 system, I don't see the /boot/grub/x86_64-efi/tmp.mod file--
so added during the upgrade.

Speculation:
--------------------
So, the problem might be related to signed versus unsigned kernels.  The earlier kernel was probably signed.  The new kernels from the upgrade are probably not signed.  Can't test right now, but will follow up with another laptop.  I will upgrade to 19.10 in the same way.

Using command:
  dpkg --list | grep linux-image
to list kernels lists past kernels not currently installed.  Example on a 19.04 system:
...
rc  linux-image-5.0.0-20-generic  5.0.0-20.21  amd64  Signed kernel image generic
ic  linux-image-5.0.0-21-generic  5.0.0-21.22  amd64  Signed kernel image generic
ii  linux-image-5.0.0-31-generic  5.0.0-31.33  amd64  Signed kernel image generic
ii  linux-image-5.0.0-32-generic  5.0.0-32.34  amd64  Signed kernel image generic
ii  linux-image-generic           5.0.0.32.33  amd64  Generic Linux kernel image

I only have the -31- and -32- kernels installed as is seen in the /boot/
dir:

-rw-------  1 root root  8785656 Sep 30 13:38 vmlinuz-5.0.0-31-generic
-rw-------  1 root root  8785656 Sep 30 22:58 vmlinuz-5.0.0-32-generic

See possibly related Bug #1788727:
  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1848892

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https://bugs.launchpad.net/bugs/1848892

Title:
  "error: Unknown TPM error." after upgrading to grub 2.04

Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  After upgrading to eoan today (via `do-release-upgrade -d`), my laptop
  failed to boot into the OS. I got the grub 2.04 screen (showing only
  Ubuntu), but selecting that gave me about 20 lines of "error: Unknown
  TPM error.", followed by "error: you need to load the kernel first"
  and no way to proceed/recover. Advanced options didn't work either.
  Dropping into the grub console and writing a simple command like `set
  root=(hd1,gpt5)` failed again with a TPM error. It goes without saying
  that booting had worked before with disco/grub 2.02.

  As a workaround, I eventually managed to boot using an eoan live CD,
  chroot'ed into my system, added the `disco main` repo, and forcefully
  downgraded to disco's 2.02. After reinstalling grub to the efi
  partition, booting finally worked again (with grub 2.02).

  lsb_release -rd
  Description:	Ubuntu 19.10
  Release:	19.10

  apt-cache policy grub-efi
  grub-efi:
    Installed: 2.02+dfsg1-12ubuntu2
    Candidate: 2.04-1ubuntu12
    Version table:
       2.04-1ubuntu12 500
          500 http://ubuntu.inode.at/ubuntu eoan/main amd64 Packages
   *** 2.02+dfsg1-12ubuntu2 500
          500 http://ubuntu.inode.at/ubuntu disco/main amd64 Packages
          100 /var/lib/dpkg/status

  ProblemType: Bug
  DistroRelease: Ubuntu 19.10
  Package: grub-efi 2.02+dfsg1-12ubuntu2
  ProcVersionSignature: Ubuntu 5.3.0-18.19-generic 5.3.1
  Uname: Linux 5.3.0-18-generic x86_64
  NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
  ApportVersion: 2.20.11-0ubuntu8
  Architecture: amd64
  CurrentDesktop: ubuntu:GNOME
  Date: Sat Oct 19 23:20:07 2019
  InstallationDate: Installed on 2017-03-05 (958 days ago)
  InstallationMedia: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
  SourcePackage: grub2
  UpgradeStatus: Upgraded to eoan on 2019-10-19 (0 days ago)

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