I believe the reason this is being proposed is the transferal of secure storage (as opposed to protected storage) to an application root of trust partition. Such a partition
would still require access to the NV counters, at least as far as I know. We ran into this issue while creating the patch to do the transferal, and Jamie suggested this was the most sensible fix.
Raef
________________________________________
From: TF-M <tf-m-bounces@lists.trustedfirmware.org>
on behalf of Adrian Shaw via TF-M <tf-m@lists.trustedfirmware.org>
Sent: 22 January 2020 18:38
To: tf-m@lists.trustedfirmware.org;
Minos Galanakis
Cc: nd
Subject: Re: [TF-M] [Request For Comments] Expose the NV counters under platform service.
Hi Minos,
What are the use cases for Application Root of Trust services that need NV counters?
The NV counters are used by the PSA Root of Trust for rollback protection of images and secure storage. There are usually very few available. Hence the question above.
Adrian
________________________________
From: TF-M <tf-m-bounces@lists.trustedfirmware.org>
on behalf of Minos Galanakis via TF-M <tf-m@lists.trustedfirmware.org>
Sent: 22 January 2020 17:28
To: tf-m@lists.trustedfirmware.org <tf-m@lists.trustedfirmware.org>
Cc: nd <nd@arm.com>
Subject: [TF-M] [Request For Comments] Expose the NV counters under platform service.
Hi,
The Non-Volatile (NV) counters are a part of the PSA Root of Trust. In order to enable Applications residing in the Root of Trust partition to use the counters, an appropriate interface is needed.
This proposal is to enhance the existing platform service, in order to expose a generic API aimed at providing access to Non-Volatile counters to applications residing in the Application Root of Trust.
This implementation will not modify or affect the existing tfm_plat_nv_counters API or its’ platform specific implementation and will instead introduce a shim layer between a psa_call and the existing logic.
All input, question or comments are greatly appreciated.
Minos
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