| Message ID | 20240913200517.3085794-19-ross.philipson@oracle.com |
|---|---|
| State | New |
| Headers | show |
| Series | x86: Trenchboot secure dynamic launch Linux kernel support | expand |
On Fri, 2024-09-13 at 13:05 -0700, Ross Philipson wrote: > Expose a sysfs interface to allow user mode to set and query the > default locality set for the TPM chip. What does a user need this for? It somewhat conflicts with the idea of running the kernel and user space TPM access in separate localities for the purposes of key release, so we can seal keys to only release in the kernel by policy. When I last talked about this I thought we'd probably use 0 for user and, say 2, for the kernel (mainly because prior incarnations of this patch set seemed to access the TPM in locality 2 from the kernel). It really doesn't matter *what* locality we use for the kernel and the user as long as it's known ahead of time and the user can't gain access to the kernel locality. Regards, James
On Fri Sep 13, 2024 at 11:05 PM EEST, Ross Philipson wrote: > Expose a sysfs interface to allow user mode to set and query the default > locality set for the TPM chip. > > Signed-off-by: Ross Philipson <ross.philipson@oracle.com> Must be read-only. Should be decided per power cycle. BR, Jarkko
On Fri Nov 1, 2024 at 12:06 PM EET, Jarkko Sakkinen wrote: > On Fri Sep 13, 2024 at 11:05 PM EEST, Ross Philipson wrote: > > Expose a sysfs interface to allow user mode to set and query the default > > locality set for the TPM chip. > > > > Signed-off-by: Ross Philipson <ross.philipson@oracle.com> > > Must be read-only. Should be decided per power cycle. I'm throwing one incomplete idea not all things considered... So one idea is would be to apply set operation to /dev/tpm0 as ioctl (would not be available for /dev/tpmrm0). Then at least access control rules would apply. The open here is that the IMA etc. will use a different locality during boot-time, like it would also with sysfs attribute. BR, Jarkko
On Fri Nov 1, 2024 at 11:50 PM EET, Jarkko Sakkinen wrote: > On Fri Nov 1, 2024 at 12:06 PM EET, Jarkko Sakkinen wrote: > > On Fri Sep 13, 2024 at 11:05 PM EEST, Ross Philipson wrote: > > > Expose a sysfs interface to allow user mode to set and query the default > > > locality set for the TPM chip. > > > > > > Signed-off-by: Ross Philipson <ross.philipson@oracle.com> > > > > Must be read-only. Should be decided per power cycle. > > I'm throwing one incomplete idea not all things considered... > > So one idea is would be to apply set operation to /dev/tpm0 as ioctl > (would not be available for /dev/tpmrm0). > > Then at least access control rules would apply. > > The open here is that the IMA etc. will use a different locality during > boot-time, like it would also with sysfs attribute. Looking at [1] this would become a problem if TPM2_PolicyLocality based policy is ever used during boot-time. We can make a choice of not allowing such policies for in-kernel clients if agree so, but it is a choice that needs to be locked in. With quick thinking I'm not sure if that is horrible limitation. Also does not obviously affect clients communicating with /dev/tpm0. With that constrain it would not matter if during boot-time different locale is used. With that constraint and "set" in ioctl instead of sysfs attributes that might even work out... Open for feedback. [1] https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-3-Commands.pdf BR, Jarkko
diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c index 94231f052ea7..185a2f57d4cb 100644 --- a/drivers/char/tpm/tpm-sysfs.c +++ b/drivers/char/tpm/tpm-sysfs.c @@ -324,6 +324,34 @@ static ssize_t null_name_show(struct device *dev, struct device_attribute *attr, static DEVICE_ATTR_RO(null_name); #endif +static ssize_t default_locality_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + struct tpm_chip *chip = to_tpm_chip(dev); + + return sprintf(buf, "%d\n", chip->default_locality); +} + +static ssize_t default_locality_store(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count) +{ + struct tpm_chip *chip = to_tpm_chip(dev); + unsigned int locality; + + if (kstrtouint(buf, 0, &locality)) + return -ERANGE; + + if (locality >= TPM_MAX_LOCALITY) + return -ERANGE; + + if (tpm_chip_set_default_locality(chip, (int)locality)) + return count; + else + return 0; +} + +static DEVICE_ATTR_RW(default_locality); + static struct attribute *tpm1_dev_attrs[] = { &dev_attr_pubek.attr, &dev_attr_pcrs.attr, @@ -336,6 +364,7 @@ static struct attribute *tpm1_dev_attrs[] = { &dev_attr_durations.attr, &dev_attr_timeouts.attr, &dev_attr_tpm_version_major.attr, + &dev_attr_default_locality.attr, NULL, }; @@ -344,6 +373,7 @@ static struct attribute *tpm2_dev_attrs[] = { #ifdef CONFIG_TCG_TPM2_HMAC &dev_attr_null_name.attr, #endif + &dev_attr_default_locality.attr, NULL };
Expose a sysfs interface to allow user mode to set and query the default locality set for the TPM chip. Signed-off-by: Ross Philipson <ross.philipson@oracle.com> --- drivers/char/tpm/tpm-sysfs.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)