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

On Thu, 26 Jun 2025 07:55:34 -0400 Daniel Zahka wrote:

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+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 think this is a requirement put forward in the spec?
Specifically if a device wants to allow partitioning of the SPI
space it may let the host pick the SPI. To me the device allocating 
the SPIs seemed more like a convenience thing that a security feature
to prevent reuse.

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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.