From: Quirin Gylstorff <quirin.gylstorff@...>

Signed-off-by: Quirin Gylstorff <quirin.gylstorff@...>
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+# Efibootguard Secure boot
+
+This document describes how to generate a secure boot capable image with
+[efibootguard](https://github.com/siemens/efibootguard).
+
+## Description
+
+The image build signs the efibootguard bootloader (bootx64.efi) and generates
+a signed [unified kernel image](https://systemd.io/BOOT_LOADER_SPECIFICATION/).
+A unified kernel image packs the kernel, initramfs and the kernel command-line
+in one binary object. As the kernel command-line is immutable after the build
+process, the previous selection of the root file system with a command-line parameter is no longer
+possible. Therefore the selection of the root file-system occurs now in the initramfs.
+
+The image uses an A/B partition layout to update the root file system. The sample implementation to
+select the root file system generates a uuid and stores the id in /etc/os-release and in the initramfs.
+During boot the initramfs compares its own uuid with the uuid stored in /etc/os-release of each rootfs.
+If a match is found the rootfs is used for the boot.
+
+## Adaptation for Images
+
+### WIC
+The following elements must be present in a wks file to create a secure boot capable image.
+
+```
+part --source efibootguard-efi --sourceparams "signwith=<script or executable to sign the image>"
+part --source efibootguard-boot --sourceparams "uefikernel=<name of the unified kernel>,signwith=<script or executable to sign the image>"
+```
+
+#### Script or executable to sign the image
+
+The wic plugins for the [bootloader](./scripts/lib/wic/plugins/source/efibootguard-efi.py)
+and [boot partition](./scripts/lib/wic/plugins/source/efibootguard-boot.py) require an
+executable or script with the following interface:
+```
+<script_name> <inputfile> <outputfile>
+```
+- script name: name and path of the script added with
+`--sourceparams "signwith=/usr/bin/sign_secure_image.sh"` to the wic image
+- inputfile: path and name of the file to be signed
+- outputfile: path and name of the signed input
+
+Supply the script name and path to wic by adding
+`signwith=<path and name of the script to sign>"` to sourceparams of the partition.
+
+
+### Existing packages to sign an image
+
+#### ebg-secure-boot-snakeoil
+
+This package uses the snakeoil key and certificate from the ovmf package(0.0~20200229-2)
+backported from Debian bullseye and signs the image.
+
+#### ebg-secure-boot-secrets
+This package takes a user-generated certificate and adds it to the build system.
+The following variable and steps are necessary to build a secure boot capable image:
+- Set certification information to sign and verify the image with:
+ - SB_CERTDB: The directory containing the certificate database create with certutil
+ - SB_VERIFY_CERT: The certificate to verify the signing process
+ - SB_KEY_NAME: Name of the key in the certificate database
+- if necessary change the script to select the boot partition after an update
+ - recipes-support/initramfs-config/files/initramfs.selectrootfs.script
+
+The files referred by SB_CERTDB and SB_VERIFY_CERT must be store in `recipes-devtools/ebg-secure-boot-secrets/files/`
+
+## QEMU
+
+Set up a secure boot test environment with [QEMU](https://www.qemu.org/)
+
+### Prerequisites
+
+- OVMF from edk2 release edk2-stable201911 or newer
+ - This documentation was tested under Debian 10 with OVMF (0.0~20200229-2) backported from Debian
+ bullseye
+- efitools for KeyTool.efi
+ - This documentation was tested under Debian 10 with efitools (1.9.2-1) backported from Debian bullseye
+- libnss3-tools
+
+### Debian Snakeoil keys
+
+The build copies the Debian Snakeoil keys to the directory `./build/tmp/deploy/images/<machine>/OVMF. Y
+u can use them as described in section [Start Image](### Start the image).
+
+### Generate Keys
+
+#### Reuse exiting keys
+
+It is possible to use exiting keys like /usr/share/ovmf/PkKek-1-snakeoil.pem' from Debian
+by executing the script `scripts/generate-sb-db-from-existing-certificate.sh`, e.g.:
+```
+export SB_NAME=<name for the secureboot config>
+export SB_KEYDIR=<location to store the database>
+export INKEY=<secret key of the certificate>
+export INCERT=<certificate>
+export INNICK=<name of the certificate in the database>
+scripts/generate-sb-db-from-existing-certificate.sh
+```
+This will create the directory `SB_KEYDIR` and will store the `${SB_NAME}certdb` with the given name.
