linux-kernel - Re: [PATCH 16/18] crypto: talitos - do hw_context DMA mapping outside the requests

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Message-ID: <VI1PR0402MB3342B99A1BEA5622F29F79EF98CF0@VI1PR0402MB3342.eurprd04.prod.outlook.com>
Date:   Tue, 20 Feb 2018 11:32:25 +0000
From:   Horia Geantă <horia.geanta@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
CC:     Christophe LEROY <christophe.leroy@....fr>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 16/18] crypto: talitos - do hw_context DMA mapping outside
 the requests

On 2/20/2018 12:34 PM, Herbert Xu wrote:
> On Mon, Feb 19, 2018 at 01:16:30PM +0000, Horia Geantă wrote:
>>
>>> And what about ALGIF path from user space ?
>>> What if the user never calls the last sendmsg() which will call 
>>> hash_finup() ?
>>>
>> User is expected to follow the rules of the crypto API.
>> Of course, kernel won't (or at least shouldn't) crash in case of misuse.
>> However, in these cases some resources might not be freed - it's unavoidable.
> 
> the crypto API does not require the presence of a finalisation.
> It is entirely optional.  So leaving resources pinned down until
> final/finup occurs is unacceptable, both from user-space and the
> kernel.
> 
If final/finup is optional, how is the final hash supposed to be retrieved?

According to documentation, these are the accepted flows (with the option to
export/import a partial hash b/w update and final/finup):

.init() -> .update() -> .final()
            ^    |         |
            '----'         '---> HASH

.init() -> .update() -> .finup()
            ^    |         |
            '----'         '---> HASH

           .digest()
               |
               '---------------> HASH

Note that digest() is not an issue in the case we are discussing, since resource
allocation happens only in init().

Thanks,
Horia