[PATCH] Documentation: boards: imx: add some HAB documentation

[Sascha Hauer]

On Tue, Sep 19, 2023 at 04:15:52PM +0200, Ahmad Fatoum wrote:
> We could use some extra documentation on how to use the hab command to
> fuse a SoC and what output should be expected. Add this to the
> documentation. Procedure was done with HABv4 on i.MX8MM, which is not
> yet upstream[1], but should be equivalent for i.MX6.

Nice read! thanks, applied

Sascha

> 
> [1]: https://lore.barebox.org/barebox/20230705144219.504194-1-r.czerwinski@pengutronix.de/
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
>  Documentation/boards/imx.rst | 47 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/Documentation/boards/imx.rst b/Documentation/boards/imx.rst
> index 17465efdd9be..5a4f52b392d5 100644
> --- a/Documentation/boards/imx.rst
> +++ b/Documentation/boards/imx.rst
> @@ -178,6 +178,53 @@ It must be included in the board's flash header:
>  
>  Analogous to HABv4 options and a template exist for HABv3.
>  
> +To verify HAB working as intended, install the ``barebox-*-s.img`` onto the
> +boot medium and trigger a power-on reset. barebox will read the HAB log on
> +startup and report any errors it finds. A good unfused boot looks like this::
> +
> +  HABv4: Status: Operation completed successfully (0xf0)
> +  HABv4: Config: Non-secure IC (0xf0)
> +  HABv4: State: Non-secure state (0x66)
> +  HABv4: No HAB Failure Events Found!
> +
> +To have the bootrom verify the barebox binary, the SRK hash needs to be burnt
> +into the fuses. As fuses can't be unburnt, the ``hab`` command should be used
> +instead of direct device access to not risk writing unrelated fuses::
> +
> +  barebox$ hab -p -s SRK_1_2_3_4_fuse.bin
> +
> +Afterwards, images signed with a different key will trigger errors at barebox
> +startup, but system will still be able to boot to shell.
> +
> +To have the BootROM refuse booting differently signed images, the ``SRK_LOCK``
> +fuse needs to be burnt::
> +
> +  barebox$ hab -p -l
> +
> +On next startup, barebox will report that the system is now locked::
> +
> +  HABv4: Status: Operation completed successfully (0xf0)
> +  HABv4: Config: Secure IC (0xcc)
> +  HABv4: State: Trusted state (0x99)
> +  HABv4: No HAB Failure Events Found!
> +
> +This can also be seen with the ``hab -i`` command::
> +
> +  Current SRK hash: <some non-zero value>
> +  secure mode
> +
> +Similarly, on supported SoCs, the ``bootrom -l`` command will indicate that
> +device is closed. Example output after booting via ``imx-usb-loader``::
> +
> +
> +  [e0] Internal use
> +  [11] Boot mode is Boot from Serial Download
> +  [23] Secure config is Closed
> +  [41] FUSE_SEL_VALUE Fuse is blown
> +  [d0] Enters serial download processing
> +  [a0] Image authentication result: PASS (0x000000f0) @3506438144 ticks
> +  [00] End of list
> +
>  Secure Boot on i.MX6
>  ~~~~~~~~~~~~~~~~~~~~
>  
> -- 
> 2.39.2
> 
> 
> 

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