RE: [PATCH v3 1/3] rpmb: add Replay Protected Memory Block (RPMB) subsystem

[Winkler, Tomas]

> 
> Hi Jens,
> 
> I realized there is one thing I wonder about:
> 
> On Tue, Feb 27, 2024 at 4:31 PM Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> 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 didn't quite get why these things are encoded big-endian?


By the spec.

> 
> As on the producer side (the eMMC backend) it seems we are anyway calling
> cpu_to_be* to convert them into this format.
> 
> If this is a requirement on the consumer side (such as TEE) I think the
> consumer should swap the bytes rather than the producer, but I guess that
> kind of assumes that we foresee there will be other consumers in the first
> place.
> 
This is end 2 end. 

> Yours,
> Linus Walleij