[PATCH v2 1/1] tpm: clear state post probing

[Simon Glass]

Hi Heinrich,

On Wed, 17 Nov 2021 at 12:28, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
>
>
> On 11/17/21 20:22, Ilias Apalodimas wrote:
> > Hi Simon,
> >
> >
> > On Wed, 17 Nov 2021 at 19:20, Simon Glass <sjg at chromium.org> wrote:
> >>
> >> Hi,
> >>
> >> (replying to both of you)
> >>
> >> On Wed, 17 Nov 2021 at 01:18, Ilias Apalodimas
> >> <ilias.apalodimas at linaro.org> wrote:
> >>>
> >>> Hi Simon,
> >>>
> >>>
> >>> On Wed, 17 Nov 2021 at 04:48, Simon Glass <sjg at chromium.org> wrote:
> >>>>
> >>>> Hi Heinrich,
> >>>>
> >>>> On Tue, 16 Nov 2021 at 04:08, Ilias Apalodimas
> >>>> <ilias.apalodimas at linaro.org> wrote:
> >>>>>
> >>>>> On Mon, Nov 15, 2021 at 08:30:06PM +0100, Heinrich Schuchardt wrote:
> >>>>>> Before we can start measuring the TPM must be cleared. Do this in the
> >>>>>> post_probe() method of the uclass.
> >>>>>>
> >>>>>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> >>>>>> ---
> >>>>>> v2:
> >>>>>>        tpm_startup2() is not available on all boards.
> >>>>>>        tpm_startup() takes care of translating the call.
> >>>>>> ---
> >>>>>>   drivers/tpm/tpm-uclass.c | 13 +++++++++++++
> >>>>>>   1 file changed, 13 insertions(+)
> >>>>>>
> >>>>>> diff --git a/drivers/tpm/tpm-uclass.c b/drivers/tpm/tpm-uclass.c
> >>>>>> index f67fe1019b..abd9ce35e8 100644
> >>>>>> --- a/drivers/tpm/tpm-uclass.c
> >>>>>> +++ b/drivers/tpm/tpm-uclass.c
> >>>>>> @@ -11,6 +11,7 @@
> >>>>>>   #include <log.h>
> >>>>>>   #include <linux/delay.h>
> >>>>>>   #include <linux/unaligned/be_byteshift.h>
> >>>>>> +#include <tpm_api.h>
> >>>>>>   #include <tpm-v1.h>
> >>>>>>   #include <tpm-v2.h>
> >>>>>>   #include "tpm_internal.h"
> >>>>>> @@ -136,6 +137,17 @@ int tpm_xfer(struct udevice *dev, const uint8_t *sendbuf, size_t send_size,
> >>>>>>        return 0;
> >>>>>>   }
> >>>>>>
> >>>>>> +static int dm_tpm_post_probe(struct udevice *dev)
> >>>>
> >>>> Please drop the dm_
> >>>>
> >>>>>> +{
> >>>>>> +     /*
> >>>>>> +      * Clearing the TPM state is only possible once after a hard reset.
> >>>>>> +      * As we do not know if the TPM has been cleared by a prior boot stage
> >>>>>> +      * ignore the return value here.
> >>>>>> +      */
> >>>>>> +     tpm_startup(dev, TPM_ST_CLEAR);
> >>>>
> >>>> blank line before final return
> >>>>
> >>>>>> +     return 0;
> >>>>>> +}
> >>>>
> >>>> This should only happen once and if the TPM is set up in SPL then this
> >>>> seems to cause a failure if done again.
> >>>>
> >>>
> >>> Not really. If you run the tpm_startup twice and the TPM is already
> >>> initialized you'll get TPM2_RC_INITIALIZE back. That's an 'error' you
> >>> can easily check against and decide.
> >>>
> >>>> Is there another way we can deal with this? Could the TPM user decide
> >>>> whether it needs to be set?
> >>>
> >>> Why? Part of the TPM init is making it usable.  We are trying to move
> >>> away from having to add something in the command line to make the
> >>> device usable.
> >>
> >> For a start, we should not start up the TPM until we need it. That
> >> goes against the U-Boot lazy-init approach. We already have a command
> >> to do it, as well as a TPM-API thing, so let's use that.
>
> The TPM is started exactly when we need it. When the user executes
> bootefi the TPM is probed if the TCG2 protocol is enabled because we
> need to measure binaries. Probing always has initialized TPMs. With this
> patch we only additionally clear it.
>
> This patch does not contradict lazy initialization.

I think it does, because you are calling a TPM operation in the
probe() method. Apart from the double-init problem you are creating, I
may not want to start the TPM at this point.

Regards,
Simon