OpenWrt on UEFI based x86 systems

UEFI boot has been required for years now, boards that only support UEFI are common, and Intel has stated back in 2017 that “legacy” BIOS will no longer be supported after 2020.

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

As of OpenWrt a6b7c3e672764858fd294998406ae791f5964b4a, EFI-compatible images are available on the x86-64 snapshots downloads page.

To build an EFI-compatible OpenWrt image:

  • Run make menuconfig.
  • Go to Target Images and make sure that the option Build GRUB EFI images (Linux x86 or x86_64 host only) 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(s) will be available in ./bin/targets/x86/64/ (depending on the image format(s) you chose), which can be written to disk after decompression.

Note that these are disk images, not partition images, which must be written to a block device directly e.g. /dev/sdb.

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
$ git fetch devrepo
$ git checkout feature-uefi-secure-boot
# Configure the corresponding package repository
$ echo 'src-git 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.

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  • Last modified: 2021/06/28 13:50
  • by fiouz