libreboot/docs/gnulinux/grub_cbfs.md

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title: Modifying the GRUB Configuration in Libreboot Systems x-toc enable: true ...

This guide will go through all the steps to modify a GRUB configuration file in Libreboot; this is so that the user doesn't have to manually boot their operating system each time, by typing in commands at the GRUB command line.

For the purposes of this guide, you can either modify the GRUB configuration file that resides in the computer's ROM, or else you could modify the version that exists within the operating system itself; both options will be explained here.

How to Get the GRUB Configuration File

The first step of the process is to actually get a hold of the GRUB configuration file that we need to modify. There are two ways to do this:

1. We can extract the one that already exists within the ROM
2. We can use one of the pre-compiled ROMS supplied by the Libreboot project

However, both ways will require us to download the Libreboot Utility Archive.

Download the Libreboot Utility Archive

The Libreboot Utility Archive contains the programs that we'll need to get our grubtest.cfg file. The latest release of the Libreboot Utility Archive can be downloaded from libreboot.org, here. The quickest way to download it would be to use the wget program, which (if you don't know) allows you to download files from the internet.

If you don't already have it installed, you can install it, using the apt-get command (in Debian-based distributions):

$ sudo apt-get install wget

You can install it in Arch-based systems, using pacman:

$ sudo pacman -S wget

Once you've installed wget, use it to download the file, simply by passing it the URL as an argument; you can save the file anywhere, but for the purpose of this guide, save it in ~/Downloads (your Home directory's downloads folder). First, change the current working directory to ~/Downloads:

$ cd ~/Downloads

This guide assumes you are using the 20160907 version of Libreboot; if using a different version, modify the following commands accordingly:

$ wget https://www.mirrorservice.org/sites/libreboot.org/release/stable/20160907/\
>libreboot_r20160907_util.tar.xz

After the file is downloaded, use the tar command to extract its contents:

$ tar -xf libreboot_r20160907_util.tar.xz

After extraction, the folder will have the same name as the archive: in this case, libreboot_r20160907_util. For simplicity's sake, we'll rename it libreboot_util, using the mv command:

$ mv "libreboot_r20160907_util" "libreboot_util"

Now you have the folder with all the utilities necessary to read and modify the contents of the ROM.

Get the Necessary Utilities

Once you have the libreboot_util archive, you can find the cbfstool and flashrom utilities in libreboot_util/cbfstools/x86_64/cbfstool, and libreboot_util/flashrom/x86_64/flashrom, respectively.

NOTE: This guide assumes that you are using a device with the x86_64 architecture; if you are using a device with a different architecture (e.g., i686 or armv7l), the proper version of cbfstool and flashrom will be in that folder, inside their respective directories.

You could also compile both of these utilities; see How to Build flashrom.

flashrom is also available from the repositories; if using an Arch-based distribution, use pacman:

$ sudo pacman -S flashrom

Or, if you have a Debian-based distribution, use apt-get:

$ sudo apt-get install flashrom

Get the ROM Image

You can either work directly with one of the ROM images already included in the libreboot ROM archives, or re-use the ROM that you have currently flashed. For the purpose of this tutorial, it is assumed that your ROM image file is named libreboot.rom, so please make sure to adapt.

There are two ways to get a pre-compiled ROM image:

1. Download a Pre-Compiled Image from the Libreboot Website

For the current release, 20160907, they can be found here; please adopt this guide, if using a different version of Libreboot.

You also need to make sure that you select both the correct ROM for the device you're using, as well as the correct flash chip size (if applicable): 4mb, 8mb, or 16mb; variable flash chip sizes only apply for the Thinkpads that Libreboot supports (excluding the X60 and T60).

You can find the flash chip size, by running the following command:

# flashrom -p internal -V

Look for a line like this:

Found Macronix flash chip "MX25L6406E/MX25L6408E" (8192 kB, SPI) \
mapped at physical address 0x00000000ff800000.

