On Mon, 21 Aug 2023 at 17:26, Ilias Apalodimas ilias.apalodimas@linaro.org wrote:
On Mon, 21 Aug 2023 at 14:19, 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 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 ?