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

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On Mon, 21 Aug 2023 at 17:26, Ilias Apalodimas
<ilias.apalodimas@xxxxxxxxxx> wrote:

On Mon, 21 Aug 2023 at 14:19, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:

On Mon, Aug 21, 2023 at 12:03 PM Sumit Garg <sumit.garg@xxxxxxxxxx> wrote:

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.


[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.

Another option is for OP-TEE to iterate over all RPMBs with a
programmed key and test if the key OP-TEE would use works. That should
avoid the problem of provisioning a device-unique secure DTB. I'd
expect that the RPMB key is programmed by a trusted provisioning tool
since allowing OP-TEE to program the RPMB key has never been secure,
not unless the OP-TEE binary is rollback protected.

+1 to that.  Overall we shound't 'trust' to do the programming. For
example, in OP-TEE if you compile it with device programming
capabilities, you can easily convince OP-TEE to send you the symmetric
key by swapping the supplicant with a malicious application.

Agree, with your overall intent, that OP-TEE shouldn't expose RPMB key
in plain form. But with suggested OP-TEE RPMB frames routing via
kernel, tee-supplicant won't be used for RPMB accesses.

do we plan to disable access to RPMB devices, once we have this RPMB driver in place. User space tools like mmc-utils/nvme/ufs utils
can still access RPMB and programme the key and should
RPMB driver deny access to RPMB ?

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