Running this command on my Thinkpad X200 gives me the above result, so I know that my flash chip size is 8mb.

Once you've determined the correct ROMs and flash chip size, download them from the website. Since I'm currently using an X200 to write this guide, I'll demonstrate how to download the correct ROM images for that model.

First, we're going to navigate to the libreboot_util folder:

$ cd ~/Downloads/libreboot_util/

Then, we will download the ROM images, using wget:

$ wget https://www.mirrorservice.org/sites/libreboot.org/release/stable/\
>20160907/rom/grub/libreboot_r20160907_grub_x200_8mb.tar.xz

Extract the archive, using tar:

$ tar -xf libreboot_r20160907_grub_x200_8mb.tar.xz

Navigate to the directory that you just created:

$ cd libreboot_r20160907_grub_x200_8mb

Now that we are in the archive, we must choose the correct ROM image. To figure out the correct image, we must first parse the filenames for each ROM. For example, for the file named x200_8mb_usqwerty_vesafb.rom:

Model Name: x200
Flash Chip Size: 8mb
Country: us
Keyboard Layout: qwerty
ROM Type: vesafb or txtmode

Since I am using a QWERTY keyboard, I will ignore all the non-QWERTY options. Note that there are two types of ROMs: vesafb and txtmode; The vesafb ROM images are recommended, in most cases; txtmode ROM images come with MemTest86+, which requires text-mode, instead of the usual framebuffer used by coreboot native graphics initialization.

I'll choose x200_8mb_usqwerty_vesafb.rom; I'll copy the file (to the cbfstool directory), and rename it with one command:

$ mv "x200_8mb_usqwerty_vesafb.rom" ../cbfstool/x86_64/cbfstool/x86_64/libreboot.rom

2. Create an Image from the Current ROM

The simpler way to get a ROM image is to just create it from your current ROM, using flashrom, making sure to save it in the cbfstool folder, inside libreboot_util:

$ sudo flashrom -p internal -r ~/Downloads/libreboot_util/cbfstool/\
>x86_64/cbfstool/x86_64/libreboot.rom

If you are told to specify the chip, add the option -c {your chip} to the command, like this:

$ sudo flashrom -c MX25L6405 -p internal -r ~/Downloads/libreboot_util/\
>cbfstool/x86_64/cbfstool/x86_64/libreboot.rom

Now you are ready to extract the GRUB configuration files from the ROM, and modify them the way you want.

Copy grubtest.cfg from the ROM Image

You can check the contents of the ROM image, inside CBFS, using cbfstool. First, navigate to the cbfstool folder:

$ cd ~/Downloads/libreboot_util/cbfstool/x86_64/cbfstool/x86_64/

Then, run the cbfstool commmand, with the print option; this will display a list of all the files located in the ROM:

$ ./cbfstool libreboot.rom print

You should see grub.cfg and grubtest.cfg in the list. grub.cfg is loaded by default, with a menu entry for switching to grubtest.cfg. In this tutorial, you will first modify and test grubtest.cfg. This is to reduce the possibility of bricking your device, so DO NOT SKIP THIS!

Extract (i.e., get a copy of ) grubtest.cfg from the ROM image:

$ ./cbfstool libreboot.rom extract -n grubtest.cfg -f grubtest.cfg

By default cbfstool will extract files to the current working directory; so, grubtest.cfg should appear in the same folder as libreboot.rom.

How to Modify the GRUB Configuration File

This section will instruct the user how to modify their GRUB configuration file; whether they decide to use the version located in their operating system's / folder, or the one located in the ROM, the modifications will be the same.

