linux-kernel - Re: [PATCH] tpm: Add flag to use default cancellation policy

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Date:   Wed, 28 Sep 2022 05:10:25 +0000
From:   Joel Stanley <joel@....id.au>
To:     Eddie James <eajames@...ux.ibm.com>
Cc:     Jarkko Sakkinen <jarkko@...nel.org>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        peterhuewe@....de, jarkko@...nel.or, jgg@...pe.ca,
        Alexander.Steffen@...ineon.com
Subject: Re: [PATCH] tpm: Add flag to use default cancellation policy

On Thu, 8 Sept 2022 at 13:53, Eddie James <eajames@...ux.ibm.com> wrote:
>
>
> On 9/8/22 00:22, Jarkko Sakkinen wrote:
> > On Wed, Sep 07, 2022 at 11:43:17AM -0500, Eddie James wrote:
> >> The check for cancelled request depends on the VID of the chip, but
> >> some chips share VID which shouldn't share their cancellation
> >> behavior. This is the case for the Nuvoton NPCT75X, which should use
> >> the default cancellation check, not the Winbond one.
> >> To avoid changing the existing behavior, add a new flag to indicate
> >> that the chip should use the default cancellation check and set it
> >> for the I2C TPM2 TIS driver.
> >>
> >> Signed-off-by: Eddie James <eajames@...ux.ibm.com>
> >> ---
> >>   drivers/char/tpm/tpm_tis_core.c | 18 ++++++++++--------
> >>   drivers/char/tpm/tpm_tis_core.h |  1 +
> >>   drivers/char/tpm/tpm_tis_i2c.c  |  1 +
> >>   3 files changed, 12 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> >> index 757623bacfd5..175e75337395 100644
> >> --- a/drivers/char/tpm/tpm_tis_core.c
> >> +++ b/drivers/char/tpm/tpm_tis_core.c
> >> @@ -682,15 +682,17 @@ static bool tpm_tis_req_canceled(struct tpm_chip *chip, u8 status)
> >>   {
> >>      struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> >>
> >> -    switch (priv->manufacturer_id) {
> >> -    case TPM_VID_WINBOND:
> >> -            return ((status == TPM_STS_VALID) ||
> >> -                    (status == (TPM_STS_VALID | TPM_STS_COMMAND_READY)));
> >> -    case TPM_VID_STM:
> >> -            return (status == (TPM_STS_VALID | TPM_STS_COMMAND_READY));
> >> -    default:
> >> -            return (status == TPM_STS_COMMAND_READY);
> >> +    if (!test_bit(TPM_TIS_DEFAULT_CANCELLATION, &priv->flags)) {
> >> +            switch (priv->manufacturer_id) {
> >> +            case TPM_VID_WINBOND:
> >> +                    return ((status == TPM_STS_VALID) ||
> >> +                            (status == (TPM_STS_VALID | TPM_STS_COMMAND_READY)));
> >> +            case TPM_VID_STM:
> >> +                    return (status == (TPM_STS_VALID | TPM_STS_COMMAND_READY));
> >> +            }
> > Why there is no default: ?
>
>
> Well I didn't want to duplicate the line "status ==
> TPM_STS_COMMAND_READY" in the default case and for the flagged case. So
> now the switch just falls through for default. I can add default: break
> instead

This code was in the original patch series submitted by Nuvoton:

https://lore.kernel.org/r/20211104140211.6258-3-amirmizi6@gmail.com

Perhaps something like that would be better?

>
>
> >
> >>      }
> >> +
> >> +    return status == TPM_STS_COMMAND_READY;
> >>   }
> >>
> >>   static irqreturn_t tis_int_handler(int dummy, void *dev_id)
> >> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> >> index 66a5a13cd1df..b68479e0de10 100644
> >> --- a/drivers/char/tpm/tpm_tis_core.h
> >> +++ b/drivers/char/tpm/tpm_tis_core.h
> >> @@ -86,6 +86,7 @@ enum tis_defaults {
> >>   enum tpm_tis_flags {
> >>      TPM_TIS_ITPM_WORKAROUND         = BIT(0),
> >>      TPM_TIS_INVALID_STATUS          = BIT(1),
> >> +    TPM_TIS_DEFAULT_CANCELLATION    = BIT(2),
> >>   };
> >>
> >>   struct tpm_tis_data {
> >> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
> >> index 0692510dfcab..6722588e0217 100644
> >> --- a/drivers/char/tpm/tpm_tis_i2c.c
> >> +++ b/drivers/char/tpm/tpm_tis_i2c.c
> >> @@ -329,6 +329,7 @@ static int tpm_tis_i2c_probe(struct i2c_client *dev,
> >>      if (!phy->io_buf)
> >>              return -ENOMEM;
> >>
> >> +    set_bit(TPM_TIS_DEFAULT_CANCELLATION, &phy->priv.flags);
> > What if you just zeroed manufacturer ID?
>
>
> It's already zero there, and gets set to the VID as part of the core
> init function.
>
>
> Thanks,
>
> Eddie
>
>
> >
> >>      phy->i2c_client = dev;
> >>
> >>      /* must precede all communication with the tpm */
> >> --
> >> 2.31.1
> >>
> > BR, Jarkko