Message-ID: <edaa7ae7-87f3-4566-b196-49c3ec97ed7d@gmail.com>
Date: Thu, 26 Jun 2025 07:55:34 -0400
From: Daniel Zahka <daniel.zahka@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Donald Hunter <donald.hunter@...il.com>, Jakub Kicinski <kuba@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 Jonathan Corbet <corbet@....net>, Andrew Lunn <andrew+netdev@...n.ch>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Tariq Toukan <tariqt@...dia.com>, Boris Pismenny <borisp@...dia.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, Willem de Bruijn
 <willemb@...gle.com>, David Ahern <dsahern@...nel.org>,
 Neal Cardwell <ncardwell@...gle.com>, Patrisious Haddad
 <phaddad@...dia.com>, Raed Salem <raeds@...dia.com>,
 Jianbo Liu <jianbol@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>,
 Rahul Rameshbabu <rrameshbabu@...dia.com>,
 Stanislav Fomichev <sdf@...ichev.me>,
 Toke Høiland-Jørgensen <toke@...hat.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Jacob Keller <jacob.e.keller@...el.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 01/17] psp: add documentation

On 6/25/25 7:42 PM, Willem de Bruijn wrote:
> Daniel Zahka wrote:
>> From: Jakub Kicinski <kuba@...nel.org>
>>
>> Add documentation of things which belong in the docs rather
>> than commit messages.
>>
>> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
>> Signed-off-by: Daniel Zahka <daniel.zahka@...il.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.

As it is now, psp-versions-ena is only used to affect the device 
configuration. So, the code for handling sockets i.e. 
psp_nl_rx_assoc_doit() / psp_nl_tx_assoc_doit() does not include a check 
against anything controlled by this setting. We only have a check 
against psp_dev->caps->versions, which is fixed after psp_dev_create(). 
Perhaps that would make sense though.

>> +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.
>

Indeed that last sentence is superfluous. Re-initializing a device 
shouldn't leave a device key from a previous initialization, while 
resetting the spi space. If something like that were possible, it should 
probably be obvious to the driver writer to do something like double 
rotate the keys.

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