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

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Message-Id: <201407101002.07535.marex@denx.de>
Date:	Thu, 10 Jul 2014 10:02:07 +0200
From:	Marek Vasut <marex@...x.de>
To:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:	Dmitry Kasatkin <d.kasatkin@...sung.com>,
	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 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?

Best regards,
Marek Vasut
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