linux-kernel - Re: Locking for HW crypto accelerators

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Date:   Thu, 30 Aug 2018 15:19:09 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Locking for HW crypto accelerators

Am Donnerstag, 30. August 2018, 15:09:05 CEST schrieb Krzysztof Kozlowski:

Hi Krzysztof,

> Thanks Stephan for hints. Let's assume the each of init, update and
> final are atomic... but how about the relation between update and
> final? I have two concurrent users in user-space but only one HW:
> 
> Process A:             Process B:
> init() and set_key()
>                        init() and different key
> update(some_data)
>                        update(different_data)
> final()
>                        final()
> 
> The final() from process A will now produce the result of hashing/CRC
> of some_data and different_data (and even maybe mixed with init() for
> different key). All because in the meantime process B added its own
> data to the HW.

The question is where is the state of the cipher operation kept that is 
produced with each of the init/update/final calls. Your answer implies that 
this state is kept in hardware.

But commonly the state is kept in software. Look at ahash_request for example, 
the __ctx pointer is intended to point to the memory the driver needs to store 
its state.

Pick a random driver implementation and search for ahash_request_ctx, for 
example.
> 
> Best regards,
> Krzysztof



Ciao
Stephan