Re: [PATCH v2 01/17] psp: add documentation

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Daniel Zahka wrote:
> From: Jakub Kicinski <kuba@kernel.org>
> 
> Add documentation of things which belong in the docs rather
> than commit messages.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>

> +Driver notes
> +------------
> +
> +Drivers are expected to start with no PSP enabled (``psp-versions-ena``
> +in ``dev-get`` set to ``0``) whenever possible. The user space should
> +not depend on this behavior, as future extension may necessitate creation
> +of devices with PSP already enabled, nonetheless drivers should not enable
> +PSP by default. Enabling PSP should be the responsibility of the system
> +component which also takes care of key rotation.
> +
> +Note that ``psp-versions-ena`` is expected to be used only for enabling
> +receive processing. The device is not expected to reject transmit requests

This means skb encryption for already established connections only,
right? Establishing tx offload will be rejected for new connections.

> +after ``psp-versions-ena`` has been disabled. User may also disable
> +``psp-versions-ena`` while there are active associations, which will
> +break all PSP Rx processing.
> +
> +Drivers are expected to ensure that device key is usable upon init
> +(working keys can be allocated), and that no duplicate keys may be generated
> +(reuse of SPI without key rotation). Drivers may achieve this by rotating
> +keys twice before registering the PSP device.

Since the device returns a { session_key, spi } pair, risk of reuse
is purely in firmware. I don't follow the need for the extra double
rotation.