On fre, aug 29, 2025 at 10:29, Sascha Hauer <[email protected]> wrote: > Hi Tobias, > > On Thu, Aug 28, 2025 at 05:05:25PM +0200, Tobias Waldekranz wrote: >> Start work on adding a device mapper that is compatible with the >> corresponding subsystem in Linux. >> >> This is the foundation of several higher level abstractions, for >> example: >> >> - LVM: Linux Volume manager. Dynamically allocates logical volumes >> from one or more storage devices, manages RAID arrays, etc. >> >> - LUKS: Linux Unified Key Setup. Transparent disk >> encryption/decryption. >> >> - dm-verity: Transparent integrity checking of block devices. > > That's great stuff. We are also interested especially in dm-verity as > that would allow us to get rid of separate partitions for the Kernel > image and maybe even the FIT image format we currently use whenever we > need signed Kernel images.
We are sort of in the same boat. We wrap our rootfs in an FIT header, just because that is the only format U-Boot knows how to verify. After verification, we strip off the header, mount it, and then sysboot from it, with the kernel and DTBs in /boot on the squash. Just shipping the fs with verity data (+ possibly FEC, in the future) and a signature would be _so_ much nicer. >> >> This is part of an exploratory project for investigating how we could >> boot Infix[1] in a more platform-independent way. I.e., my intention >> is to eventually add support for some of the features mentioned above, >> assuming we don't hit any major road blocks. The rest of this letter >> just gives context for how we got here and where we would like to take >> Barebox. If that is not interesting, feel free to stop reading here :) >> >> Our idea is to relegate U-Boot to serve only as a UEFI firmware on the >> platforms where we can't escape it, and then do most of our boot logic >> in Barebox instead. Primarily we want to do this for two reasons: >> >> 1. Being able to ship barebox as an EFI app means we can use the same >> boot logic on x86 machines as we to on everything else. >> >> 2. Barebox is a much higher quality code base to work in than >> U-Boot. I'm sorry, but it just is. >> >> Barebox would thus take the place occupied by systemd-boot in many >> distro setups. So why not go with systemd-boot? >> >> 1. Infix does not run systemd as PID 1, so reusing their bootloader is >> awkward. >> >> 2. Infix ships as a single immutable filesystem image, including >> kernel, DTBs, etc. So we want to extract these files from the >> filesystem before booting the kernel. This is not supported by >> systemd-boot, AFAIK - all boot files must live on the ESP. >> >> 3. We would like to manage our devices' non-volatile storage with LVM, >> and not be bound to a fixed partition table. This will give us more >> flexibility in growing our image, efficiently having images of >> varying sizes installed, etc. >> >> Therefore, our plan is (roughly): >> >> 1. Add dm-verity support >> 2. Add dm-verity root-hash-signature verification support >> >> With that, we can securely extract kernel+DTB from our filesystem >> without having to sign them individually. > > Ok, it seems we have the same goals ;) Very glad to hear it! :) >> >> 3. Add basic LVM support, no RAID or anything, just basic (linear) >> logical volumes. >> >> This will allow us to install multiple versions of Infix on individual >> logical volumes, which Barebox can then find and boot from. >> >> 4. Add high-level helpers for working with DPS disks and DDI images. >> >> I really like the Linux Userspace API Group's thinking around >> Discoverable Partitions Specification (DPS) and Discoverable Disk >> Images (DDI). I think it would be great if Barebox had knowledge about >> these patterns, and could automatically set up the dm-verity >> configuration for a partition when available, for example. > > I haven't looked into this yet, but it sounds good. It's a good thing > when barebox can just do the right thing without much configuration. > >> >> My hope is that this plan sparks some ideas and reflections. If so, I >> would love to hear them. If not, sorry for the wall of text :) > > Well I am very open for adding DM and dm-verity support to barebox. We > would likely have done it anyway at some point, but that could have > taken some time. Cool! I did a toy implementation in Python yesterday, just to convince myself I understood how it works, and it was actually very straight forward. So if this series is eventually merged, I hope to follow up with an implementation of dm-verity pretty quickly. > Sascha > > -- > Pengutronix e.K. | | > Steuerwalder Str. 21 | http://www.pengutronix.de/ | > 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
