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

[Shyam Saini <shyamsaini@linux.microsoft.com>]

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Hi Sumit,

> On Mon, 21 Aug 2023 at 15:19, Jerome Forissier
> <jerome.forissier@linaro.org> wrote:
>>
>>
>>
>> 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
>>>
>
> It would be better to have this OP-TEE use case fully implemented. So
> that we can justify it as a valid user for this proposed RPMB
> subsystem. If you are looking for any further suggestions then please
> let us know.

I was looking into UFS/NVMe user-space utils, it seems we may have to 
adapt rpmb frame data structure in optee-os to to handle NVMe/UFS
specific bits.

For nvme rpmb data frame, I think we would need an extra "target" member 
in rpmb data frame structure,
as NVMe can support upto 7 RPMB units, see  [1] "struct rpmb_data_frame_t"
UFS may support upto 3 or 4 RPMB regions.

So even if we use CID to uniquely identify RPMB device either from 
eMMC/NVMe/UFS, we still need identify which RPMB target/unit in case
if the device is NVMe, and which RPMB region if the device UFS.

Also both NVMe/UFS utils have two extra RPMB operations implemented,
Although new request/response operation than eMMC spec:
  1) Authenticated Device Configuration Block Write
  2) Authenticated Device Configuration Block Read

see [2] enum rpmb_request/response_type and [3]enum rpmb_op_type

do we need those implemented as well ?

Please let me know what you think about these.

[1] https://github.com/linux-nvme/nvme-cli/blob/master/nvme-rpmb.c#L252
[2] https://github.com/linux-nvme/nvme-cli/blob/master/nvme-rpmb.c#L230
[3] https://github.com/westerndigitalcorporation/ufs-utils/blob/dev/ufs_rpmb.c#L27

>>> [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 ?
>>
>
> I would suggest having an OP-TEE secure DT property that would provide
> the RPMB CID which is allocated to the secure world.
>
> -Sumit
>
>>
>> --
>> Jerome
>