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

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Date:	Thu, 10 Jul 2014 14:18:41 +0300
From:	Dmitry Kasatkin <d.kasatkin@...sung.com>
To:	Marek Vasut <marex@...x.de>,
	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	linux-ima-devel@...ts.sourceforge.net,
	linux-security-module <linux-security-module@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-crypto <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] ima: use ahash API for file hash calculation

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@...x.de> 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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