On 12/11/19 12:36 PM, Cristian Ciocaltea wrote:
On Wed, Dec 11, 2019 at 11:13:28AM +0100, Heinrich Schuchardt wrote:
On 12/11/19 9:54 AM, Cristian Ciocaltea wrote:
- Create a public/private key pair
$ openssl genpkey -algorithm RSA -out ${DEV_KEY} \ -pkeyopt rsa_keygen_bits:2048 -pkeyopt rsa_keygen_pubexp:65537
- Create a certificate containing the public key
$ openssl req -batch -new -x509 -key ${DEV_KEY} -out ${DEV_CRT}
- Dump QEMU virt board DTB
$ qemu-system-arm -nographic -M virt,dumpdtb=${BOARD_DTB} \ -cpu cortex-a15 -smp 1 -m 512 -bios u-boot.bin [...]
- Create (unsigned) FIT image and put the public key into DTB, with the 'required' property set, telling U-Boot that this key MUST be verified for the image to be valid
$ mkimage -f ${FIT_ITS} -K ${BOARD_DTB} -k ${KEYS_DIR} -r ${FIT_IMG}
- Sign the FIT image
$ fit_check_sign -f ${FIT_IMG} -k ${BOARD_DTB}
Thanks for the description
tools/fit_check_sign does not change any file. The signature is added in step 4.
You are right, I've taken the commands from a script I use to automate the whole procedure and I've just missed the verification step.
What seems to be missing in the U-Boot build system is the capability to specify a public key in the configuation file to automatically include the public key in the generated dtbs similar to Linux's CONFIG_SYSTEM_TRUSTED_KEYS.
That would be a nice addition. Currently it is only possible to pass the 'EXT_DTB' parameter to 'make' in order to provide the path to an external DTB file to be put in the U-Boot image.
I guess the first thing to do is to change mkimage such that we can add a public key to a dtb without passing any kernel image:
tools/mkimage -K filename.dtb -k keys
Currently this is not accepted by mkimage.
Next we can then integrate this command into the build process.
Best regards
Heinrich