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bootloader: grub: Add support for loading an additional initrd.

In order to be able to provide decryption keys for the LUKS device, they need
to be available in the initial ram disk.  However they cannot be stored inside
the usual initrd, since it is stored in the store and being a
world-readable (as files in the store are) is not a desired property for a
initrd containing decryption keys.  This commit adds an option to load
additional initrd during the boot, one that is not stored inside the store and
therefore can contain secrets.

Since only grub supports encrypted /boot, only grub is modified to use the
extra-initrd.  There is no use case for the other bootloaders.

* doc/guix.texi (Bootloader Configuration): Describe the new extra-initrd
field.
* gnu/bootloader.scm (<bootloader-configuration>): Add extra-initrd field.
* gnu/bootloader/grub.scm (make-grub-configuration): Use the extra-initrd
field.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Change-Id: I995989bb623bb594ccdafbf4a1a6de941bd4189f
master
Tomas Volf 2024-01-11 18:35:40 +01:00 committed by Ludovic Courtès
parent d082312ef7
commit 086850e5b2
No known key found for this signature in database
GPG Key ID: 090B11993D9AEBB5
3 changed files with 59 additions and 3 deletions

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@ -41070,6 +41070,55 @@ This option in enabled by default. In some cases involving the
@code{u-boot} bootloader, where the device tree has already been loaded
in RAM, it can be handy to disable the option by setting it to
@code{#f}.
@item @code{extra-initrd} (default: @code{#f})
File name of an additional initrd to load during the boot. It may or
may not point to a file in the store, but the main use case is for
out-of-store files containing secrets.
In order to be able to provide decryption keys for the LUKS device, they
need to be available in the initial ram disk. However they cannot be
stored inside the usual initrd, since it is stored in the store and
being a world-readable (as files in the store are) is not a desired
property for a initrd containing decryption keys. You can therefore use
this field to instruct GRUB to also load a manually created initrd not
stored in the store.
For any use case not involving secrets, you should use regular initrd
(@pxref{operating-system Reference, @code{initrd}}) instead.
Suitable image can be created for example like this:
@example
echo /key-file.bin | cpio -oH newc >/key-file.cpio
chmod 0000 /key-file.cpio
@end example
After it is created, you can use it in this manner:
@lisp
;; Operating system with encrypted boot partition
(operating-system
...
(bootloader (bootloader-configuration
(bootloader grub-efi-bootloader)
(targets '("/boot/efi"))
;; Load the initrd with a key file
(extra-initrd "/key-file.cpio")))
(mapped-devices
(list (mapped-device
(source (uuid "12345678-1234-1234-1234-123456789abc"))
(target "my-root")
(type (luks-device-mapping-with-options
;; And use it to unlock the root device
#:key-file "/key-file.bin"))))))
@end lisp
Be careful when using this option, since pointing to a file that is not
readable by the grub while booting will cause the boot to fail and
require a manual edit of the initrd line in the grub menu.
Currently only supported by GRUB.
@end table
@end deftp

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@ -6,6 +6,7 @@
;;; Copyright © 2020 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
;;; Copyright © 2022 Josselin Poiret <dev@jpoiret.xyz>
;;; Copyright © 2022 Reza Alizadeh Majd <r.majd@pantherx.org>
;;; Copyright © 2024 Tomas Volf <~@wolfsden.cz>
;;;
;;; This file is part of GNU Guix.
;;;
@ -77,6 +78,7 @@
bootloader-configuration-serial-unit
bootloader-configuration-serial-speed
bootloader-configuration-device-tree-support?
bootloader-configuration-extra-initrd
%bootloaders
lookup-bootloader-by-name
@ -279,7 +281,9 @@ instead~%")))
(serial-speed bootloader-configuration-serial-speed
(default #f)) ;integer | #f
(device-tree-support? bootloader-configuration-device-tree-support?
(default #t))) ;boolean
(default #t)) ;boolean
(extra-initrd bootloader-configuration-extra-initrd
(default #f))) ;string | #f
(define-deprecated (bootloader-configuration-target config)
bootloader-configuration-targets

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@ -9,6 +9,7 @@
;;; Copyright © 2020 Stefan <stefan-guix@vodafonemail.de>
;;; Copyright © 2022 Karl Hallsby <karl@hallsby.com>
;;; Copyright © 2022 Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
;;; Copyright © 2024 Tomas Volf <~@wolfsden.cz>
;;;
;;; This file is part of GNU Guix.
;;;
@ -386,7 +387,8 @@ when booting a root file system on a Btrfs subvolume."
store-directory-prefix))
(initrd (normalize-file (menu-entry-initrd entry)
device-mount-point
store-directory-prefix)))
store-directory-prefix))
(extra-initrd (bootloader-configuration-extra-initrd config)))
;; Here DEVICE is the store and DEVICE-MOUNT-POINT is its mount point.
;; Use the right file names for LINUX and INITRD in case
;; DEVICE-MOUNT-POINT is not "/", meaning that the store is on a
@ -397,11 +399,12 @@ when booting a root file system on a Btrfs subvolume."
#~(format port "menuentry ~s {
~a
linux ~a ~a
initrd ~a
initrd ~a ~a
}~%"
#$label
#$(grub-root-search device linux)
#$linux (string-join (list #$@arguments))
(or #$extra-initrd "")
#$initrd)))
(multiboot-kernel
(let* ((kernel (menu-entry-multiboot-kernel entry))