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

[Sumit Garg]

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
> >>> 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] 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.

-Sumit

>
> --
> Jerome