[PATCH 0/2] RFC: add fdt_add_pubkey tool

[Jan Kiszka]

On 09.11.21 13:43, François Ozog wrote:
> Hi
> 
> as we are in design discussions, I would promote the idea of not pushing
> non hardware related things in the DTB that is passed to the kernel.

This was never proposed. The public keys go into the *control* FDTs.

> Is your use case to allow U-Boot to verify the kernel's signature ?
> Why not putting it into an environment variable?

This is both about validating OS FIT containers as well as SPL checking
U-Boot proper before continuing the boot there. The former case can be
replaced with UEFI logic and likely taking the key from TEE (we do that
as well in first prototypes), but the latter can't (yet).

> 
> If your use case is on Arm or RISC-V, both environments are working
> heavily to make https://arm-software.github.io/ebbr/
> <https://arm-software.github.io/ebbr/> standard available on a large
> number of boards.
> This offers UEFI interface and SecureBoot (and later MeasuredBoot)
> services. For Arm boards just check for SystemReady compliance.
> In this context, traditional UEFI secure variables are used to deal with
> certificates and hashes: PK, KEK, db...
> You can obviously do differently but you will be on your own to extend
> the chain of trust to IMA, secure containers (rooted down to hRoT) and
> other security facilities in the Linux side.
> Could you describe your use case in more details? 

doc/uImage.FIT/signature.txt ;)

More concrete: We are currently massaging board/siemens/iot2050 to close
its static chain of trust between SPL and U-Boot main, using software
means (vendor means do not work because FSBL key != TF-A/TEE/U-Boot key).

Jan

> 
> On Tue, 9 Nov 2021 at 11:07, Jan Kiszka <jan.kiszka at siemens.com
> <mailto: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
>     <mailto:jan.kiszka at siemens.com>>
>     > Sent: Tuesday, November 9, 2021 12:17 PM
>     > To: Roman Kopytin <Roman.Kopytin at kaspersky.com
>     <mailto:Roman.Kopytin at kaspersky.com>>; u-boot at lists.denx.de
>     <mailto:u-boot at lists.denx.de>; Rasmus Villemoes
>     <rasmus.villemoes at prevas.dk <mailto: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/
>     <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.
> 
>     Jan
> 
>     -- 
>     Siemens AG, T RDA IOT
>     Corporate Competence Center Embedded Linux
> 
> 
> 
> -- 
> 	
> François-Frédéric Ozog | /Director Business Development/
> T: +33.67221.6485
> francois.ozog at linaro.org <mailto:francois.ozog at linaro.org> | Skype: ffozog
> 
> 

-- 
Siemens AG, T RDA IOT
Corporate Competence Center Embedded Linux