Re: [tpmdd-devel] [PATCH v7 08/10] tpm: Proxy driver for supporting multiple emulated TPMs

Jarkko Sakkinen
2016-03-13T20:07:00Z

On Sat, Mar 12, 2016 at 06:27:13PM -0500, Stefan Berger wrote:
> Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote on 03/12/2016
> 01:51:54 PM:
>
> >
> > On Fri, Mar 11, 2016 at 09:51:03PM -0500, Stefan Berger wrote:
> > > This patch implements a proxy driver for supporting multiple emulated
> TPMs
> > > in a system.
> > >
> > > The driver implements a device /dev/vtpmx that is used to created
> > > a client device pair /dev/tpmX (e.g., /dev/tpm10) and a server side
> that
> > > is accessed using a file descriptor returned by an ioctl.
> > > The device /dev/tpmX is the usual TPM device created by the core TPM
> > > driver. Applications or kernel subsystems can send TPM commands to it
> > > and the corresponding server-side file descriptor receives these
> > > commands and delivers them to an emulated TPM.
> >
> > With my test script [1] running on QEMU and TPM 2.0 simulator running on
> the
> > host side I get this:
> >
> > $ python tpm2-simulator-vtpm --host=10.0.2.2
> > cmd
> > 80 01 00 00 00 0c 00 00 01 44 00 00
> > rsp
> > 80 01 00 00 00 0a 00 00 00 00
> > Traceback (most recent call last):
> > File "tpm2-simulator-vtpm", line 85, in <module>
> > main()
> > File "tpm2-simulator-vtpm", line 80, in main
> > resp = client.send_cmd(stream)
> > File "/home/tpmdd/tpm2-scripts/tpm2.py", line 454, in send_cmd
> > rsp = self.simulator.send_cmd(cmd)
> > File "/home/tpmdd/tpm2-scripts/tpm2.py", line 436, in send_cmd
> > raise SimulatorError("Empty response")
> > tpm2.SimulatorError: Empty response
> >
> > However, the process does not exit before the read call expires:
> >
> > $ python tpm2-list-handles
> > Traceback (most recent call last):
> > File "tpm2-list-handles", line 61, in <module>
> > main()
> > File "tpm2-list-handles", line 51, in main
> > handles += client.get_cap(tpm2.TPM2_CAP_HANDLES,
> tpm2.HR_LOADED_SESSION)
> > File "/home/tpmdd/tpm2-scripts/tpm2.py", line 782, in get_cap
> > next_handles, more_data = self.__get_cap_cnt(cap, pt, 1)
> > File "/home/tpmdd/tpm2-scripts/tpm2.py", line 766, in __get_cap_cnt
> > rsp = self.send_cmd(cmd)[10:]
> > File "/home/tpmdd/tpm2-scripts/tpm2.py", line 458, in send_cmd
> > rsp = f.read()
> > IOError: [Errno 62] Timer expired
> >
> > The server side stays stuck unti this happens.
>
> This fix should solve the problem:
>
> diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c
> b/drivers/char/tpm/tpm_vtpm_proxy.c
> index d73944e..01e5070 100644
> --- a/drivers/char/tpm/tpm_vtpm_proxy.c
> +++ b/drivers/char/tpm/tpm_vtpm_proxy.c
> @@ -456,10 +456,10 @@ err_delete_proxy_dev:
> */
> static void vtpm_proxy_delete_device(struct proxy_dev *proxy_dev)
> {
> - tpm_chip_unregister(proxy_dev->chip);
> -
> vtpm_proxy_fops_undo_open(proxy_dev);
>
> + tpm_chip_unregister(proxy_dev->chip);
> +
> vtpm_proxy_delete_proxy_dev(proxy_dev);
> }
>
> Can you let me know whether this gets it working for you? I'd prepare a
> v9.

So is the deadlock such that:

* tpm_chip_unregister() tries to write lock ops_sem.
* tpm_transmit() holds read lock to ops_sem.

This takes two minutes if no timeouts are calculated.

And is the effect of moving vtpm_proxy_fops_undo_open() upwards such
that vtpm_proxy_tpm_req_canceled() starts returning true, which in
effect breaks the loop in tpm_transmit()?

Yeah, the fix as a code change is very simple but I had to use perf
probe to verify this so maybe a comment there would be in place to
tell why tpm_chip_unregister() must be called last (write lock).

> Stefan

/Jarkko