[Bug 2142406] Re: [SC8280XP] Live ISO GRUB fails to load — embedded config prefers internal SSD over live media

[Jens Glathe]

Oof actually, yeah :) The X13s first install was a wild bootstrap via RPi 23.04 preinstalled desktop image, and it still has /.disk/info from April 18, 2023. Wow. Thanks for explaining. Maybe this can be hardened a bit, though. 
On the Windows Dev Kit, though, this is not the case. It has a legit 25.04 install from the plucky concept X1E image, so no /.disk/info there - just checked to be sure.

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Title:
  [SC8280XP] Live ISO GRUB fails to load — embedded config prefers
  internal SSD over live media

Status in grub2 package in Ubuntu:
  New

Bug description:
  Booting the Ubuntu 26.04 daily-live ARM64 ISO on SC8280XP (ThinkPad
  X13s, Windows Dev Kit 2023) results in GRUB falling back to the
  installed GRUB on the internal SSD instead of the live environment.

  Reproduction:
  1. Boot latest 26.04 daily ARM64 live ISO (USB).
  2. GRUB loads but immediately shows “/boot/ not found” (or similar) and boots the SSD’s Ubuntu instead of the live desktop.

  The embedded config in EFI/BOOT/grubaa64.efi (extracted from the ISO
  via binwalk + unsquashfs) is:

  ```
  if [ -z "$prefix" -o ! -e "$prefix" ]; then
  if ! search --file --set=root /.disk/info; then
  search --file --set=root /.disk/mini-info
  fi
  set prefix=($root)/boot/grub
  fi
  if [ -e $prefix/arm64-efi/grub.cfg ]; then
  source $prefix/arm64-efi/grub.cfg
  elif [ -e $prefix/grub.cfg ]; then
  source $prefix/grub.cfg
  else
  source $cmdpath/grub.cfg
  fi
  ```

  Because the `search --file` for `/.disk/info` (or `/.disk/mini-info`)
  succeeds on the internal SSD, GRUB sets prefix to the installed system
  and sources its grub.cfg. There is no reliable way for the live media
  to take precedence over this baked-in logic.

  This makes the live ISO effectively unusable on SC8280XP machines that
  already have Ubuntu installed — a very common testing/development
  scenario.

  Expected behaviour:
  The live ISO should always prefer its own configuration and boot the live environment, regardless of what is installed internally.

  Workaround:
  Replacing grubaa64.efi with an older binary allows the live config to work again, but this breaks Secure Boot and is not acceptable for normal use.

  This appears to be a regression in how the live GRUB EFI image is
  built for 26.04.

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