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

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Message-ID: <14364c45-8f56-e6d6-66f2-8357bf89a894@denx.de>
Date:   Thu, 15 Feb 2018 19:32:31 +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 07:06 PM, Kamil Konieczny wrote:
> 
> 
> On 15.02.2018 18:06, Marek Vasut wrote:
>> 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 ...
>>
> 
> Why you want checks for something that not exist ?
> 
> Those without them will not work and will do Oops in crypto testmgr,
> so such drivers should not be used nor accepted in drivers/crypto
> 
> Ask yourself why crypto do not check for NULL in ahash digest or other
> required ahash functions.

Are you suggesting that the kernel code should NOT perform NULL pointer
checks ?

Are you suggesting each driver should implement every single callback
available and if it is not implemented, return -ENOSYS ? This looks like
a MASSIVE code duplication.

>>> 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.
> 
> Now size of crypto core is reduced.

You implemented the same code thrice, it surely is not reduced.

-- 
Best regards,
Marek Vasut