Hi Everyone,
During our investigation into the slow write operations of the PSA Protected Storage (PS) API, we identified that numerous (>10) flash erase calls occur when executing psa_ps_set() or psa_ps_remove(). A significant portion of these erase calls is linked to the rollback protection mechanism, specifically for updating Non-Volatile (NV) counters.
A potential improvement we are considering is to differentiate rollback protection requirements based on the type of flash memory being used.
* For systems utilizing internal flash, we suggest possibility to disable rollback protection when encryption is enabled. This improves speed of write and remove operations and reduces the flash wear. * Rollback protection should be enabled when protected storage is located in external flash to ensure data integrity and security
Currently, there is a Kconfig option, CONFIG_TFM_PS_ROLLBACK_PROTECTION, to disable rollback protection. However, a build-time check requires that PS encryption is also disabled, as referenced here: https://git.trustedfirmware.org/plugins/gitiles/TF-M/trusted-firmware-m.git/...
To better align rollback protection with the type of flash memory, there is the possibility of updating the macro rule. This could involve either removing the existing rollback protection check or adding a new rule based on the flash type, enforcing rollback protection only for external flash. While introducing a Kconfig option for the flash memory type is a potential solution, it raises concerns about reduced security in cases of misconfiguration. Your insights on how to address this would be invaluable. Thank you in advance for your input! Best regards, Juha Ylinen