Fit Signature booting without public key

[Manorit Chawdhry]

Hi Tom,

On 10:05-20230525, Tom Rini wrote:
> On Thu, May 25, 2023 at 11:21:44AM +0530, Manorit Chawdhry wrote:
> > Hi Tom,
> > 
> > On 11:30-20230516, Tom Rini wrote:
> > > On Tue, May 16, 2023 at 12:11:24PM +0530, Manorit Chawdhry wrote:
> > > 
> > > > Hi All,
> > > > 
> > > > I recently came upon a discussion that had happened a while back [0].
> > > > I want to continue the discussion as I believe the issue still persists
> > > > and the checks around fit signature booting are still the same, that
> > > > allows booting the fit without changing the uboot dtb.
> > > > 
> > > > Allowing the signed fit image without this seems to be a bypass that is
> > > > available and should not be allowed without any gate to it for people
> > > > who'd like to enforce these signing checks. Let me know if there is a
> > > > config already available for it and if not, are there any plans to
> > > > enable such a config in future. Would like to hear your opinions on
> > > > this as I believe this should be fixed as soon as possible.
> > > > 
> > > > [0]: https://u-boot.denx.narkive.com/dEClg9dW/signed-fit-image-boots-without-public-key
> > > 
> > > Yes, can you please reproduce the issue in question on the current tree,
> > > with a supported platform and provide the defconfig and steps you used
> > > for this issue? Thanks.
> > > 
> > > -- 
> > 
> > I've created a branch with some custom patches to make the fitimage
> > booting currently, please try with the branch and the fitimage that are
> > also committed [0].
> > 
> > The devices that I've tested this with is j721e-hs-evm, the defconfig to
> > use for the builds are j721e_evm_r5_defconfig and
> > j721e_evm_a72_defconfig. Although not synced up with the latest changes
> > but for reference the SDK documentation can help if required [1].
> > 
> > Attached the logs for reference with the signed fitimage and an unsigned
> > uboot without any modifications[2].
> > 
> > [0]: https://github.com/manorit2001/u-boot/tree/fit-image-poc
> > [1]: https://software-dl.ti.com/jacinto7/esd/processor-sdk-linux-jacinto7/08_06_00_11/exports/docs/linux/Foundational_Components/U-Boot/UG-General-Info.html
> > [2]: https://gist.github.com/manorit2001/3c49cfc19bf937783efb75fd4cddc58f
> 
> I don't see the problem there, but please go and investigate what
> problem you're seeing.  The intention is that yes, with the appropriate
> CONFIG settings, you can set U-Boot to only boot signed FIT
> configurations and unsigned ones should not boot.
> 

It boots with an unsigned fit too btw for reference [0]. The whole
logic behind the authentication is that uboot stores the public key that
is used for verification of the signed fit but apparantely if I haven't
kept the public key in uboot dtb the fit images still boot whether
signed or unsigned as that check is not guarded by anything if you see
in the codebase[1].

[0]: https://gist.github.com/manorit2001/80c9242641141ac5bce0e335ea8a9f1a
[1]: https://github.com/u-boot/u-boot/blob/6dcee70692601bd3296c86ac07d0317bf06d2b7b/boot/image-fit-sig.c#L491-L496

Regards,
Manorit

> -- 
> Tom