Re: [RFC, PATCH 1/1] rpmb: add Replay Protected Memory Block (RPMB) driver

[Jerome Forissier <jerome.forissier@linaro.org>]

On 8/17/23 01:31, Shyam Saini wrote:
> 
> Hi Ulf,
> 
>> On Sat, 22 Jul 2023 at 03:41, Shyam Saini
>> <shyamsaini@linux.microsoft.com> wrote:
>>>
>>> From: Alex Bennée <alex.bennee@linaro.org>
>>>
>>> [This is patch 1 from [1] Alex's submission and this RPMB layer was
>>> originally proposed by [2]Thomas Winkler ]
>>>
>>> A number of storage technologies support a specialised hardware
>>> partition designed to be resistant to replay attacks. The underlying
>>> HW protocols differ but the operations are common. The RPMB partition
>>> cannot be accessed via standard block layer, but by a set of specific
>>> commands: WRITE, READ, GET_WRITE_COUNTER, and PROGRAM_KEY. Such a
>>> partition provides authenticated and replay protected access, hence
>>> suitable as a secure storage.
>>>
>>> The initial aim of this patch is to provide a simple RPMB Driver which
>>> can be accessed by Linux's optee driver to facilitate fast-path for
>>> RPMB access to optee OS(secure OS) during the boot time. [1] Currently,
>>> Optee OS relies on user-tee supplicant to access eMMC RPMB partition.
>>>
>>> A TEE device driver can claim the RPMB interface, for example, via
>>> class_interface_register(). The RPMB driver provides a series of
>>> operations for interacting with the device.
>>
>> I don't quite follow this. More exactly, how will the TEE driver know
>> what RPMB device it should use?
> 
> I don't have complete code to for this yet, but i think OP-TEE driver
> should register with RPMB subsystem and then we can have eMMC/UFS/NVMe
> specific implementation for RPMB operations.
> 
> Linux optee driver can handle RPMB frames and pass it to RPMB subsystem
> 
> [1] U-Boot has mmc specific implementation
> 
> I think OPTEE-OS has CFG_RPMB_FS_DEV_ID option
> CFG_RPMB_FS_DEV_ID=1 for /dev/mmcblk1rpmb,

Correct. Note that tee-supplicant will ignore this device ID if --rmb-cid
is given and use the specified RPMB instead (the CID is a non-ambiguous way
to identify a RPMB device).

> but in case if a
> system has multiple RPMB devices such as UFS/eMMC/NVMe, one them
> should be declared as secure storage and optee should access that one only.

Indeed, that would be an equivalent of tee-supplicant's --rpmb-cid.

> Sumit, do you have suggestions for this ?


-- 
Jerome