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

[Linus Walleij]

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?

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.

Yours,
Linus Walleij