linux-kernel - Re: [PATCH] tpm: vtpm_proxy: Do not run tpm2

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Message-ID: <20170525223348.uh66n37dnvz3eptl@intel.com>
Date:   Thu, 25 May 2017 15:33:48 -0700
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-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: vtpm_proxy: Do not run tpm2_shutdown

On Thu, May 25, 2017 at 04:32:50PM -0400, Stefan Berger wrote:
> On 05/25/2017 04:09 PM, Jason Gunthorpe wrote:
> > On Thu, May 25, 2017 at 04:04:24PM -0400, Stefan Berger wrote:
> > > On 05/25/2017 11:50 AM, Jason Gunthorpe wrote:
> > > > On Thu, May 25, 2017 at 09:12:36AM -0400, Stefan Berger wrote:
> > > > > The tpm2_shutdown does not work with the VTPM proxy driver since the
> > > > > function only gets called when the backend file descriptor is already
> > > > > closed and at this point no data can be sent anymore. A proper shutdown
> > > > > would have to be initated by a user space application, such as a container
> > > > > management stack, that sends the command via the character device before
> > > > > terminating the TPM emulator.
> > > > > 
> > > > > To avoid the tpm2_shutdown we introduce a TPM_CHIP_FLAG_NO_SHUTDOWN flag
> > > > > that only the VTPM proxy driver sets. This also avoids misleading kernel
> > > > > log messages.
> > > > This seems strange to me..
> > > > 
> > > > Why isn't ops null if the fd has gone away?
> > > > 
> > > > What is the call flow that hits this?
> > > In this function here.
> > > 
> > > static void tpm_del_char_device(struct tpm_chip *chip)
> > > {
> > >      cdev_device_del(&chip->cdev, &chip->dev);
> > > 
> > >      /* Make the chip unavailable. */
> > >      mutex_lock(&idr_lock);
> > >      idr_replace(&dev_nums_idr, NULL, chip->dev_num);
> > >      mutex_unlock(&idr_lock);
> > > 
> > >      /* Make the driver uncallable. */
> > >      down_write(&chip->ops_sem);
> > >      if (chip->flags & TPM_CHIP_FLAG_TPM2)
> > >          tpm2_shutdown(chip, TPM2_SU_CLEAR);
> > >      chip->ops = NULL;
> > >      up_write(&chip->ops_sem);
> > > }
> > > 
> > > The request cannot be deliver because the anonymous fd has been closed
> > > already.
> > The driver must always be able to process requests until
> > tpm_del_char_device completes, so this is triggering an existing bug
> > in vtpm. This change in core behvior is not going to fix the bug.
> > 
> > eg a request from sysfs/etc could come in between vtpm fd closure and
> > tpm_del_char_device, and it still must be handled properly.
> > 
> > I guess you need to have transmit command fail fast once the fd is
> > closed.
> 
> It doesn't hang. Everything is torn down immediately. What is primarily
> annoying are these two log messages:
> tpm tpm0: tpm_transmit: tpm_send: error -32
> tpm tpm0: transmit returned -32 while stopping the TPM
> 
> 
>     Stefan

It's been a while since I've looked into vtpm code. Why was fd closed
before the above? I can go this through myself once I'm back in Finland
next week. Just have forgotten this detail and do not have time to study
this right now.

/Jarkko