linux-kernel - Re: [tpmdd-devel] [PATCH 09/13] tpm: Pull everything related to sysfs into tpm-sysfs.c

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Date:	Mon, 23 Sep 2013 16:23:24 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Daniel De Graaf <dgdegra@...ho.nsa.gov>
Cc:	tpmdd-devel@...ts.sourceforge.net,
	Leonidas Da Silva Barbosa <leosilva@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Rajiv Andrade <mail@...jiv.net>,
	Sirrix AG <tpmdd@...rix.com>
Subject: Re: [tpmdd-devel] [PATCH 09/13] tpm: Pull everything related to
 sysfs into tpm-sysfs.c

On Mon, Sep 23, 2013 at 06:00:46PM -0400, Daniel De Graaf wrote:

> In a PC client TPM, normal OS code (as opposed to firmware or microcode)
> is already restricted to locality 0-2. It may make sense to restrict
> locality 2 to the kernel, which would allow an in-kernel TPM seal
> command to be able to bind data so that userspace cannot unseal it.
> However, only allowing localities 0 and 1 to userspace may be too
> restrictive if userspace also wishes to use locality for separation,
> since locality 1 does not have the ability to reset any PCRs that
> locality 0 cannot also reset.
> The kernel could reserve only locality 1 for its own use, giving it the
> ability to seal data but not interfering with the ability to reset PCRs.
> This would be my preference, although it is less intuitive to allow code
> of lower privilege (userspace) to control the higher numbered locality
> 2.

This matches my vague understanding (we don't use localities here)

>> Perhaps a .config option would be useful to allow the system designer to
>> choose what, if any, locality to reserve for kernel use?

A runtime sysfs seems reasonable..

Would:
 user_default_locality
 kernel_default_locality
 user_allowed_localities (bitmask)
 supported_localities (bitmask)
 a GET_LOCALITY/SET_LOCALITY IOCTL to change localities of an open'd
  /dev/tpmX

Do the job?

At first glance anyhow. I wonder what in-kernel users would be
impacted by localities..

Any thoughts on root vs not-root? Would middelware want to use
localities?

Do you know anyone on the userspace SW side who could look at this?

Jason
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