linux-kernel - Re: [RFC PATCH 1/5] rpmb: add Replay Protected Memory Block (RPMB) subsystem

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Message-ID: <CACRpkdZb5UMyq5qSJE==3ZnH-7fh92q_t4AnE8mPm0oFEJxqpQ@mail.gmail.com>
Date:   Thu, 11 Mar 2021 01:49:08 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     Hector Martin <marcan@...can.st>, Arnd Bergmann <arnd@...aro.org>,
        "open list:ASYMMETRIC KEYS" <keyrings@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Joakim Bech <joakim.bech@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Maxim Uvarov <maxim.uvarov@...aro.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Ruchika Gupta <ruchika.gupta@...aro.org>,
        "Winkler, Tomas" <tomas.winkler@...el.com>, yang.huang@...el.com,
        bing.zhu@...el.com, Matti.Moell@...nsynergy.com,
        hmo@...nsynergy.com, linux-mmc <linux-mmc@...r.kernel.org>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        linux-nvme@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>,
        Arnd Bergmann <arnd.bergmann@...aro.org>
Subject: Re: [RFC PATCH 1/5] rpmb: add Replay Protected Memory Block (RPMB) subsystem

On Wed, Mar 10, 2021 at 11:29 AM Sumit Garg <sumit.garg@...aro.org> wrote:

> And RPMB key provisioning
> being a one time process should be carried out carefully during device
> manufacturing only.

For a product use case such as a mobile or chromebook or
set-top box: yes. In this scenario something like TEE possesses
this symmetric key.

But for a random laptop with an NVME containing an RPMB it
may be something the user want to initialize and use to lock down
their machine.

The use case for TPM on laptops is similar: it can be used by a
provider to lock down a machine, but it can also be used by the
random user to store keys. Very few users beside James
Bottomley are capable of doing that (I am not) but they exist.
https://blog.hansenpartnership.com/using-your-tpm-as-a-secure-key-store/

I think we need to think not only of existing use cases but also
possible ones even if there is currently no software for other
use cases. (But maybe that is too ambitious.)

Yours,
Linus Walleij