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Subject[PATCH v5] tpm: Add Upgrade/Reduced mode support for TPM2 modules
Date
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.

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

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)) {
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) {
+ dev_info(&chip->dev, "TPM is in failure mode, functionality limited\n");
+ 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
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