[LTP] [PATCH] ima: skip verifying TPM 2.0 PCR values

[Jerry Snitselaar]

On Thu Oct 24 19, Mimi Zohar wrote:
>On Thu, 2019-10-24 at 14:38 -0700, Jerry Snitselaar wrote:
>> On Thu Oct 24 19, Jarkko Sakkinen wrote:
>> >On Thu, Oct 24, 2019 at 02:18:48PM +0200, Petr Vorel wrote:
>> >> Hi all,
>> >>
>> >> I wonder what to do with this patch "ima: skip verifying TPM 2.0 PCR values" [1].
>> >> Is it a correct way to differentiate between TPM 1.2 and TPM 2.0?
>> >> Or something else should be applied?
>> >>
>> >> How is the work on TPM 2.0 Linux sysfs interface?
>> >> But even it's done in near future, we'd still need some way for older kernels.
>> >>
>> >> Kind regards,
>> >> Petr
>> >>
>> >> [1] https://patchwork.ozlabs.org/patch/1100733/
>> >
>> >version_major sysfs file would be acceptable if someone wants to proceed
>> >and send such patch.
>> >
>> >Also replicants for durations and timeouts files would make sense for
>> >TPM 2.0.
>> >
>> >/Jarkko
>>
>> Is it as simple as doing this?
>>
>> diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c
>> index edfa89160010..fd8eb8d8945c 100644
>> --- a/drivers/char/tpm/tpm-sysfs.c
>> +++ b/drivers/char/tpm/tpm-sysfs.c
>> @@ -309,7 +309,17 @@ static ssize_t timeouts_show(struct device *dev, struct device_attribute *attr,
>>  }
>>  static DEVICE_ATTR_RO(timeouts);
>>
>> -static struct attribute *tpm_dev_attrs[] = {
>> +static ssize_t version_major_show(struct device *dev,
>> +                                 struct device_attribute *attr, char *buf)
>> +{
>> +       struct tpm_chip *chip = to_tpm_chip(dev);
>> +
>> +       return sprintf(buf, "TPM%s\n", chip->flags & TPM_CHIP_FLAG_TPM2
>> +                      ? "2.0" : "1.2");
>> +}
>> +static DEVICE_ATTR_RO(version_major);
>> +
>> +static struct attribute *tpm12_dev_attrs[] = {
>>         &dev_attr_pubek.attr,
>>         &dev_attr_pcrs.attr,
>>         &dev_attr_enabled.attr,
>> @@ -320,18 +330,28 @@ static struct attribute *tpm_dev_attrs[] = {
>>         &dev_attr_cancel.attr,
>>         &dev_attr_durations.attr,
>>         &dev_attr_timeouts.attr,
>> +       &dev_attr_version_major.attr,
>>         NULL,
>>  };
>>
>
>The TPM version seems to be included in "dev_attr_caps.attr".
>
>> -static const struct attribute_group tpm_dev_group = {
>> -       .attrs = tpm_dev_attrs,
>> +static struct attribute *tpm20_dev_attrs[] = {
>> +       &dev_attr_version_major.attr,
>> +       NULL
>> +};
>
>This should work, but wouldn't exporting this information under
>security/tpmX, like the binary_bios_measurements, be a lot easier to
>find and use?
>
>Mimi
>

/sys/kernel/security/tpmX/major_version (on fedora and rhel at least, is it elsewhere on other distros?)

versus

/sys/class/tpm/tpmX/major_version

I don't know that it is any easier to find.

>> +
>> +static const struct attribute_group tpm12_dev_group = {
>> +       .attrs = tpm12_dev_attrs,
>> +};
>> +
>> +static const struct attribute_group tpm20_dev_group = {
>> +       .attrs = tpm20_dev_attrs,
>>  };
>>
>>  void tpm_sysfs_add_device(struct tpm_chip *chip)
>>  {
>> -       if (chip->flags & TPM_CHIP_FLAG_TPM2)
>> -               return;
>> -
>>         WARN_ON(chip->groups_cnt != 0);
>> -       chip->groups[chip->groups_cnt++] = &tpm_dev_group;
>> +       if (chip->flags & TPM_CHIP_FLAG_TPM2)
>> +               chip->groups[chip->groups_cnt++] = &tpm20_dev_group;
>> +       else
>> +               chip->groups[chip->groups_cnt++] = &tpm12_dev_group;
>>  }
>>
>>
>> Did a quick test on 2 systems here.
>