linux-kernel - Re: [PATCH v3 1/3] rpmb: add Replay Protected Memory Block (RPMB) subsystem

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Date: Mon, 25 Mar 2024 14:44:13 +0100
From: Jens Wiklander <jens.wiklander@...aro.org>
To: "Winkler, Tomas" <tomas.winkler@...el.com>
Cc: Avri Altman <Avri.Altman@....com>, Ulf Hansson <ulf.hansson@...aro.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>, 
	"op-tee@...ts.trustedfirmware.org" <op-tee@...ts.trustedfirmware.org>, 
	Shyam Saini <shyamsaini@...ux.microsoft.com>, 
	Jerome Forissier <jerome.forissier@...aro.org>, Sumit Garg <sumit.garg@...aro.org>, 
	Ilias Apalodimas <ilias.apalodimas@...aro.org>, Bart Van Assche <bvanassche@....org>, 
	Randy Dunlap <rdunlap@...radead.org>, Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alex Bennée <alex.bennee@...aro.org>
Subject: Re: [PATCH v3 1/3] rpmb: add Replay Protected Memory Block (RPMB) subsystem

On Mon, Mar 25, 2024 at 9:23 AM Winkler, Tomas <tomas.winkler@...elcom> wrote:
>
>
> > > > +struct rpmb_frame {
> > > > +       u8     stuff[196];
> > > > +       u8     key_mac[32];
> > > > +       u8     data[256];
> > > > +       u8     nonce[16];
> > > > +       __be32 write_counter;
> > > > +       __be16 addr;
> > > > +       __be16 block_count;
> > > > +       __be16 result;
> > > > +       __be16 req_resp;
> > > > +} __packed;
> > >
> > > I haven't looked at the NVME or the UFS spec in detail. Although, I
> > > assume the above frame makes sense for those types of
> > interfaces/protocols too?
> > The rpmb implementation in ufs, has drifted apart from eMMC. E.g. in
> > UFS4.0:
> >  -  the frame is different - see struct ufs_arpmb_meta in
> > include/uapi/scsi/scsi_bsg_ufs.h,
> >  - Additional extended header was added,
> >  - the frame size is no longer 512Bytes (256Bytes meta info + 256Bytes data)
> > but 4k,
> >  - there are 9 rpmb operations instead of 7,
> >  - The atomicity requirement of the command sequence was waved, And
> > probably more differences that I forgot.
> > This is why it is better to designated this as an eMMC-only implementation?

Thanks for the update.

To move forward here we can either
1. as you suggest make this an eMMC-only implementation,
or
2. we could remove struct rpmb_frame from include/linux/rpmb.h to make
the shuffled data more opaque.

Is it possible to find and route RPMB data to NVME and UFS devices
without a common meeting point like the RPMB subsystem proposed here?
If the answer is yes option 1 makes more sense since we'll add a
missing capability to eMMC. If the answer is no option 2 makes sense
for NVME and UFS even if we save the implementation for later.

>
> As  I wrote previously the original implementation has already resolved protocol differences
>  (NVMe have also different byte ordering) for closed usecase of storing data (not the configuration)
> I believe the whole point here is to let TEE driver to store the data, regardless of the technology.

Agreed.

>  In addition I might be wrong but I don't see much value in eMMC as the UFS and NVMe are currently leading technologies.

This patchset addresses a problem on present platforms so it's not irrelevant.

Thanks,
Jens