[U-Boot] [RFC] efi_loader: EFI variables

[Heinrich Schuchardt]

On 2/12/19 10:49 AM, Alexander Graf wrote:
> On 02/03/2019 07:32 PM, Heinrich Schuchardt wrote:
>> Hello Alex, hello Takahiro,
>>
>> this morning I met Daniel Thompson of Linaro. He thinks it would be
>> quite valuable if U-Boot would at least offer read access to EFI
>> variables at runtime.
>>
>> I think what it takes is only a RAM buffer that we put between our
>> current storage backend (i.e. synchronization with U-Boot variables)
>> and the API implementation.
>>
>> We will need such a buffer anyway for non-permanent variables once we
>> have a SPI flash storage.
> 
> I think slowly we need to take a critical design decision: Do we want to
> be in the business of managing runtime UEFI variables?
> 
> I don't have a fully cohesive answer to that yet. My gut feeling tells
> me, that runtime variables would be much better off if they lived in
> TrustZone. That way we don't have to play relocation tricks, and devices
> that give you persistency are owned by the secure world anyway, so there
> is no weird intersection between OS and RTS.
> 
> So maybe the path forward would be to implement variable services in ATF
> (or OP-TEE rather I suppose) and just provide shim stubs to communicate
> with them from runtime services? That would keep all the variable logic
> platform agnostic, and we would not have to jump through weird hoops
> with DM.

U-Boot' major asset are the many boards supported by drivers. Does ATF
or OP-TEE have drivers for SPI?

Or is your idea that U-Boot would provide a module that is set up as a
trusted driver or trusted app, cf.
https://developer.arm.com/-/media/developer/Block%20Diagrams/Architecture-of-TEE%20copy.png

Best regards

Heinrich