[PATCH 2/4] tools: mkeficapsule: remove device-tree related operation

Heinrich Schuchardt xypron.glpk at gmx.de
Thu May 13 07:08:12 CEST 2021

On 5/13/21 4:33 AM, AKASHI Takahiro wrote:
> On Wed, May 12, 2021 at 12:01:32PM +0200, Heinrich Schuchardt wrote:
>> On 12.05.21 10:01, Ilias Apalodimas wrote:
>>> On Wed, May 12, 2021 at 04:49:02PM +0900, Masami Hiramatsu wrote:
>>>> Hi Ilias,
>>>> 2021年5月12日(水) 16:21 Ilias Apalodimas <ilias.apalodimas at linaro.org>:
>>>>> Akashi-san,
>>>>> On Wed, May 12, 2021 at 01:57:51PM +0900, AKASHI Takahiro wrote:
>>>>>> As we discussed, "-K" and "-D" options have nothing to do with
>>>>>> creating a capsule file. The same result can be obtained by
>>>>>> using standard commands like:
>>>>>>    === signature.dts ===
>>>>>>    /dts-v1/;
>>>>>>    /plugin/;
>>>>>>    &{/} {
>>>>>>          signature {
>>>>>>                  capsule-key = /incbin/("SIGNER.esl");
>>>>>>          };
>>>>>>    };
>>>>>>    ===
>>>>>>    $ dtc -@ -I dts -O dtb -o signature.dtbo signature.dts
>>>>>>    $ fdtoverlay -i test.dtb -o test_sig.dtb -v signature.dtbo
>>>>>> So just remove this feature.
>>>>>> (Effectively revert the commit 322c813f4bec ("mkeficapsule: Add support
>>>>>> for embedding public key in a dtb").)
>>>>>> The same feature is implemented by a shell script (tools/fdtsig.sh).
>>>>> The only reason I can see to keep this, is if mkeficapsule gets included
>>>>> intro distro packages in the future.  That would make end users life a bit
>>>>> easier, since they would need a single binary to create the whole
>>>>> CapsuleUpdate sequence.
>>>> Hmm, I think it is better to write a manpage of mkeficapsule which
>>>> also describes
>>>> how to embed the key into dtb as in the above example if it is so short.
>>>> Or, distros can package the above shell script with mkeficapsule.
>>>> Embedding a key and signing a capsule are different operations but
>>>> using the same tool may confuse users (at least me).
>>> Sure fair enough.  I am merely pointing out we need a way to explain all of
>>> those to users.
>> This is currently our only documentation:
>> https://u-boot.readthedocs.io/en/latest/board/emulation/qemu_capsule_update.html?highlight=mkeficapsule
> As I mentioned several times (and TODO in the cover letter),
> this text must be reviewed, revised and generalized
> as a platform-independent document.
> It contains a couple of errors.
>> For mkimage we have a man-page ./doc/mkimage.1 that is packaged with
>> Debians u-boot-tools package. Please, provide a similar man-page as
>> ./doc/mkeficapsule.1.
> So after all do you agree to removing "-K/-D"?

I see no need to replicate in U-Boot what is already in the device tree
compiler package.

In the current workflow the fdt command is used to load the public key.
This is insecure and not usable for production.

The public key used to verify the capsule must be built into the U-Boot
binary. This will supplant the -K and -D options.

Best regards


> Otherwise, I cannot complete the man page.
> -Takahiro Akashi
>> Best regards
>> Heinrich

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