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

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Message-Id: <9ff88c24-ca7a-1867-7284-17689fdac655@linux.vnet.ibm.com>
Date:   Thu, 25 May 2017 16:32:50 -0400
From:   Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     jarkko.sakkinen@...ux.intel.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 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