linux-kernel - Re: [tpmdd-devel] [PATCH] TPM: Fixup pubek sysfs file

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Date:	Mon, 14 Sep 2009 12:50:00 -0700
From:	Greg KH <greg@...ah.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	"Jonathan M. McCune" <jonmccune@....edu>,
	Rajiv Andrade <srajiv@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, jbeulich@...ell.com,
	jmorris@...ei.org, tpmdd-devel@...ts.sourceforge.net,
	m.selhorst@...rix.com, Andrew Morton <akpm@...ux-foundation.org>,
	Roland Dreier <rdreier@...co.com>,
	Reiner Sailer <sailer@...ibm.com>
Subject: Re: [tpmdd-devel] [PATCH] TPM: Fixup pubek sysfs file

On Mon, Sep 14, 2009 at 01:46:26PM -0600, Jason Gunthorpe wrote:
> On Mon, Sep 14, 2009 at 03:23:09PM -0400, Jonathan M. McCune wrote:
> 
> >> Can anyone think of a reason why the PCRs should be accessed from
> >> sysfs? I can't. They are only really useful in connection with other
> >> complex TPM operations. Userspace can fully access them using the
> >> relevant TPM calls.
> >
> > Fair enough, though they are useful in combination with IMA and as a  
> > sanity check that the driver is working correctly.
> [..]
> > IMA can leverage the ability to read and extend PCRs, and its security  
> > properties derive from that functionality being a part of the kernel.  
> > PCR reading is currently part of the TPM driver in 
> > drivers/char/tpm/tpm.c.
> 
> Sanzzy
> 
> > Thus, to the question, "Can we remove the ability of the kernel to send  
> > TPM commands such as GetCapability and PCRRead?" I believe the answer is  
> > no. Or at least, not without causing a lot of work for the IMA system.  
> > Although it may be worth discussing whether this functionality should be  
> > moved from the driver into IMA.
> 
> Fair enough, fortunately TPM_PCRRead and TPM_Extend are two of the
> simplest commands. As has been done special casing the fixed size
> messages is easy and robust.
> 
> The pcrs file really isn't that offsensive to me, the PCR registers
> can reasonably thought of as a single memory space. If it wasn't for
> the PCR-%u prefix I think it would be fine for sysfs??
> 
> Ie:
> 
> BD ED 7B B2 EB AE BE 31 4E CC 57 82 81 64 FC 8A 09 FA 19 25 
> 05 37 25 B5 24 59 14 A5 94 1A 42 97 39 E6 07 40 27 3A 7D 48 
> 3A 3F 78 0F 11 A4 B4 99 69 FC AA 80 CD 6E 39 57 C3 3B 22 75 
> 
> not:
> 
> PCR-00: BD ED 7B B2 EB AE BE 31 4E CC 57 82 81 64 FC 8A 09 FA 19 25 
> PCR-01: 05 37 25 B5 24 59 14 A5 94 1A 42 97 39 E6 07 40 27 3A 7D 48 
> PCR-02: 3A 3F 78 0F 11 A4 B4 99 69 FC AA 80 CD 6E 39 57 C3 3B 22 75 
> 
> Greg?

That should just be a binary sysfs file, as it shows something that is
represented in hardware, not anything that is modified by the kernel,
right?

thanks,

greg k-h
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