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= Include several modules in the EFI build of Grub2 for security use-cases <!-- The name of your change proposal --> =
 
= Include several modules in the EFI build of Grub2 for security use-cases <!-- The name of your change proposal --> =

Revision as of 02:40, 25 March 2019

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

Summary

Include Grub's "verify," "cryptodisk" and "luks" modules (and if necessary, relevant gcry modules) in the EFI build of Grub2.

Owner

Current status

  • Targeted release: Fedora 31
  • Last updated: 2019-03-25
  • Tracker bug: <will be assigned by the Wrangler>

Detailed Description

Long-term, it may be advisable to sign the .mod files in the 'grub-efi-*-modules' package, modify grub2-mkconfig (or -install) to copy the necessary modules into the EFI partition and then allowing inserting of signed modules in secure boot instances.

Benefit to Fedora

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

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 possibly offline modification) or encryption of the boot partition.

Perhaps long-term, Fedora can use the verify module to automatically provide detached signature-based verification of the boot files.

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)

This feature will not require a rebuild of any other packages nor of the installer image. If desired, change can be delivered after install as an update.

  • 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 a signing key with "gpg --gen-key" and copy it to the EFI partition

2. Add "trust <gpg key>" (but 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 "initrd*" -or -name "grubenv"); do gpg --batch --detach-sign --passphrase-fd 0 $x < /tmp/pass; done. Then, shred /tmp/pass.

5. Reboot. If system starts, change is successful.


For cryptography modules:

1. Backup boot partition

2. Run cryptsetup luksFormat <boot partition's block device, for example, /dev/sda2> --type luks1

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

7. 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 may 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 early-launch code either through verification of signatures or encryption of the boot partition.

Dependencies

Grub-efi-*-modules and grub-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.