Once the file is open, look for the following line (it will be towards the bottom of the file):

menuentry 'Load Operating System [o]' --hotkey='o' --unrestricted

After this line, there will be an opening bracket {, followed by a several lines of code, and then a closing bracket }; delete everything that is between those two brackets, and replace it with the following code, if you're using an Arch-based disribution (e.g., Parabola GNU+Linux-Libre):

cryptomount -a
set root='lvm/matrix-root'
linux /boot/vmlinuz-linux-libre root=/dev/matrix/root cryptdevice=/dev/sda1:root \
cryptkey=rootfs:/etc/mykeyfile
initrd /boot/initramfs-linux-libre.img

Or, replace it with this, if you are using a Debian-based distribution (e.g., Trisquel GNU+Linux):

cryptomount -a
set root='lvm/matrix-rootvol'
linux /vmlinuz root=/dev/mapper/matrix-rootvolcryptdevice=/dev/mapper/matrix-rootvol:root
initrd /initrd.img

Remember, that these names come from the instructions to install GNU+Linux on Libreboot systems, located here. If you followed different instructions, (or for some other reason, used different names), simply put the names of your root and swap volumes, in place of the ones used here.

This covers the basic changes that we can make to GRUB; however, there are some more changes that you could make, to increase the security of your GRUB configuration. If you are interested in those modifications, see the Libreboot guide on Hardening GRUB.

That's it for the modifications! Now all you need to do is follow the instructions below, in order to use this new configuration to boot your system.

Change the GRUB Configuration File that the Operating System Uses

Now that we have explained how to modify the file itself, we need to explain how to actually make our system use the new GRUB configuration file to boot.

Without Re-Flashing the ROM

To change the GRUB Configuration that our system uses, without having to re-flash the ROM, we need to take our grubest.cfg file, rename it to libreboot_grub; this is because that, by default, GRUB in Libreboot is configured to scan all partitions on the main storage for /boot/grub/libreboot_grub.cfg or /grub/libreboot_grub.cfg (for systems where /boot is on a dedicated partition), and then use it automatically.

Therefore, we need to either copy libreboot_grub.cfg to /grub, or to /boot/grub:

$ sudo cp ~/Downloads/libreboot_util/cbfstool/x86_64/cbfstool/x86_64/grubtest.cfg \
>/boot/grub    # or /grub

Now, the next time we boot our computer, GRUB (in Libreboot) will automatically switch to this configuration file. This means that you do not have to re-flash, recompile, or otherwise modify Libreboot at all!

With Re-Flashing the ROM

Changing the GRUB configuration that resides in ROM is a bit more complicated that the one in /, but most of the hard work is already done.

Change grubtest.cfg in ROM

Now that you have the modified grubtest.cfg, we need to remove the old grubtest.cfg from the ROM, and put in our new one. To remove the old one, we will use cbfstool:

$ ./cbfstool libreboot.rom remove -n grubtest.cfg

Then, add the new one to the ROM:

$ ./cbfstool libreboot.rom add -n grubtest.cfg -f grubtest.cfg -t raw

Change MAC address in ROM

The last step before flashing the new ROM, is to change the MAC address inside it. Every libreboot ROM image contains a generic MAC address; you want to make sure that your ROM image contains yours, so as to not create any problems on your network (say, for example, that multiple family members had libreboot computers, and used the same ROM image to flash those computers).

To do this, we will use the ich9gen utility, also located in libreboot_util.

First, you need to find the current MAC address of your computer; there are two ways to do this:

1. Read the white label on the bottom of the case (however, this will only work, if your motherboard has never been replaced).
2. Run ifconfig; look for your ethernet device (e.g., enpXXX in Arch-based distributions, or eth0 in Debian-based distributions), and look for a set of characters like this: 00:f3:f0:45:91:fe.

Next, you need to move libreboot.rom to the following folder; this is where the executable for ich9gen is located:

$ mv libreboot.rom ~/Downloads/libreboot_r20160907_util/ich9deblob/x86_64

Once there, run the following command, making sure to use your own MAC address, instead of what's written below:

$ ./ich9gen --macaddress XX:XX:XX:XX:XX:XX

Three new files will be created:

• ich9fdgbe_4m.bin: this is for GM45 laptops with the 4MB flash chip.
• ich9fdgbe_8m.bin: this is for GM45 laptops with the 8MB flash chip.
• ich9fdgbe_16m.bin: this is for GM45 laptops with the 16MB flash chip.

