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SubjectRe: [PATCH v5] tpm: Add Upgrade/Reduced mode support for TPM2 modules
On Tue, Aug 10, 2021 at 07:53:12PM +0200, Jarkko Sakkinen wrote:
> On Mon, Aug 09, 2021 at 07:47:30PM +0200, Borys Movchan wrote:
> > If something went wrong during the TPM firmware upgrade, like power
> > failure or the firmware image file get corrupted, the TPM might end
> > up in Upgrade or Failure mode upon the next start. The state is
> > persistent between the TPM power cycle/restart.
> >
> > According to TPM specification:
> > * If the TPM is in Upgrade mode, it will answer with TPM2_RC_UPGRADE
> > to all commands except Field Upgrade related ones.
> > * If the TPM is in Failure mode, it will allow performing TPM
> > initialization but will not provide any crypto operations.
> > Will happily respond to Field Upgrade calls.
> >
> > Change the behavior of the tpm2_auto_startup(), so it detects the active
> > running mode of the TPM by adding the following checks. If
> > tpm2_do_selftest() call returns TPM2_RC_UPGRADE, the TPM is in Upgrade
> > mode.
> > If the TPM is in Failure mode, it will successfully respond to both
> > tpm2_do_selftest() and tpm2_startup() calls. Although, will fail to
> > answer to tpm2_get_cc_attrs_tbl(). Use this fact to conclude that TPM is
> > in Failure mode.
> >
> > If detected that the TPM is in the Upgrade or Failure mode, the function
> > sets TPM_CHIP_FLAG_LIMITED_MODE flag.
>
> Does this apply for TPM 1.2? Are there differences?
>

Actually I am not sure, I am working with TPM 2 exclusively have no
knowledge regarding other versions.

> > The limited mode flag is used later during driver
> > initialization/deinitialization to disable functionality which makes no
> > sense or will fail in the current TPM state. Following functionality is
> > affected:
> > * do not register TPM as a hwrng
> > * do not register sysfs entries which provide information impossible to
> > obtain in limited mode
> > * do not register resource managed character device
>
> Maybe for consistency call it TPM_CHIP_FLAG_UPGRADE_MODE? It makes easier
> to "connect dots" later on (has probably something to do TPM_RC_UPGRADE).
>
>

My idea was to group both Failure and Upgrade mode and call them limited
mode. As functionality of the TPM is limited in both of them. I was
afraid that if I call it upgrade mode and map failure mode into it, it
might get confusing. So please confirm that you prefer to name the flag
as TPM_CHIP_FLAG_UPGRADE_MODE.

> >
> > Signed-off-by: Borys Movchan <borysmn@axis.com>
> > ---
> >
> > Notes:
> > v2:
> > * Commit message updated.
> >
> > v3:
> > * Commit message reworked.
> >
> > v4:
> > * Description of how tpm2_auto_startup() detects the mode added to
> > commit message.
> >
> > v5:
> > * Introduce global flag: TPM_CHIP_FLAG_LIMITED_MODE.
> > * Add checks for the flag in places that will not work properly when TPM
> > functionality is limited.
> > * Avoid registering sysfs and character device entries that have no useful
> > function in limited mode.
> > * Do not register TPM as a hwrng.
> > * Do not try to obtain any crypto-related properties from TPM as it will fail
> > in limited mode.
> >
> > drivers/char/tpm/tpm-chip.c | 16 ++++++++++------
> > drivers/char/tpm/tpm-sysfs.c | 3 +++
> > drivers/char/tpm/tpm2-cmd.c | 13 ++++++++++++-
> > include/linux/tpm.h | 2 ++
> > 4 files changed, 27 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> > index ddaeceb7e109..8d159db39392 100644
> > --- a/drivers/char/tpm/tpm-chip.c
> > +++ b/drivers/char/tpm/tpm-chip.c
> > @@ -444,7 +444,7 @@ static int tpm_add_char_device(struct tpm_chip *chip)
> > return rc;
> > }
> >
> > - if (chip->flags & TPM_CHIP_FLAG_TPM2) {
> > + if (chip->flags & TPM_CHIP_FLAG_TPM2 && !(chip->flags & TPM_CHIP_FLAG_LIMITED_MODE)) {
>
> You cannot rely on validity of TPM_CHIP_FLAG_TPM2, as tpm_tis driver
> uses a TPM command to probe the TPM version.
>

Good point, will fix in next patch version.

