Re: Locking for HW crypto accelerators

On Thu, 30 Aug 2018 at 15:39, Herbert Xu [off-list ref] wrote:

On Thu, Aug 30, 2018 at 02:22:22PM +0200, Krzysztof Kozlowski wrote:

quoted

Hi,

I am trying to figure out necessary locking on the driver side of
crypto HW accelerator for symmetric hash (actually: CRC). I
implemented quite simple driver for shash_alg.

I looked at the docs, I looked at the crypto kcapi core code... and
there is nothing about necessary locking. kcapi does not perform it.

My HW is quite similar to drivers/crypto/stm32/stm32_crc32.c so it has
only one HW set of registers for dealing with CRC. Or in other words,
only one queue of one element. :) I implemented all shash_alg
callbacks - init(), update(), final()... and also finup() (manually
calling update+final) and digest() (init+update+final).

Now imagine multiple user-space users of this crypto alg where all of
them call kcapi_md_digest() (so essentially init() -> update() ->
final()). It seems that kcapi does not perform any locking here so at
some point updates from different processes might be mixed with
finals:

Process A:             Process B:
init()
                       init()
update()
                       update()
final()
                       final()

My findings show that the requests are indeed being mixed with each other...

After each operation all state must be stored in the ahash_request
object.  The next operation should then load the state from the
request object into the hardware.

Thanks, that's the solution I was missing.

Best regards,
Krzysztof