[U-Boot] [U-Boot, 1/2, v4] powerpc/mpc85xx: SECURE BOOT- NAND secure boot target for P3041

aneesh.bansal at freescale.com
2015-03-10T17:52:40Z

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, March 10, 2015 10:34 PM
> To: Bansal Aneesh-B39320
> Cc: u-boot at lists.denx.de; Sun York-R58495; Gupta Ruchika-R66431;
> Kushwaha Prabhakar-B32579
> Subject: Re: [U-Boot, 1/2, v4] powerpc/mpc85xx: SECURE BOOT- NAND
> secure boot target for P3041
>
> On Tue, 2015-03-10 at 03:50 -0500, Bansal Aneesh-B39320 wrote:
> > > -----Original Message-----
> > > From: Wood Scott-B07421
> > > Sent: Thursday, March 05, 2015 10:38 PM
> > > To: Bansal Aneesh-B39320
> > > Cc: u-boot at lists.denx.de; Sun York-R58495; Gupta Ruchika-R66431
> > > Subject: Re: [U-Boot, 1/2, v4] powerpc/mpc85xx: SECURE BOOT- NAND
> > > secure boot target for P3041
> > >
> > > On Thu, 2015-03-05 at 01:26 -0600, Bansal Aneesh-B39320 wrote:
> > > > > -----Original Message-----
> > > > > From: Wood Scott-B07421
> > > > > Sent: Thursday, March 05, 2015 2:41 AM
> > > > > To: Bansal Aneesh-B39320
> > > > > Cc: u-boot at lists.denx.de; Sun York-R58495; Gupta Ruchika-R66431
> > > > > Subject: Re: [U-Boot, 1/2, v4] powerpc/mpc85xx: SECURE BOOT-
> > > > > NAND secure boot target for P3041
> > > > >
> > > > > Where does the 3.5G limitation come from? Even if the physical
> > > > > address needs to be elsewhere due to bootrom constraints, we
> > > > > should be able to map it wherever we want in the TLB once U-Boot
> > > > > takes
> > > control.
> > > > >
> > > > The 3.5G limitation comes from BootROM in case of secure Boot.
> > > > Initially U-Boot has to run from CPC configured as SRAM with
> > > > address Within 3.5G. Once U-boot has relocated to DDR, we have
> > > > removed the Corresponding TLB entry.
> > >
> > > Again, you could relocate the virtual address of L3 much earlier.
> > >
> > > -Scott
> > >
> > Are you suggesting the following:
> > 1. PBI Commands to configure CPC as SRAM with address 0xBFF0_0000.
> > 2. Compile U-boot with TEXT BASE as 0xFFF40000.
> > 3. Copy the U-boot from NAND via PBI commands to CPC (SRAM) on
> > address 0xBFF4_0000 4. The BootROM will validate the U-boot and transfer
> the control to 0xBFFF_FFFC.
> > 5. When U-boot is executing, then in the last 4K code, when shifting from
> AS=0 to AS=1,
> > we change the address of SRAM from 0xBFF0_0000 to 0xFFF0_0000.
> > (Similar to what is done for NOR Boot)
>
> Something like that, except in step 5 it would only be changing the virtual
> address, not the physical address (unless you can do a similar trick as NOR
> does, to have the L3 cache repeat and cover both addresses at once).
>
> -Scott
>
The problems that I see here are:
1. Can SRAM address be changed without disabling and re-configuring CPC as SRAM ?
2. Assuming that above is possible,

We are executing from CPC configured as SRAM with address as 0xBFF0_0000. (Because of 3.5 G Limitation)
We create a LAW for 0xFFF0_0000 to map to CPC and
change the address of SRAM in CPC controller from BFF0_0000 to 0xFFF0_0000. (If it is possible... need to check this)
But now the Code which was executing is executing from 0xBFFx_xxxx. So the CPC controller will reject this since configured address for SRAM is different.
NOR can have two addresses as IFC controller ignores the upper bit but this is not possible with CPC.

To avoid this, even if we create a TLB Entry to map the virtual address 0xBFFx_xxxx to 0xFFFx_xxxx, then we have a race condition. Which step to do first?
Creation of TLB entry or changing the address of SRAM in CPC controller.
Because the current execution PC is 0xBFFx_xxxx (CPC as SRAM)

-Aneesh