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

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Message-Id: <f6c024ae-fe93-251a-a176-1f27f25b1e21@linux.vnet.ibm.com>
Date:   Thu, 25 May 2017 16:04:24 -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 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.

     Stefan