OpenWrt on UEFI based x86 systems

UEFI based systems are becoming more common and it's expected at some time that newer UEFI based system doesn't contain CSM to support legacy bios mode at all.

To accommodate this, it's necessary for OpenWrt build system to generate UEFI bootable images.

There are pending commits related to add UEFI bootable OpenWrt under Jow staging repository.

Beware that the generated uefi gpt image causes kernel panic when booted on bios based system. A fix for this issue is in progress ^{1) 2)}

The commits necessary to build uefi bootable OpenWrt image are as follows.

ba837608fb3676ceaf2f463e2efc013e5d232895 tools: add libopt host build
3775232366ab903a631379ab7916514286c96e2d tools: add sgdisk host build
8752bdcbda84361e91548b2314fbf3c6e3b4d233 Generate EFI grub images for x86 platforms
b3bd0031cd8bc59c38b1c4cbb4454a415d464d15 grub: use different build directories per variant

To build the image, cherry pick those commits, i.e.

$ git remote add jow-staging https://git.openwrt.org/openwrt/staging/jow.git
$ git fetch jow-staging
$ git checkout -b uefi-capable --track origin/master # so that you can rebase easily
$ for commit in \
  ba837608fb3676ceaf2f463e2efc013e5d232895 \
  3775232366ab903a631379ab7916514286c96e2d \
  8752bdcbda84361e91548b2314fbf3c6e3b4d233 \
  b3bd0031cd8bc59c38b1c4cbb4454a415d464d15 \
  ; do \
      git cherry-pick $commmit ; done

Optionally, integrate pending changes (see footnote) to make resulting gpt images bootable on bios based systems.

$ curl -L -o patch-0001.patch "https://patchwork.ozlabs.org/patch/881131/mbox/"
$ curl -L -o patch-0002.patch "https://patchwork.ozlabs.org/patch/881132/mbox/"
$ git am ./patch-0001.patch ./patch-0002.patch

After cherry-picking those commits and integrating pending patches, run make menuconfig.

Go to Target Images and make sure that Build EFI grub images option is checked.

Select additional packages as necessary and finally save changes and exit menuconfig.

Run make as usual to build the image.

The resulting image will be available as bin/targets/x86/64/openwrt-x86-64-uefi-gpt-ext4.img.gz, which can be written to disk after decompression.

To generate signed image for use with secure boot, there is a development repository with corresponding packages feed under feature-uefi-secure-boot branch.

The repository contains changes based on Jow-staging branch to generate secure boot capable image

The related packages feed repository contains stuffs needed to sign efi binaries, i.e. gnu-efi and sbsigntool and stuffs to manipulate efi variables, i.e. efivar, efibootmgr, and efitools.

# Add the development git repository
$ git remote add devrepo https://github.com/alive4ever/openwrt
$ git fetch devrepo
$ git checkout feature-uefi-secure-boot
 
# Configure the corresponding package repository
$ echo 'git-src packages https://github.com/alive4ever/packages;feature-uefi-secure-boot' > ./feeds.conf
$ ./scripts/feeds clean
$ ./scripts/feeds update packages
$ ./scripts/feeds update -i
$ ./scripts/feeds install -a
 
# Now, configure the build system
# Select x86 as Target, x86_64 as Subtarget
# make sure to select 'Sign EFI executable binaries' under 'Target Images'
# UEFI related tools are available under Utilities section,
# which consist of efitools, efibootmgr, efivar, and sbsigntool
$ make menuconfig
 
# The certificate and key need to be generated
# to perform uefi binary signing
$ OLD_UMASK=$(umask)
$ umask 077
$ openssl req -new -x509 -sha256 \
  -days 90 -out ./db.crt \
  -subj '/CN=secure boot signing certificate' \
  -newkey rsa:2048 -nodes \
  -keyout ./db.key
$ umask $OLD_UMASK
 
# run make to generate UEFI secure bootable OpenWrt image
$ make

Remember to import db.crt (which may needs to be converted into DER or other format) into db UEFI variable to securely boot the resulting image.