Changes/Include security modules in efi Grub2

Include several modules in the EFI build of Grub2 for security use-cases

Summary

Include Grub's "verify," "cryptodisk" and "luks" modules in grubx64.efi of the 'grub2-efi-x64' package.

Note: The dependencies "gcry_rijndael," "gcry_sha256," "procfs," "archelp," "mpi," "gcry_rsa" and "gcry_sha1" must also be included.

Owner

• Name: Name here
• Email: Email address here
• Release notes owner:

Current status

• Targeted release: Fedora 31
• Last updated: 2019-04-28
• Tracker bug: <will be assigned by the Wrangler>

Detailed Description

Users utilising secure boot functionality on the UEFI platform cannot insert modules that aren't in grubx64.efi. Paradoxically, this means that security-conscious users cannot use grub's verify module, or employ (near) full disk encryption using cryptodisk and luks.

The security benefits of signature verification would reach more users if Fedora automated it by incorporating the process into grub2-mkconfig.

For the long-term, to grant flexibility with grub2 modules on secure boot instances, it may be advisable to sign the .mod files in the 'grub2-efi-x64-modules' package, modify grub2-mkconfig (or -install) to copy the necessary modules into the EFI partition when required by the user's configuration and then allow inserting of signed modules in secure boot instances.

Benefit to Fedora

This change will allow users to gain trust in the integrity of early-launch code either through verification of signatures (particularly useful for initramfs, which is particularly vulnerable to possible offline modification) or encryption of the boot partition.

Scope

• Proposal owners: Modify grub.macros file to include the above-mentioned modules in the GRUB_MODULES variable.

• Other developers: N/A (not a System Wide Change)

• Release engineering: #Releng issue number (a check of an impact with Release Engineering is needed)
  • List of deliverables: N/A (not a System Wide Change)

• Policies and guidelines: N/A (not a System Wide Change)

• Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

Change only adds modules, so existing users should have no problems.

How To Test

For "verify":

1. Generate an RSA signing key with gpg --gen-key, then export it with gpg --export > pubkey and copy it to the EFI partition. You can also export the private key (gpg --export-secret-keys > seckey), but the signing process doesn't require it and gpg will get the key from its own directory.

2. Add "insmod verify," "trust (hd0,gpt1)/efi/fedora/<gpg key>" (change this based on your environment, grub may inherit this from shim's MOK) and "set check_signatures=enforce" to /etc/default/40_custom

3. Run grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg

4. Create a file, /tmp/pass, with the key's passphrase, then execute: for x in $(find /boot -name "*.cfg" -or -name "*.mod" -or -name "vmlinuz*" -or -name "initramfs*" -or -name "grubenv"); do gpg --batch --detach-sign --passphrase-fd 0 $x < /tmp/pass; done. Then, shred /tmp/pass

5. Reboot. If system starts, backup and remove .sig files. If system does not start this time, change is successful

(To recover from a now non-booting system, open the grub terminal and execute set check_signatures=no. The system should then boot, and .sig files can be replaced or regenerated.)

For cryptography modules:

1. Backup boot partition

2. Run cryptsetup luksFormat /dev/sda2 --type luks1 (change this based on your environment to boot's block device) Note: If filesystem root is also encrypted, it is recommended that the same password be used for boot as for root to decrease the amount of engagement required at start-up. Consider using --iter-time with a low time (in ms), as grub seems single-threaded. Additionally, do not use twofish, serpent (for encryption) or whirlpool (for hashing) here, as this change does not account for them

3. Open luks container, run mkfs.ext4 /dev/mapper/luks-<your luks UUID> and restore backup

4. Add GRUB_ENABLE_CRYPTODISK=y to /etc/default/grub

5. Confirm that /etc/fstab has the correct UUID for /boot

6. Add an entry for the boot container to /etc/crypttab, then run dracut -vf --regenerate-all

7. Run grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg

8. Reboot. Grub should ask for the password created in step 2. If system then starts, change is successful

(If filesystem root is also encrypted, user will be asked for a password twice. This can be mitigated with a keyfile for filesystem root, or use of the clevis package and likely, a tpm.)

User Experience

Users may optionally elect to verify the integrity of boot code either through verification of digital signatures or encryption of the boot partition.

Dependencies

Grub2-efi-x64-modules and grub2-tools-* depend on this package, but require no change.

Contingency Plan

• Contingency mechanism: (What to do? Who will do it?) Revert the shipped configuration
• Contingency deadline: Beta freeze
• Blocks release? N/A (not a System Wide Change)
• Blocks product? No

Documentation

https://www.gnu.org/software/grub/manual/grub/html_node/Using-digital-signatures.html

https://wiki.archlinux.org/index.php/Dm-crypt/Encrypting_an_entire_system#Encrypted_boot_partition_(GRUB)

Release Notes

Fedora now supports Grub's detached verify and cryptodisk functionality natively, even on secure boot systems.