Re: [PATCH v5] tpm: Add Upgrade/Reduced mode support for TPM2 modules

[Jarkko Sakkinen <jarkko@kernel.org>]

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?

> 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).


> 
> 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.

>  		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?

> +		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).

> +		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