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

[Sumit Garg]

On Wed, 23 Aug 2023 at 13:34, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
>
> On Tue, Aug 22, 2023 at 9:07 PM Shyam Saini
> <shyamsaini@xxxxxxxxxxxxxxxxxxx> wrote:
>
> > 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 ?
>
> We don't break userspace. Just not. This is not an option.
>
> The RPMB subsystem simply has to provide the rpmb character
> device the same way the MMC subsystem did, or provide an
> in-kernel backend to the MMC subsystem so that it can provide
> the same device. Whatever solution is best.
>
> No deprecation and deletion and breaking userspace. Ever.
>

Agree, that's the golden rule of thumb we follow in kernel
development. Also, we still need to allow cases where trusted
provisioning user-space tools can program OP-TEE RPMB key during
factory provisioning. And once that is provisioned, I don't think
there is much harm in still exposing the RPMB device to user-space
since it can't do anything malicious without access to OP-TEE RPMB
key.

-Sumit

> Yours,
> Linus Walleij