[Bug 1851311] Re: loopback command hangs in 2.04 under UEFI

[Zakhar]

Clean 20.04, I confirm the bug.

There is a very simple way to reproduce the bug, **without even booting
an O.S.**

- Set your machine to boot in EFI mode
- From the Grub (2.04) Menu, enter command mode (by pressing the key 'c')
- Set the root to where you have your iso files:

For instance:
root=hd1,msdos5

- Then just list one of your Iso file:

ls /path/to/iso/ubuntu-20.04-desktop-amd64.iso
error out of memory

That's it, just 2 commands on Grub to reproduce the bug.

Obviously, since you cannot even list the iso file, there is no way you
can loopback on it or boot it.

I also confirm that "rmmod tpm" did the trick and is a valid workaround
until a fix arrives.

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https://bugs.launchpad.net/bugs/1851311

Title:
  loopback command hangs in 2.04 under UEFI

Status in grub2 package in Ubuntu:
  Confirmed
Status in grub2 package in Debian:
  New

Bug description:
  Trying to loop mount ISO.

  Installed grub 2.04 to flash drive in UEFI mode from 19.10
  Flash drive does not boot and gives Out of memory error & no server error. Must load kernel first.

  Re-installed grub from 18.04 to same flash drive using same boot stanza.
  Booted without issue.

  From 18.04
  fred at Bionic-Z170N:~$ grub-install -V
  grub-install (GRUB) 2.02-2ubuntu8.13

  from 19.10
  fred at fred-Z170N-eoan:~$ grub-install -V
  grub-install (GRUB) 2.04-1ubuntu12

  Boot stanza that works in 2.02 but not in 2.04

  menuentry "Focal Live ISO" {
  set isofile="/ISO/focal-desktop-amd64.iso"
  loopback loop (hd0,1)$isofile
      linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile toram noeject
      initrd (loop)/casper/initrd
  }

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