[PATCH 0/2] RFC: add fdt_add_pubkey tool

Jan Kiszka jan.kiszka at siemens.com
Tue Nov 9 11:07:04 CET 2021

On 09.11.21 10:37, Roman Kopytin wrote:
> Can we have discussion with code lines? For me it is not very clear, because it isn't my code.

Please do not top-post.

> -----Original Message-----
> From: Jan Kiszka <jan.kiszka at siemens.com> 
> Sent: Tuesday, November 9, 2021 12:17 PM
> To: Roman Kopytin <Roman.Kopytin at kaspersky.com>; u-boot at lists.denx.de; Rasmus Villemoes <rasmus.villemoes at prevas.dk>
> Subject: Re: [PATCH 0/2] RFC: add fdt_add_pubkey tool
> On 08.11.21 16:28, Roman Kopytin wrote:
>> In order to reduce the coupling between building the kernel and 
>> U-Boot, I'd like a tool that can add a public key to U-Boot's dtb 
>> without simultaneously signing a FIT image. That tool doesn't seem to 
>> exist, so I stole the necessary pieces from mkimage et al and put it 
>> in a single .c file.
>> I'm still working on the details of my proposed "require just k out 
>> these n required keys" and how it should be implemented, but it will 
>> probably involve teaching this tool a bunch of new options. These 
>> patches are not necessarily ready for inclusion (unless someone else 
>> finds fdt_add_pubkey useful as is), but I thought I might as well send 
>> it out for early comments.
> I'd also like to see the usage of this hooked into the build process.
> And to my understanding of [1], that approach will provide a feature that permits hooking with the build but would expect the key as dtsi fragment. Can we consolidate the approaches?
> My current vision of a user interface would be a Kconfig option that takes a list of key files to be injected. Maybe make that three lists, one for "required=image", one for "required=conf", and one for optional keys (if that has a use case in practice, no idea).
> Jan
> [1]
> https://lore.kernel.org/u-boot/20210928085651.619892-1-rasmus.villemoes@prevas.dk/
> --
> Siemens AG, T RDA IOT
> Corporate Competence Center Embedded Linux

For what would you like to have code? The kconfig addition?

diff --git a/common/Kconfig.boot b/common/Kconfig.boot
index d3a12be228..a9ed4d4ec4 100644
--- a/common/Kconfig.boot
+++ b/common/Kconfig.boot
@@ -279,6 +279,14 @@ config SPL_FIT_GENERATOR
 endif # SPL
+	string "Public keys to use for FIT image verification"
+	help
+	  Public keys, or certificate files to extract them from, that shall
+	  be used to verify signed FIT images. The keys will be embedded into
+	  the control device tree of U-Boot.
 endif # FIT

But note that we are in a design discussion here, and I'm at least 
reluctant to code up n-versions without having some common idea where 
things should move.


Siemens AG, T RDA IOT
Corporate Competence Center Embedded Linux

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