linux-kernel - Re: [PATCH] tpm: vtpm_proxy: Introduce flag to prevent sysfs entries

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Date:	Mon, 27 Jun 2016 21:32:20 +0300
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] tpm: vtpm_proxy: Introduce flag to prevent sysfs entries

On Fri, Jun 24, 2016 at 02:43:00PM -0400, Stefan Berger wrote:
> On 06/24/2016 01:48 PM, Jason Gunthorpe wrote:
> >On Fri, Jun 24, 2016 at 10:36:55AM -0400, Stefan Berger wrote:
> >>Introduce TPM_VTPM_PROXY_NO_SYSFS flag that prevents a vtpm_proxy driver
> >>instance from having the typical sysfs entries that shows the state of the
> >>TPM. The flag is to be set in the ioctl creating the vtpm_proxy device
> >>pair and maps on a new chip flags TPM_CHIP_FLAG_NO_SYSFS.
> >No other subsystem does something so goofy, this really needs to be
> >part of namespace support for TPM.
> 
> And I am not sure how to go about this. TPM2 by the way doesn't have such
> entries, so it's much better from that perspective.
> 
> >
> >Why can't you just make the sysfs files unreadable in user space?
> 
> There are actually ways to go about this. Likely bind-mounting over
> /sys/device/virtual/tpm would be one solution to hide all virtual TPM
> device. Another is applying an AppArmor policy to the container denying
> access to tpm directories or entries. SELinux would not be so easy.
> 
> The flag in this patch seemed like a 'cheap' way to eliminate that problem
> as well.

Does it have any other qualities that would make this better than bind
mounting?

/Jarkko