Re: [PATCH v3 1/3] ima: use ahash API for file hash calculation

From: Dmitry Kasatkin
Date: Thu Jul 10 2014 - 07:20:12 EST

On 10/07/14 11:02, Marek Vasut wrote:
> On Thursday, July 10, 2014 at 01:05:39 AM, Dmitry Kasatkin wrote:
>> On 10 July 2014 00:00, Marek Vasut <marex@xxxxxxx> wrote:
>>> On Tuesday, July 08, 2014 at 10:07:16 AM, Dmitry Kasatkin wrote:
>>> [...]
>>>>> Right, but my concern is not about unloading the kernel module, but
>>>>> about the IMA module parameters left initialized. The existing code
>>>>> will continue using ahash (software version), even though the kernel
>>>>> module was unloaded, not shash. My question is about the software
>>>>> implementations of ahash vs. shash performance.
>>>>> Mimi
>>>> If HW driver will not be available, ahash loads generic driver which is
>>>> using shash.
>>>> Performance of that will be the same as for using shash directly.
>>> Hi Dmitry, I think Mimi is concerned about the crypto accelerator dying
>>> mid- flight.
>>> Imagine a situation where you have a hardware crypto accelerator
>>> connected via USB. You happily use IMA with this setup for days and then
>>> someone comes around and pulls the USB cable out. Will this be able to
>>> cope with such situation, for example by switching to software
>>> operations or such in some sane way ?
>>> I presume that's the concern here.
>>> Best regards,
>>> Marek Vasut
>> Hi Marek,
> Hi!
>> Nice to here from you. How was your rest stay at Japan?
> Thanks for asking, not sure there is a super-positive ultra-awesome word to
> express that, so in short, I had the time of my life. Love that country ;-)
>> I have not seen any expression of such concern.
> All right, that was my understanding of the entire discussion -- an accelerator
> dying mid-way and what will IMA do about that.
>> But as we fallback to early allocated shash, which is not USB yet,
>> then there is no problem.
>> ahash itself does not bring any other additional problem than shash itself.
>> They are compiled builtin together.
> Sure, I understood that. But what will happen if the ahash accelerator stops
> working mid-flight, will IMA also go bonkers or is there some graceful stop?

shash fallback will be used.

> Best regards,
> Marek Vasut

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