[U-Boot] [EXT] Re: [PATCH 4/6] spl: mmc: support loading i.MX container format file

[Peng Fan]

> Subject: Re: [EXT] Re: [U-Boot] [PATCH 4/6] spl: mmc: support loading i.MX
> container format file
> 
> On 5/30/19 9:06 AM, Ye Li wrote:
> > On 2019/5/27 19:31, Marek Vasut wrote:
> >> Caution: EXT Email
> >>
> >> On 5/27/19 11:49 AM, Peng Fan wrote:
> >>> Hi Marek, Lukasz,
> >>>
> >>>> Subject: Re: [EXT] Re: [U-Boot] [PATCH 4/6] spl: mmc: support
> >>>> loading i.MX container format file
> >>>>
> >>>> Hi Marek,
> >>>>
> >>>> On 2019/5/22 19:41, Marek Vasut wrote:
> >>>>> Caution: EXT Email
> >>>>>
> >>>>> On 5/22/19 9:34 AM, Lukasz Majewski wrote:
> >>>>> [...]
> >>>>>>>>>>>> By using above approach we do have the NXP's "container"
> >>>>>>>>>>>> format only seen in the SPL (which is OK, as for example
> >>>>>>>>>>>> Samsung does similar thing with FBL/BL1). When SPL is
> "trused"
> >>>>>>>>>>>> we may use available facilities.
> >>>>>>>>>>>
> >>>>>>>>>>> The issue to me is that sc_seco_authenticate could not take
> >>>>>>>>>>> a FIT image as input.
> >>>>>>>>>>
> >>>>>>>>>> Is the sc_seco_authenticate an API accessible from SPL,
> >>>>>>>>>> U-Boot proper or Linux crypro engine driver?
> >>>>>>>>>
> >>>>>>>>> Yes, it is an API accessible in SPL/U-Boot stage. I do not
> >>>>>>>>> know about Linux crypto driver.
> >>>>>>>>
> >>>>>>>> Maybe it would be worth to check how Linux handle this? Maybe
> >>>>>>>> it would shed some more light on it?
> >>>>>>>
> >>>>>>> I am not familiar with that, so might be stupid question below.
> >>>>>>> Does it really matter?
> >>>>>>
> >>>>>> I would check it just out of curiosity.
> >>>>>
> >>>>> Yes, it matters, because there should be such API. How would Linux
> >>>>> authenticate e.g. userspace binaries if there wasn't one, surely
> >>>>> not by wrapping every single object into the custom vendor-specific
> container ?
> >>>>> And if there is one, you can use it to authenticate raw binaries
> >>>>> from U-Boot SPL too, e.g. fitImage blobs with an associated signature.
> >>>>>
> >>>>
> >>>> iMX8 AHAB uses RSA key pair for authentication, the on-chip thing
> >>>> we called SRK is a array of public key hash which is dedicated for
> >>>> AHAB. It is not a real key. The real public key is in container.
> >>>> AHAB will check the public key with the on-chip SRK before using it
> >>>> to authenticate the image.
> >>>> Seco which contains the crypto engine on imx8 does not allow to use
> >>>> the SRK by user. No such API exported.
> >>>> And the fuse of SRK is locked, can't be read directly.
> >>>>
> >>>> Actually on imx6/imx7/imx8m, the SPL and u-boot are already using
> >>>> ROM HAB to implement the trust chain, like SPL authenticates
> >>>> u-boot, u-boot authenticatse kernel. We just follow this same way
> >>>> on imx8, the difference is
> >>>> imx8 needs container format for signed image. We prefer directly
> >>>> loading container image than fit image.
> >>>> If we pack fit image into container, obviously this will cause one more
> copy.
> >>>> As a boot loader, isn't it better to have more image format supported?
> >>
> >> If the functionality of the new image format is a subset of already
> >> present image format, then no, that's called a duplication.
> >>
> >>>> We
> >>>> don't force to use container, just set it as default. Users still
> >>>> can choose fit or raw image.
> >>
> >> They can. however they cannot authenticate the fitImage because the
> >> firmware doesn't provide the necessary API for that ?
> >>
> >>>
> >>> Do you have more comment?
> >>
> >> How could Linux use this iMX8 chain of trust stuff to authenticate e.g.
> >> userspace binaries ? It's the same thing as authenticating blob in a
> >> fitImage.
> >>
> >
> > Userspace binaries don't use the same key pair. They are signed by
> > software vendors' key. The private key for chip secure boot is only hold by
> device manufacturer.
> > For example, android needs to authenticate a signed APK. Its public key (Key
> A) is in system FS.
> > iMX trust chain only reaches to kernel + ramdisk. Then the chain hands over
> to android.
> > In ramdisk, android puts another public Key (Key B) used by dm-verify
> > for system FS. So once system FS is verified ok, then the public key A
> > becomes trusted. Finally we can use public key A for APK authentication.
> 
> So can we put a public key into the SPL and use it to verify a fitImage ?

Technically doable. But compared with the current approach that reuse
ROM public API, Using crypto driver in SPL will be complicated and code
size larger without calling ROM API.

I do not understand the problem the SPL loading NXP i.MX8 container format.
SPL should only support raw and fit format? vendor format is not
allowed and not accepted?

Stefano, Simon, Tom

Any comments?

Thanks,
Peng.

> 
> --
> Best regards,
> Marek Vasut