Petitboot based bootloader

[Arthur Heymans]

Hi

I have been working on building a Petitboot, a kexec bootloader, [0]
based Linux payload using the Buildroot build system to produce a nice
bzImage that contains both linux and the initrd. It is inspired by the
Raptor Enginering HOWTO [0] and is based on op-build [1], the tool for
building OpenPOWER firmware, which also uses Buildroot and Petitboot.

One of the advantages of Petitboot is that it is fairly simple and
intuitive to use and does not require complex configuration like grub
does, while still providing a large range of hardware support since it
uses linux at its core.

A disadvantage is that a Linux + initrd payload takes up quite a bit of
space. A fairly stripped down kernel + initrd takes up ~6.9M in the
current Buildroot + Linux configuration I have. So a large flash chip or
replacing the flash with a larger one is recommended.

Coreboot can directly use this Linux payload or first load SeaBIOS which
can then chainload the Linux payload.

It is still very much a WIP and is currently aimed at Intel hardware,
but with a kernel configuration tuned to your target it should work
fine.

The repo + initial documentation:
https://github.com/ArthurHeymans/petitboot_for_coreboot

[0] Petitboot: A kexec based bootloader,
https://www.kernel.org/pub/linux/kernel/people/geoff/petitboot/petitboot.htm...

[1] Creating firmware images with petitboot and coreboot
https://secure.raptorengineering.com/content/kb/1.html

[2] OpenPower Firmware Build Environment
https://github.com/open-power/op-build

Kind Regards
--
Arthur Heymans

[Zoran Stojsavljevic]

> A disadvantage is that a Linux + initrd payload takes up quite a bit of
> space. A fairly stripped down kernel + initrd takes up ~6.9M in the
> current Buildroot + Linux configuration I have. So a large flash chip or
> replacing the flash with a larger one is recommended.

I see here PROs and CONTRAs.

One huge PRO is that petit/smallboot is excellent for consumer electronics.
For the ones which will NEVER change SW as current release of the device.
With the new device release (new version), the new enhanced SW will be put
into device. Excellent for ASICs.

One CONTRA is that it is impossible to upgrade SW in the current ASIC
context. If there will be another SW (kind of EC) with HW extension which
can control flash upgrade, which will make this device substantially more
expensive.

In other words, petitboot mainly targets consumer electronics. :-)

Best Regards,
Zoran

On Wed, Oct 26, 2016 at 3:18 AM, Arthur Heymans  wrote:
> Hi
>
> I have been working on building a Petitboot, a kexec bootloader, [0]
> based Linux payload using the Buildroot build system to produce a nice
> bzImage that contains both linux and the initrd. It is inspired by the
> Raptor Enginering HOWTO [0] and is based on op-build [1], the tool for
> building OpenPOWER firmware, which also uses Buildroot and Petitboot.
>
> One of the advantages of Petitboot is that it is fairly simple and
> intuitive to use and does not require complex configuration like grub
> does, while still providing a large range of hardware support since it
> uses linux at its core.
>
> A disadvantage is that a Linux + initrd payload takes up quite a bit of
> space. A fairly stripped down kernel + initrd takes up ~6.9M in the
> current Buildroot + Linux configuration I have. So a large flash chip or
> replacing the flash with a larger one is recommended.
>
> Coreboot can directly use this Linux payload or first load SeaBIOS which
> can then chainload the Linux payload.
>
> It is still very much a WIP and is currently aimed at Intel hardware,
> but with a kernel configuration tuned to your target it should work
> fine.
>
> The repo + initial documentation:
> https://github.com/ArthurHeymans/petitboot_for_coreboot
>
> [0] Petitboot: A kexec based bootloader,
> https://www.kernel.org/pub/linux/kernel/people/geoff/
> petitboot/petitboot.html
>
> [1] Creating firmware images with petitboot and coreboot
> https://secure.raptorengineering.com/content/kb/1.html
>
> [2] OpenPower Firmware Build Environment
> https://github.com/open-power/op-build
> Kind Regards
>
> Arthur Heymans

[Trammell Hudson]

On Wed, Oct 26, 2016 at 03:18:44AM +0200, Arthur Heymans wrote:
> I have been working on building a Petitboot, a kexec bootloader, [0]
> based Linux payload using the Buildroot build system to produce a nice
> bzImage that contains both linux and the initrd. It is inspired by the
> Raptor Enginering HOWTO [0] and is based on op-build [1], the tool for
> building OpenPOWER firmware, which also uses Buildroot and Petitboot.

Very interesting -- it is similar to my Heads bootloader / configuration
project, which is focused on how to use all of the security features
of commodity x86 systems (fully encrypted disks, TPM sealing and
attestation, SPI BP bits, tamper switches, etc), to make a slightly more
secure laptop:

https://trmm.net/Heads
> [...]
> A disadvantage is that a Linux + initrd payload takes up quite a bit of
> space. A fairly stripped down kernel + initrd takes up ~6.9M in the
> current Buildroot + Linux configuration I have. So a large flash chip or
> replacing the flash with a larger one is recommended.

My current coreboot + Linux + initrd is about 3.8 MB, which will fit
into the top 4 MB SPI flash on the x230 and can kexec into Qubes.
It has no legacy BIOS, which required a few hacks to the Xen kernel
to work.

It is still very much a WIP and quite rough around the edges;
there is no menuing system right now, nor any sort of GUI.
The installation guide is definitely a draft.

[ron minnich]

Neat! This was the original linuxbios model from 1999: kernel + minimal
initramfs in flash, so it's nice to see it coming back.

I've got something similar too, save the userland is not petitboot (I no
longer want to use C for user mode code) but Go. It's also bigger than I'd
like (about the size of the petitboot) but the security folks I talk to
like the fact that I use Go, not C. It's at github.com/u-root/u-root. In
one mode u-root is a combined binary, using a tool that rewrites all the
individual Go tools into one tool; in another mode, the only user mode
binary in flash is the go toolchain, and programs are compiled on demand
into a tmpfs. Go is fast enough to make that first compile painless. In
this second mode, the scripting language is also Go.

It's really nice to see projects using coreboot going back to putting a
real kernel in the flash. Back at Los Alamos we put linux, Plan 9, and even
some hypervisors in flash and enjoyed the flexibility it got us. We had
many thousand HPC nodes running with this model. It's not just consumer,
although there are linuxbios-based consumer systems too.

With a big enough flash the recovery and reflash is easy; you have a
fallback kernel/initramfs just as you have a fallback coreboot. I learned
the value of this the day I flash 1023 nodes with a bad image.

Thanks Arthur, that's neat stuff!

ron