Look for the one that corresponds to the size of your ROM image; for example, if your flash chip size is 8mb, you'll want to use ich9fdgbe_8m.bin.

Now, insert this file (called the descriptor+gbe) into the ROM image, using dd:

$ dd if=ich9fdgbe_8m.bin of=libreboot.rom bs=1 count=12k conv=notrunc

Move libreboot.rom back to the libreboot_util directory:

$ mv libreboot.rom ~/Downloads/libreboot_util

You are finally ready to flash the ROM!

Flash Updated ROM Image

The last step of flashing the ROM requires us to change our current working directory to libreboot_util:

$ cd ~/Downloads/libreboot_util

Now, all we have to do is use the flash script in this directory, with the update option, using libreboot.rom as the argument:

$ sudo ./flash update libreboot.rom

Ocassionally, coreboot changes the name of a given board. If flashrom complains about a board mismatch, but you are sure that you chose the correct ROM image, then run this alternative command:

$ sudo ./flash forceupdate libreboot.rom

You will see the flashrom program running for a little while, and you might see errors, but if it says Verifying flash... VERIFIED at the end, then it’s flashed, and should boot. If you see errors, try again (and again, and again). The message, Chip content is identical to the requested image is also an indication of a successful installation.

Reboot the Computer

Now that you have flashed the image, reboot the computer. Keep pressing spacebar right after you turn it on, until you see the GRUB menu, to prevent libreboot from automatically trying to load the operating system.

Scroll down with the arrow keys, and choose the Load test configuration (grubtest.cfg) inside of CBFS option; this will switch the GRUB configuration to your test version. If all goes well, it should prompt you for a GRUB username and password, and then your LUKS password.

Once the operating system starts loading, it will prompt you for your LUKS password again. If it continues, and loads into the OS without errors, then that means your flashing attempt was a success.

Final Steps

When you are satisfied booting from grubtest.cfg, you can create a copy of grubtest.cfg, called grub.cfg.

First, go to the cbfstool directory:

$ cd ~/Downloads/libreboot_util/cbfstool/x86_64/cbfstool/x86_64/

Then, create a copy of grubest.cfg, named grub.cfg:

$ cp grubtest.cfg ./grub.cfg

Now you will use the sed command to make several changes to the file: the menu entry 'Switch to grub.cfg' will be changed to Switch to grubtest.cfg, and inside it, all instances of grub.cfg to grubtest.cfg. This is so that the main configuration still links (in the menu) to grubtest.cfg, so that you don't have to manually switch to it, in case you ever want to follow this guide again in the future (modifying the already modified config).:

$ sed -e 's:(cbfsdisk)/grub.cfg:(cbfsdisk)/grubtest.cfg:g' -e \
>'s:Switch to grub.cfg:Switch to grubtest.cfg:g' < grubtest.cfg > \
>grub.cfg

Move libreboot.rom from libreboot_util to your current directory:

$ mv ~/Downloads/libreboot_util/libreboot.rom .

Delete the grub.cfg that's already inside the ROM:

$ ./cbfstool libreboot.rom remove -n grub.cfg

Add your modified grub.cfg to the ROM:

$ ./cbfstool libreboot.rom add -n grub.cfg -f grub.cfg -t raw

Move libreboot.rom back to libreboot_util:

$ mv libreboot.rom ../..

If you don't remember how to flash it, refer back to the Flash Updated ROM Image, above; it's the same method as you used before. Afterwards, reboot the machine with your new configuration.

Copyright © 2014, 2015, 2016 Leah Rowe info@minifree.org

Copyright © 2017 Elijah Smith esmith1412@posteo.net

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License Version 1.3 or any later version published by the Free Software Foundation with no Invariant Sections, no Front Cover Texts, and no Back Cover Texts. A copy of this license is found in ../fdl-1.3.md