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

[Stefan Berger]

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