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

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Hi Sumit,

On Mon, 21 Aug 2023 at 15:19, Jerome Forissier
<jerome.forissier@xxxxxxxxxx> wrote:

On 8/17/23 01:31, Shyam Saini wrote:

Hi Ulf,

On Sat, 22 Jul 2023 at 03:41, Shyam Saini
<shyamsaini@xxxxxxxxxxxxxxxxxxx> wrote:

From: Alex Bennée <alex.bennee@xxxxxxxxxx>

[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
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] 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.



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