Problem with U-boot | Configuration Signature not being checked while booting

[Moiz Imtiaz]

Completely agreed, that a fully secure boot on pi won't be achievable
because the Root of Trust (ROT) cant be established from the BOTROM/EEPROM.
Plus Pi doesn't have any High Assurance Boot (HAB).  But given the
scenerio, whatever we can achieve i.e if we can verify the kernel, the
device tree, from the bootloader, (u-boot)  that would be great.

Currently the issue with Pi4 is that , signature verification is not being
done with u-boot, so wondering if that can be made possible.

>But that applies to the scenario where the public key is stored in the
> device tree embedded in u-boot itself as well

Just for the sake of knowledge, Isn't this the case with all u-boot, that
the public key is stored in the device tree (control FDT) and is embedded
in the u-boot.

On Sun, 12 Sep 2021, 02:34 Tom Rini, <trini at konsulko.com> wrote:

> On Sat, Sep 11, 2021 at 11:30:00PM +0200, Mark Kettenis wrote:
> > > Date: Sat, 11 Sep 2021 17:05:45 -0400
> > > From: Tom Rini <trini at konsulko.com>
> > >
> > > On Sat, Sep 11, 2021 at 09:18:46PM +0200, Mark Kettenis wrote:
> > > > > From: Moiz Imtiaz <moizimtiaz1 at gmail.com>
> > > > > Date: Sat, 11 Sep 2021 23:19:05 +0500
> > > > >
> > > > > Hi Simon,
> > > > >
> > > > > Thanks for the reply.  I already followed the steps mentioned in
> > > > > "doc/uImage.FIT/beaglebone_vboot.txt".
> > > > >
> > > > > >I wonder if rpi is not using the devicetree compiled with U-Boot,
> but
> > > > > instead one provided by the earlier-stage firmware?
> > > > >
> > > > > Not sure, but seems like this is the case. I checked and there
> isn't any
> > > > > dtb or dts for rpi4 (bcm2711-rpi-4-b) in arc/arm/dts in u-boot. I
> tried to
> > > > > add the dtb and other dts dtsi
> > > > > <
> https://github.com/raspberrypi/linux/tree/rpi-5.10.y/arch/arm64/boot/dts/broadcom
> >files
> > > > > from the raspberry pi Linux and compile them with
> CONFIG_OF_SEPARATE and
> > > > > CONFIG_OF_EMBED (one at a time) *but it couldn't even boot the
> U-Boot and
> > > > > it would just give a blank screen*. I wonder why there isn't any
> device
> > > > > tree in the U-boot repo for RPI4. Is U-boot control FDT not
> supported by
> > > > > RPI4?
> > > >
> > > > The issue with the rpi4 is that the addresses of devices move around
> > > > based on the version of the Raspberry Pi firmware you're using.  And
> > > > possibly on the amount of memory on the board as well.  So U-Boot
> > > > pretty much has to use the device tree passed by the firmware since
> > > > the device tree in the U-Boot tree would be wrong for many
> > > > combinations of firmware and hardware.
> > > >
> > > > Simon, this sort of thing is exactly the reason why I think the idea
> > > > of having all U-Boot configuration information in a single device
> tree
> > > > with the hardware description doesn't work everywhere.
> > >
> > > In this case, doesn't the Pi firmware pass along apply overlays and
> > > construct the device tree it's going to pass along, so in this case you
> > > would want to make an "overlay" for the Pi firmware to apply and pass
> > > along to U-Boot, that includes the required information?
> >
> > yes, that might work.  The overlay can be specified in the config.txt
> file.
> >
> > I think truly verified boot is impossible on the Pi though, as u-boot
> > and the overlay file will need to be stored on the uSD card of the Pi.
> > But that applies to the scenario where the public key is stored in the
> > device tree embedded in u-boot itself as well.
>
> Yes, a more general problem is that some platforms are really only
> proof-of-concept useful.  If you can't start with the ROM, you're going
> to be limited.
>
>
> --
> Tom
>