On Mon, 21 Aug 2023 at 16:49, Jens Wiklander jens.wiklander@linaro.org wrote:
On Mon, Aug 21, 2023 at 12:03 PM Sumit Garg sumit.garg@linaro.org wrote:
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.
+1
[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 would require intercepting OP-TEE RPMB frames such that any "write key" frame is blocked. As we don't want OP-TEE to occupy unprovisioned RPMB partitions.
That should avoid the problem of provisioning a device-unique secure DTB.
Okay I see the scalability concerns. So how about instead we have a UFS/eMMC/NVMe controller specific boolean secure RPMB DT property?
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.
Agree but any such RPMB key provisioning tool should either belong to OP-TEE, u-boot or Linux.
-Sumit
Cheers, Jens
-Sumit
-- Jerome