grub2 incompatibility between at_keyboard and gfxterm modules lead to impossible to type passphrase or access ubuntu grub2 menu on a fully encrypted installation

[moo can]

Hello,

On a freshly installed Ubuntu 20.04.1 LTS (tested with Mate & Ubuntu with two different brands and configurations of laptops) fully luks encrypted systems using this guide https:/ /help.ubuntu. com/community/ Full_Disk_ Encryption_ Howto_2019 as a basis with the following configurations:

laptop 1 (Dell): x86_64 BIOS/GPT
/dev/sda1 => bios_grub
/dev/sda2 => luks encrypted LVM with VG,LV /boot, /root, /home, /swap

laptop 2 (Acer): x86_64 UEFI/GPT
/dev/sda1 => ESP
/dev/sda2 => luks encrypted LVM with VG,LV /boot, /root, /home, /swap

It's impossible with :
=> 1st stage grub: /dev/sda1 bios_grub (core.img) or ESP partition (grub.efi)
=> 2nd stage grub: /dev/sda2/ LUKS_VOL/ LVM/boot/ grub
to:
1- set and use a local grub keyboard layout (French) to type passphrase in 1st stage grub
2- access (edit mode or typing command under grub console) in 2nd stage grub

Here all my tests results from the last 3 days on the two laptops at same time with same results BIOS (Dell) or EFI (Acer):

[0] Default settings after installation :
1st stage grub: US keyboard layout (default)
2nd stage grub: gfxterm module loaded (install defaults)
=> 1st stage grub: almost impossible to type a strong passphrase with accentuated characters and special characters due to typos error and keyboard layout difference and unlock encrypted luks volume.
=> 2nd stage grub: working without trouble, can access ubuntu grub menus, edit command and type command in the grub console as normal.

[1] Modfied settings after installation : 1st stage grub only
1st stage grub: French keyboard layouts with at_keyboard module ([1A] grub core image config at the end)
2nd stage grub: gfxterm module loaded (no modification from default installation)
=> 1st stage grub: can type strong passphrase and unlock at the first attempt the luks encrypted volume
=> 2nd stage grub: Impossible to access grub menus, edit command and type command in the grub console

[2] Modfied settings after installation : 2nd stage grub only
1st stage grub: default grub core.img after installation with US layout
2nd stage grub: gfxterm module loaded (install defaults) + at_keybord, "terminal_input at_keyboard", keymap fr.gkb ([2A] grub.cfg config at the end)
=> 1st stage grub: almost impossible to type strong passphrase as in test case [0]
=> 2nd stage grub: almost Impossible to access grub menus, edit command and type command in the grub console). Each keystroke must be repeated 7 times or more to get a result (and PC speaker beep every 1x or 4x keystrokes but it's really secondary). Ressetting "terminal_output console" (by removing at_keyboard) or "terminal_input console" (by removing gfxterm) (by typing t(x7+2xbeep) e(x7+3xbeep) +r(x7+4xbeep) +m(x7+1xbeep) ...) resolved the situation.

[3] Modfied settings after installation : 1nd stage grub only
1st stage grub: French keyboard layout with at_keybord + gfxterm module
2nd stage grub: gfxterm module loaded (no modification from default installation)
=> 1st stage grub: Impossible to type strong passphrase as in test case [0] but this time it's because gfxterm and at_keyboard are loaded at the same time and each keystroke must be typed 7x or more times (sometimes more than 10 times + beep) to be taken into account, so impossible to know what you are typing because nothing is printed at screen while you type your password. By accessing grub minimal console due to a limited core.img and removing at_keybord with "terminal_input console" or removing gfxterm with "terminal_output console" resolved the situation but typing such command as set prefix=(memdisk), ... cryptomount -u xyzaabac, set root='lvmid/ Eh2HHw- Bceq-VfsK- Kz01-kaeg- dRbz-Rwcntf/ nVAE5f- GOrJ-wvu3- RTN0-mzAe- G4Oo-mzTQrN' and then the passphrase without any typos erros at first attempt with a different keyboard layout was a real challenge.
=> 2nd stage grub: Impossible to access grub menus, edit command and type command in the grub console when at_keybord (eg: "terminal_input at_keyboard") is loaded even in 1st stage grub.

Conclusion:
It seems that if grub at_keyboard module is loaded with "terminal_input at_keyboard" (to load a french keyboard layout and tested with german, italian layouts to be sure that the french one was not the source of troubles ...) even only in the 1st stage grub ... it's almost impossible to access any grub menu (edit command or console) in grub (same level) or even in another child grub as the 2nd stage if grub gfxterm module is loaded too.

So, for international users typing a strong passphrase is almost impossible without using something like "test123" or "qwerty123" and keeping access on any child grub.

For me it's something like critical because I can use a secure installation with all partition/data encrypted but I can't type a strong passphrase (eg "C0udéeM+ (@rpantÀ) ") or access any child grub menu or console if any grub at_keyboard module is loaded (at a upper level or at same level) with a gfxterm module somewhere else (at same level or at a child level).

I found an old bug report at debian.org but it seems resolved with grub 2.02+dfsg1-11.

https:/ /bugs.debian. org/cgi- bin/bugreport. cgi?bug= 741464

I opened a bug report at ubuntu:

https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1914953

in the meantime, before sending the mail to bug-grub@gnu.org, I searched on the Grub bug tracking system and read the change log for my Ubuntu focal (2.04-1ubuntu26.2) and the last one available for Ubuntu hirsuit (2.04-1ubuntu37) available at http://changelogs.ubuntu.com/changelogs/pool/main/g/grub2/grub2_2.04-1ubuntu37/changelog but find nothing revealing.

This is the first time I have reported a bug, so don't hesitate to contact me.

I apologize for my english language mistakes.
Regards,
Fabien

I can share grub core.img/grub.efi config for test case [3] if needed.

[1A] grub core.img (1st grub stage) with french keyboard layout (Dell Laptop only but I can provide too the Acer laptaop with EFI difference to generate a grub.efi)

Based on Archwiki tutorial: https:/ /wiki.archlinux .org/index. php/GRUB/ Tips_and_ tricks# Manual_ configuration_ of_core_ image_for_ early_boot

insmod echo
insmod gzio
insmod part_gpt
insmod cryptodisk
insmod luks
insmod gcry_rijndael
insmod gcry_rijndael
insmod gcry_sha256
insmod lvm
insmod ext2
insmod keylayouts
insmod at_keyboard
set root=(memdisk)
set prefix=($root)/
terminal_input at_keyboard
keymap /fr.gkb
cryptomount -u xyz123abc456def 789ghi
set root='lvmid/ Eh2HHw- Bceq-VfsK- Kz01-kaeg- dRbz-Rwcntf/ nVAE5f- GOrJ-wvu3- RTN0-mzAe- G4Oo-mzTQrN'
set prefix=($root)/grub
configfile grub.cfg

[2A] Ubuntu grub (2nd stage) modification (Dell or Acer laptop)
insmod keylayouts
insmod at_keyboard
keymap $(prefix)/fr.gkb