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

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Hi Jerome,

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

[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).

Thanks, but we may still need to address with multiple RPMB targets/regions in case of UFS/NVMe.

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 ?

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