[dm-crypt] veritysetup usage question

[dm-crypt] veritysetup usage question

[Jan Pohanka]

Hello,

I'd like to use dm-verity as a part of a verified boot process on my
embedded device but I'm afraid that I still do not understand it well.

I'm able to create a hash verification data for squashfs partition,
verify it and mount it

veritysetup format rootfs.squashfs rootfs.hash
cat rootfs.squashfs rootfs.hash > srootfs.squashfs
ubiblock -c /dev/ubi0_2
ubiupdatevol /dev/ubi0_2 srootfs.squashfs
veritysetup --hash-offset=17719296 verify /dev/ubiblock0_2
/dev/ubiblock0_2 ROOT_HASH
veritysetup --hash-offset=17719296 create srootfs /dev/ubiblock0_2
/dev/ubiblock0_2 ROOT_HASH
mount -t squashfs -r /dev/mapper/srootfs /mnt

Now I can use the above verification and mount in my initramfs and it
needs the ROOT_HASH to be stored inside my bootimage. That's not a
problem but I'm thinking about future updates.
I would need to change the bootimage with a correct ROOT_HASH each
time when I update the rootfs image and it obviously is not a thing
that one wants to do.

Is there any other way to solve it using dm-verity and cryptsetup?
Otherways it is probably easier to use any hash of my squashfs image,
sign it using openssl and verify with a stable public key from the
bootimage on the device, isn't it?

best regards
Jan