+
+Copy the used certificate and database to `recipes-devtools/ebg-secure-boot-secrets/files/`
+
+#### Generate keys
+
+To generate the necessary keys and information to test secure-boot with QEMU
+execute the script `scripts/generate_secure_boot_keys.sh`
+
+##### Add Keys to OVMF
+1. Create a folder and copy the generated keys and KeyTool.efi
+(in Debian the file can be found at: /lib/efitools/x86_64-linux-gnu/KeyTool.efi) to the folder
+```
+mkdir secureboot-tools
+cp -r keys secureboot-tools
+cp /lib/efitools/x86_64-linux-gnu/KeyTool.efi secureboot-tools
+```
+2. Copy the file OVMF_VARS.fd (in Debian the file can be found at /usr/share/OVMF/OVMF_VARS.fd)
+to the current directory. OVMF_VARS.fd contains no keys can be instrumented for secureboot.
+3. Start QEMU with the script scripts/start-efishell.sh
+```
+scripts/start-efishell.sh secureboot-tools
+```
+4. Start the KeyTool.efi FS0:\KeyTool.efi and execute the the following steps:
+ -> "Edit Keys"
+ -> "The Allowed Signatures Database (db)"
+ -> "Add New Key"
+ -> Change/Confirm device
+ -> Select "DB.esl" file
+ -> "The Key Exchange Key Database (KEK)"
+ -> "Add New Key"
+ -> Change/Confirm device
+ -> Select "KEK.esl" file
+ -> "The Platform Key (PK)
+ -> "Replace Key(s)"
+ -> Change/Confirm device
+ -> Select "PK.auth" file
+5. quit QEMU
+
+### Build image
+
+Build the image with a signed efibootguard and unified kernel image
+with the snakeoil keys by executing:
+```
+kas-docker --isar build kas-cip.yml:kas/board/qemu-amd64.yml:kas/opt/ebg-swu.yml:kas/opt/ebg-secure-boot-snakeoil.yml
+```
+
+For user-generated keys, create a new option file. This option file could look like this:
+```
+header:
+ version: 8
+ includes:
+ - opt/ebg-swu.yml
+ - opt/ebg-secure-boot-initramfs.yml
+
+local_conf_header:
+ secure-boot: |
+ IMAGER_BUILD_DEPS += "ebg-secure-boot-secrets"
+ IMAGER_INSTALL += "ebg-secure-boot-secrets"
+ user-keys:
+ SB_CERTDB = "democertdb"
+ SB_VERIFY_CERT = "demo.crt"
+ SB_KEY_NAME = "demo"
+```
+
+Replace `demo` with the name of the user-generated certificates.
+
+### Start the image
+
+#### Debian snakeoil
+
+Start the image with the following command:
+```
+SECURE_BOOT=y \
+./start-qemu.sh amd64
+```
+
+The default `OVMF_VARS.snakeoil.fd` boot to the EFI shell. To boot Linux enter the following command:
+```
+FS0:\EFI\BOOT\bootx64.efi
+```
+To change the boot behavior, enter `exit` in the shell to enter the bios and change the boot order.
+
+#### User-generated keys
+Start the image with the following command:
+```
+SECURE_BOOT=y \
+OVMF_CODE=./build/tmp/deploy/images/qemu-amd64/OVMF/OVMF_CODE.secboot.fd \
+OVMF_VARS=<path to the modified OVMF_VARS.fd> \
+./start-qemu.sh amd64
+```
+# Example: Update the image
+
+For updating the image, the following steps are necessary:
+- [Build the image with snakeoil keys](### Build image)
+- save the generated swu `build/tmp/deploy/images/qemu-amd64/cip-core-image-cip-core-buster-qemu-amd64.swu` to /tmp
+- modify the image for example add a new version to the image by adding `PV=2.0.0` to
+ [cip-core-image.bb](recipes-core/images/cip-core-image.bb)
+- start the new target and copy the swu `cip-core-image-cip-core-buster-qemu-amd64.swu`
+ to the running system, e.g.:
+```
+SECURE=y ./start-qemu.sh amd64 -virtfs local,path=/tmp,mount_tag=host0,security_model=passthrough,id=host0
+```
+- mount `host0` on target with:
+```
+mount -t 9p -o trans=virtio,version=9p2000.L host0 /mnt
+```
+- check which partition is booted, e.g. with `lsblk`:
+```
+root@demo:/mnt# lsblk
+NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
+sda 8:0 0 2G 0 disk
+├─sda1 8:1 0 16.4M 0 part
+├─sda2 8:2 0 32M 0 part
+├─sda3 8:3 0 32M 0 part
+├─sda4 8:4 0 1000M 0 part /
+└─sda5 8:5 0 1000M 0 part
+```
+
+- install with `swupdate -i /mnt/cip-core-image-cip-core-buster-qemu-amd64.swu`
+- reboot
+- check which partition is booted, e.g. with `lsblk`. The rootfs should have changed:
+```
+root@demo:~# lsblk
+NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
+sda 8:0 0 2G 0 disk
+├─sda1 8:1 0 16.4M 0 part
+├─sda2 8:2 0 32M 0 part
+├─sda3 8:3 0 32M 0 part
+├─sda4 8:4 0 1000M 0 part
+└─sda5 8:5 0 1000M 0 part /
+```
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2.20.1