linux-kernel - Re: [PATCH v3 0/5] crypto: ahash.c: Require export/import in ahash

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Date:   Thu, 15 Feb 2018 18:06:17 +0100
From:   Marek Vasut <marex@...x.de>
To:     Kamil Konieczny <k.konieczny@...tner.samsung.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux-crypto@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sonic Zhang <sonic.zhang@...log.com>,
        Fabio Estevam <fabio.estevam@...escale.com>,
        Shawn Guo <shawn.guo@...aro.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Jan Engelhardt <jengelh@...i.de>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Joakim Bech <joakim.bech@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/5] crypto: ahash.c: Require export/import in ahash

On 02/15/2018 06:00 PM, Kamil Konieczny wrote:
> 
> 
> On 15.02.2018 17:27, Marek Vasut wrote:
>> On 02/15/2018 04:41 PM, Herbert Xu wrote:
>>> On Thu, Jan 18, 2018 at 07:33:59PM +0100, Kamil Konieczny wrote:
>>>> First four patches add empty hash export and import functions to each driver,
>>>> with the same behaviour as in crypto framework. The last one drops them from
>>>> crypto framework. Last one for ahash.c depends on all previous.
>>>>
>>>> Changes in v3:
>>>> added change for bfin_crc.c
>>>> make this a patchset, instead of unreleated patches
>>>> make commit message more descriptive
>>>>
>>>> Kamil Konieczny (5):
>>>>   crypto: mxs-dcp: Add empty hash export and import
>>>>   crypto: n2_core: Add empty hash export and import
>>>>   crypto: ux500/hash: Add empty export and import
>>>>   crypto: bfin_crc: Add empty hash export and import
>>>>   crypto: ahash.c: Require export/import in ahash
>>>>
>>>>  crypto/ahash.c                        | 18 ++----------------
>>>>  drivers/crypto/bfin_crc.c             | 12 ++++++++++++
>>>>  drivers/crypto/mxs-dcp.c              | 14 ++++++++++++++
>>>>  drivers/crypto/n2_core.c              | 12 ++++++++++++
>>>>  drivers/crypto/ux500/hash/hash_core.c | 18 ++++++++++++++++++
>>>>  5 files changed, 58 insertions(+), 16 deletions(-)
>>>
>>> All applied.  Thanks.
>>
>> This makes no sense, cfr my comment on 5/5
>>
>> Seems like if the driver doesn't implement those, the core can easily
>> detect that and perform the necessary action. Moving the checks out of
>> core seems like the wrong thing to do, rather you should enhance the
>> checks in core if they're insufficient in my opinion.
> 
> The bug can only be in driver which will not implement those two functions,
> but we already had all drivers with those due to patches 1..4
> All other drivers do have them.

The core can very well check if these functions are not populated and
return ENOSYS

> Additionally, with crypto we want minimize code and run as fast as possible.

So you remove all NULL pointer checks ? Esp. in security-sensitive code?
What is the impact of this non-critical path code on performance?

Come on ...

> Moving checks out of core will impose on driver author need for implement
> those functions, or declare them empty, but in case of empty ones 
> crypto will not work properly with such driver.

You can very well impose that in the core, except you don't duplicate
the code.

-- 
Best regards,
Marek Vasut