[PATCH 0/2] RFC: add fdt_add_pubkey tool

[Simon Glass]

Hi Jan,

On Tue, 9 Nov 2021 at 03:07, Jan Kiszka <jan.kiszka at siemens.com> wrote:
>
> 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
>
> +config FIT_SIGNATURE_PUB_KEYS
> +       string "Public keys to use for FIT image verification"
> +       depends on FIT_SIGNATURE || SPL_FIT_SIGNATURE
> +       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
>
>  config LEGACY_IMAGE_FORMAT
>
>
> 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.

I'm not sure we want this built into U-Boot. I see signing of a
firmware image as a final step, with the keys being added then, e.g.
by binman.

Regards,
Simon