> > rc = cdev_device_add(&chip->cdevs, &chip->devs);
> > if (rc) {
> > dev_err(&chip->devs,
> > @@ -506,7 +506,8 @@ static int tpm_add_legacy_sysfs(struct tpm_chip *chip)
> > struct attribute **i;
> > int rc;
> >
> > - if (chip->flags & (TPM_CHIP_FLAG_TPM2 | TPM_CHIP_FLAG_VIRTUAL))
> > + if (chip->flags & (TPM_CHIP_FLAG_TPM2 | TPM_CHIP_FLAG_VIRTUAL) ||
> > + chip->flags & TPM_CHIP_FLAG_LIMITED_MODE)
> > return 0;
> >
> > rc = compat_only_sysfs_link_entry_to_kobj(
> > @@ -536,7 +537,7 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> >
> > static int tpm_add_hwrng(struct tpm_chip *chip)
> > {
> > - if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
> > + if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM) || chip->flags & TPM_CHIP_FLAG_LIMITED_MODE)
> > return 0;
> >
> > snprintf(chip->hwrng_name, sizeof(chip->hwrng_name),
> > @@ -550,6 +551,9 @@ static int tpm_get_pcr_allocation(struct tpm_chip *chip)
> > {
> > int rc;
> >
> > + if (chip->flags & TPM_CHIP_FLAG_LIMITED_MODE)
> > + return 0;
> > +
> > rc = (chip->flags & TPM_CHIP_FLAG_TPM2) ?
> > tpm2_get_pcr_allocation(chip) :
> > tpm1_get_pcr_allocation(chip);
> > @@ -612,7 +616,7 @@ int tpm_chip_register(struct tpm_chip *chip)
> > return 0;
> >
> > out_hwrng:
> > - if (IS_ENABLED(CONFIG_HW_RANDOM_TPM))
> > + if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !(chip->flags & TPM_CHIP_FLAG_LIMITED_MODE))
> > hwrng_unregister(&chip->hwrng);
> > out_ppi:
> > tpm_bios_log_teardown(chip);
> > @@ -637,10 +641,10 @@ EXPORT_SYMBOL_GPL(tpm_chip_register);
> > void tpm_chip_unregister(struct tpm_chip *chip)
> > {
> > tpm_del_legacy_sysfs(chip);
> > - if (IS_ENABLED(CONFIG_HW_RANDOM_TPM))
> > + if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !(chip->flags & TPM_CHIP_FLAG_LIMITED_MODE))
> > hwrng_unregister(&chip->hwrng);
> > tpm_bios_log_teardown(chip);
> > - if (chip->flags & TPM_CHIP_FLAG_TPM2)
> > + if (chip->flags & TPM_CHIP_FLAG_TPM2 && !(chip->flags & TPM_CHIP_FLAG_LIMITED_MODE))
> > cdev_device_del(&chip->cdevs, &chip->devs);
> > tpm_del_char_device(chip);
> > }
> > diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c
> > index 63f03cfb8e6a..43ea9c66342d 100644
> > --- a/drivers/char/tpm/tpm-sysfs.c
> > +++ b/drivers/char/tpm/tpm-sysfs.c
> > @@ -478,6 +478,9 @@ void tpm_sysfs_add_device(struct tpm_chip *chip)
> > {
> > int i;
> >
> > + if (chip->flags & TPM_CHIP_FLAG_LIMITED_MODE)
> > + return;
> > +
> > WARN_ON(chip->groups_cnt != 0);
> >
> > if (chip->flags & TPM_CHIP_FLAG_TPM2)
> > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > index a25815a6f625..598d62695310 100644
> > --- a/drivers/char/tpm/tpm2-cmd.c
> > +++ b/drivers/char/tpm/tpm2-cmd.c
> > @@ -729,7 +729,12 @@ int tpm2_auto_startup(struct tpm_chip *chip)
> > goto out;
> >
> > rc = tpm2_do_selftest(chip);
> > - if (rc && rc != TPM2_RC_INITIALIZE)
> > + if (rc == TPM2_RC_UPGRADE) {
> > + dev_info(&chip->dev, "TPM is in upgrade mode, functionality limited\n");
> > + chip->flags |= TPM_CHIP_FLAG_LIMITED_MODE;
> > + rc = 0;
> > + goto out;
> > + } else if (rc && rc != TPM2_RC_INITIALIZE)
> > goto out;
> >
> > if (rc == TPM2_RC_INITIALIZE) {
> > @@ -743,6 +748,12 @@ int tpm2_auto_startup(struct tpm_chip *chip)
> > }
> >
> > rc = tpm2_get_cc_attrs_tbl(chip);
> > + if (rc) {
>
> Why all rc's apply?
>

Different vendors return different error codes here. Some, like STM
return vendor specific ones.

> > + dev_info(&chip->dev, "TPM is in failure mode, functionality limited\n");
>
> Here is again a different name for the same thing (different than
> TPM_CHIP_FLAG_LIMITED_MODE).
>

This check is triggered only if TPM is in Failure mode. It is different
from Upgrade mode.

> > + chip->flags |= TPM_CHIP_FLAG_LIMITED_MODE;
> > + rc = 0;
> > + goto out;
> > + }
> >
> > out:
> > if (rc > 0)
> > diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> > index aa11fe323c56..231d7c7ec913 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -207,6 +207,7 @@ enum tpm2_return_codes {
> > TPM2_RC_INITIALIZE = 0x0100, /* RC_VER1 */
> > TPM2_RC_FAILURE = 0x0101,
> > TPM2_RC_DISABLED = 0x0120,
> > + TPM2_RC_UPGRADE = 0x012D,
> > TPM2_RC_COMMAND_CODE = 0x0143,
> > TPM2_RC_TESTING = 0x090A, /* RC_WARN */
> > TPM2_RC_REFERENCE_H0 = 0x0910,
> > @@ -277,6 +278,7 @@ enum tpm_chip_flags {
> > TPM_CHIP_FLAG_HAVE_TIMEOUTS = BIT(4),
> > TPM_CHIP_FLAG_ALWAYS_POWERED = BIT(5),
> > TPM_CHIP_FLAG_FIRMWARE_POWER_MANAGED = BIT(6),
> > + TPM_CHIP_FLAG_LIMITED_MODE = BIT(7),
> > };
> >
> > #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)
> > --
> > 2.20.1
> >
> >
>
> /Jarkko

Kind regards,
Borys

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