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

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Message-Id: <577545FE.5000206@linux.vnet.ibm.com>
Date:	Thu, 30 Jun 2016 12:17:02 -0400
From:	Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.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 06/27/2016 02:32 PM, Jarkko Sakkinen wrote:
> 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?

Not sure what to argue with. Maybe setting a bit on an ioctl that needs 
to be executed would be a good argument.

    stefan

>
> /Jarkko
>