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

[Jerry Snitselaar <jsnitsel@xxxxxxxxxx>]

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,
};

-static const struct attribute_group tpm_dev_group = {
-       .attrs = tpm_dev_attrs,
+static struct attribute *tpm20_dev_attrs[] = {
+       &dev_attr_version_major.attr,
+       NULL
+};
+
+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.