96 lines
3.5 KiB
Markdown
96 lines
3.5 KiB
Markdown
# grub2-signing-extension for GRUB2
|
|
|
|
GRUB2 has got a function which automatically checks if your files in GRUB2 are signed and have a good signature. If the files aren't signed or have a bad signature GRUB2 won't run them to prevent running malicious software.
|
|
The GRUB2 signing extension are some scripts which helps you to verify, sign and unsign your GRUB2 bootloader files using gpg.
|
|
|
|
|
|
|
|
## Requirements
|
|
|
|
You need
|
|
|
|
* GRUB2 ( sys-boot/grub:2 )
|
|
* GNUpg ( app-crypt/gnupg )
|
|
|
|
|
|
|
|
## Preparation
|
|
|
|
Before you can use the signing and verification feature you need to generate a keypair as root. Please use a secure passphrase.
|
|
|
|
`# gpg --gen-key`
|
|
|
|
|
|
To make gpg able to sign and verify files in a `su` environment we need to activate the gpg-agent for root.
|
|
|
|
Edit the file _/root/.gnupg/gpg.conf_ and add the line `use-agent`.
|
|
|
|
Save the file and create _/root/.gnupg/gpg-agent.conf_ with the following content
|
|
|
|
pinentry-program /usr/bin/pinentry-curses
|
|
no-grab
|
|
default-cache-ttl 1800
|
|
|
|
|
|
|
|
## How to install the GRUB2 check\_signatures feature and using the grub2-signing-extension
|
|
|
|
First, export your public key.
|
|
|
|
`# gpg --export -o ~/pubkey`
|
|
|
|
|
|
Next step, mount /boot and (re)install GRUB2 with the following arguments:
|
|
|
|
`grub2-install /dev/sda -k /root/pubkey --modules="gcry\_sha256 gcry\_dsa gcry\_rsa"`
|
|
|
|
|
|
Now download the grub2-signing-extension and run `make install` as root. You will now have `grub2-sign`, `grub2-unsign` and `grub2-verify` as runable scripts.
|
|
|
|
|
|
To _enable_ GRUB2's check\_signatures feature insert the following content at the end of the file of */etc/grub.d/00_header*
|
|
|
|
cat << EOF
|
|
set check_signatures=enforce
|
|
EOF
|
|
|
|
|
|
Run `grub2-mkconfig -o /boot/grub/grub.cfg` to make the new configuration valid.
|
|
|
|
Now the time is come to sign your GRUB2 bootloader. Just run `grub2-sign`, enter your passphrase and that's it.
|
|
|
|
|
|
**ATTENTION:** On every change you need to run `grub2-unsign` first before you make your changes. It's also recommended to install a password in GRUB2!
|
|
|
|
|
|
|
|
## How to install a GRUB2 password
|
|
|
|
Run `grub2-mkpasswd-pbkdf2` and type a password. Please take care because in the GRUB2 standard installation the keyboard layout is set to en\_US.
|
|
Copy the content of *grub.pbkdf2.[...]* to your clipboard. Open the file */etc/grub.d/00_header* and insert this at the end of the file
|
|
|
|
cat << EOF
|
|
set superusers="yourUsername"
|
|
export superusers
|
|
password_pbkdf2 yourUsername grub.pbkdf2.[...this string from the clipboard...]
|
|
EOF
|
|
|
|
To boot GNU/Linux without automatically and without authentication open */etc/grub.d/10_linux* and change the following lines like this
|
|
|
|
echo "menuentry '$(echo "$title" | grub_quote)' ${CLASS} \$menuentry_id_option 'gnulinux-$version-$type-$boot_device_id' {" | sed "s/^/$submenu_indentation/"
|
|
else
|
|
echo "menuentry '$(echo "$os" | grub_quote)' ${CLASS} \$menuentry_id_option 'gnulinux-simple-$boot_device_id' {" | sed "s/^/$submenu_indentation/"
|
|
fi
|
|
|
|
to
|
|
|
|
echo "menuentry '$(echo "$title" | grub_quote)' --unrestricted ${CLASS} \$menuentry_id_option 'gnulinux-$version-$type-$boot_device_id' {" | sed "s/^/$submenu_indentation/"
|
|
else
|
|
echo "menuentry '$(echo "$os" | grub_quote)' --unrestricted ${CLASS} \$menuentry_id_option 'gnulinux-simple-$boot_device_id' {" | sed "s/^/$submenu_indentation/"
|
|
fi
|
|
|
|
The important changing is the flag *--unrestricted*.
|
|
|
|
|
|
Run `grub2-unsign` to unsign the bootloader. Then run `grub2-mkconfig -o /boot/grub/grub.cfg` to write the new config. After this run `grub2-sign` again to sign the new changings.
|