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

Wed May 22 06:46:22 UTC 2019

Hi Peng,

> > > > > > Subject: Re: [U-Boot] [PATCH 4/6] spl: mmc: support loading
> > > > > > i.MX container format file
> > > > > >
> > > > > > On 5/21/19 4:55 AM, Peng Fan wrote:
> > > > > > [...]
> > > > > >  
> > > > > > >>>>> I do not know how other SoC vendor did FIT hardware
> > > > > > >>>>> secure boot, please share you have any information.  
> > > > > > >>>>
> > > > > > >>>> The SPL can be in the custom format, but then can load
> > > > > > >>>> fitImage with the next stage(s), right ?  
> > > > > > >>>
> > > > > > >>> I am not able to follow you, could you share more
> > > > > > >>> details?  
> > > > > > >>
> > > > > > >> Wrap the SPL into this custom format and then have the
> > > > > > >> SPL load/authenticate fitImage with the rest (U-Boot,
> > > > > > >> Linux, DTB etc). Would that work ?  
> > > > > > >
> > > > > > > It not work.
> > > > > > > We already wrap SPL in i.MX container format, this
> > > > > > > patchset is to let SPL could load the 2nd container file
> > > > > > > which contains U-Boot/DTB/OP-TEE/ATF.  If we let SPL load
> > > > > > > a fitimage which contains (U-Boot/DTB and etc), it could
> > > > > > > not pass secure boot authentication, because ROM not know
> > > > > > > fitimage, it only know i.MX container format.  
> > > > > >
> > > > > > It's not bootrom that authenticates the next stage, it's
> > > > > > U-Boot SPL. BootROM already authenticated and started the
> > > > > > U-Boot SPL, so that's a trusted code. Now this trusted code
> > > > > > can authenticate and start the next stage (U-Boot, ATF,
> > > > > > OpTee OS, etc) ; the BootROM is already out of the picture
> > > > > > at this point.  
> > > > >
> > > > > Sorry for not clear. On i.MX8, SCFW (a runtime firmware
> > > > > )exports API for others to use, sc_seco_authenticate is the
> > > > > API that used for authentication. I could not share more
> > > > > information about this API works inside SCFW and ROM. sc_err_t
> > > > > sc_seco_authenticate(sc_ipc_t ipc, sc_seco_auth_cmd_t cmd,
> > > > > sc_faddr_t addr)
> > > > >
> > > > > SPL will call this API, one parameter is address which needs a
> > > > > container image there.  
> > > >
> > > > Please consider following scenario (I think that this is in sync
> > > > with Marek's point):
> > > >
> > > > 1. You wrap SPL into i.MX8 "container", so the SPL would be
> > > > recognised an checked by secure code in ROM.
> > > >
> > > > 2. Then we do have SPL "trusted". It is up to SPL to:
> > > >
> > > > 2.1. Use its private key to check u-boot, dtb, etc embedded into
> > > > FitImage (as written here: ./doc/uImage.FIT/verified-boot.txt).
> > > >
> > > > 2.2. Use crypto engine (it's API) with fused keys to speed-up
> > > > the process of boot (by HW support to check the binary). Such
> > > > approach is in i.MX6Q.  
> > >
> > > I suppose you talking HAB.  
> > 
> > Yes. As described here:
> > 
> > https://www.nxp.com/docs/en/application-note/AN4581.pdf
> >   
> > >  
> > > >
> > > >
> > > > 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?

> 
> > 
> > Or is it just the function executed by ROM on the very beginning to
> > load SPL? 
> > >
> > > If I switch to FIT, I need to use FIT to wrap a container image,
> > > it does not make sense to me.  
> > 
> > Please correct me if I'm wrong, but isn't the container image only
> > needed to wrap SPL?  
> 
> Container image will wrap SPL to make ROM could load SPL, Kick SPL and
> authenticate SPL.

Ok. So it is needed in the ROM "part" of security.

> 
> When SPL booting U-Boot, SPL could use FIT to load and boot uboot.
> But when SPL need to authenticate U-Boot with AHAB on i.MX8, a
> container format header/image needs to be passed to
> sc_seco_authenticate API, the API internal implementation is it will
> parse the container header/image.

Ok. So every time we want to use the sc_seco_authenticate API the
provided image for checking needs to be wrapped into the "container"
iMX8 specific format.

> 
> So in vendor tree, uboot/atf/optee are wrapped into a container
> format image.

Ok.

> 
> > 
> > In which other cases the container image is needed in U-Boot proper
> > or Linux kernel?  
> 
> When uboot authenticate kernel, we also wrap kernel image into a
> container format file using CST. I do not know how Linux kernel
> itself authenticate others.
> 
> Thanks,
> Peng.
> 
> >   
> > >
> > > Thanks,
> > > Peng.  
> > > >  
> > > > >  
> > > > > >  
> > > > > > > For authentication, we always let ROM to authenticate
> > > > > > > including SPL authenticating U-Boot, so we need pass an
> > > > > > > image to ROM that ROM could recognize when SPL booting
> > > > > > > 2nd image.  
> > > > > >
> > > > > > Shouldn't the CPU have some sort of facility, like a crypto
> > > > > > engine, which authenticates whatever blob with the right
> > > > > > signature against a key burned into the CPU ? If so, then
> > > > > > you would just implement a crypto driver and pass the blob
> > > > > > and signature to it. I suspect that's how it should work,
> > > > > > how else would Linux be able to make use of these secure
> > > > > > bits if it cannot call the bootrom anymore ?  
> > > > >
> > > > > sc_seco_authenticate on i.MX8 will always be available. It is
> > > > > exported by a runtime firmware running on a Cortex-M core
> > > > > inside i.MX8. The API will do authentication, its accepts
> > > > > container format image as input and no other format.
> > > > >
> > > > > Thanks,
> > > > > Peng.
> > > > >  
> > > > > >
> > > > > > --
> > > > > > Best regards,
> > > > > > Marek Vasut  
> > > > > _______________________________________________
> > > > > U-Boot mailing list
> > > > > U-Boot at lists.denx.de
> > > > > https://lists.denx.de/listinfo/u-boot  
> > > >
> > > >
> > > >
> > > >
> > > > Best regards,
> > > >
> > > > Lukasz Majewski
> > > >
> > > > --
> > > >
> > > > DENX Software Engineering GmbH,      Managing Director: Wolfgang
> > > > Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194
> > > > Groebenzell, Germany Phone: (+49)-8142-66989-59 Fax:
> > > > (+49)-8142-66989-80 Email: lukma at denx.de  
> > 
> > 
> > 
> > 
> > Best regards,
> > 
> > Lukasz Majewski
> > 
> > --
> > 
> > DENX Software Engineering GmbH,      Managing Director: Wolfgang
> > Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell,
> > Germany Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email:
> > lukma at denx.de  

Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma at denx.de
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