Re: [PATCH v6] tpm: Add Upgrade/Reduced mode support for TPM2 modules

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, 2021-09-30 at 18:02 +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.

How many such command are there and what they are? This patch is missing
the part that filters in only these commands.

>  * 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_FIRMWARE_UPGRADE_MODE flag.

I think we should shorten this to TPM_CHIP_FLAG_FIRMWARE_MODE. It's clear
enough and just easier for eyes, really.

> The limited mode flag is used later during driver

You probably have forgot to update commit message over here? Please try to
align it with the code changes.

> 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

Nit: "do" -> "Do"

>  * do not register sysfs entries which provide information impossible to
>    obtain in limited mode
>  * do not register resource managed character device

Ditto.

> 
> 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.
>     
>     v6:
>      * Rename the TPM_CHIP_FLAG_LIMITED_MODE to TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE
>        to reduce confusion. Update info messages.
> 
>  drivers/char/tpm/tpm-chip.c  | 23 ++++++++++++++++-------
>  drivers/char/tpm/tpm-sysfs.c |  3 +++
>  drivers/char/tpm/tpm2-cmd.c  | 14 +++++++++++++-
>  include/linux/tpm.h          |  2 ++
>  4 files changed, 34 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index ddaeceb7e109..3378bfe06006 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -444,7 +444,8 @@ 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_FIRMWARE_UPGRADE_MODE)) {

Please do this instead in tpm.h, give that the check is everywhere:

/*
 * Check if TPM device is in the firmware upgrade mode.
 */
static inline bool tpm_is_firmware_upgrade(void)
{
	return chip->flags & TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE;
}


Makes the code less stressing to read (and find the decision points
later on with tools).

>  		rc = cdev_device_add(&chip->cdevs, &chip->devs);
>  		if (rc) {
>  			dev_err(&chip->devs,
> @@ -488,7 +489,8 @@ static void tpm_del_legacy_sysfs(struct tpm_chip *chip)
>  {
>  	struct attribute **i;
>  
> -	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_FIRMWARE_UPGRADE_MODE)
>  		return;
>  
>  	sysfs_remove_link(&chip->dev.parent->kobj, "ppi");
> @@ -506,7 +508,8 @@ 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_FIRMWARE_UPGRADE_MODE)
>  		return 0;
>  
>  	rc = compat_only_sysfs_link_entry_to_kobj(
> @@ -536,7 +539,8 @@ 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_FIRMWARE_UPGRADE_MODE)
>  		return 0;
>  
>  	snprintf(chip->hwrng_name, sizeof(chip->hwrng_name),
> @@ -550,6 +554,9 @@ static int tpm_get_pcr_allocation(struct tpm_chip *chip)
>  {
>  	int rc;
>  
> +	if (chip->flags & TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE)
> +		return 0;
> +
>  	rc = (chip->flags & TPM_CHIP_FLAG_TPM2) ?
>  	     tpm2_get_pcr_allocation(chip) :
>  	     tpm1_get_pcr_allocation(chip);
> @@ -612,7 +619,7 @@ 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_FIRMWARE_UPGRADE_MODE))
>  		hwrng_unregister(&chip->hwrng);
>  out_ppi:
>  	tpm_bios_log_teardown(chip);
> @@ -637,10 +644,12 @@ 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_FIRMWARE_UPGRADE_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_FIRMWARE_UPGRADE_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..2842f3c667a5 100644
> --- a/drivers/char/tpm/tpm-sysfs.c
> +++ b/drivers/char/tpm/tpm-sysfs.c
> @@ -480,6 +480,9 @@ void tpm_sysfs_add_device(struct tpm_chip *chip)
>  
>  	WARN_ON(chip->groups_cnt != 0);
>  
> +	if (chip->flags & TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE)
> +		return;
> +
>  	if (chip->flags & TPM_CHIP_FLAG_TPM2)
>  		chip->groups[chip->groups_cnt++] = &tpm2_dev_group;
>  	else
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index a25815a6f625..76245c861e59 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 requires firmware upgrade\n");
> +		chip->flags |= TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE;
> +		rc = 0;
> +		goto out;
> +	} else if (rc && rc != TPM2_RC_INITIALIZE)
>  		goto out;
>  
>  	if (rc == TPM2_RC_INITIALIZE) {
> @@ -743,6 +748,13 @@ int tpm2_auto_startup(struct tpm_chip *chip)
>  	}
>  
>  	rc = tpm2_get_cc_attrs_tbl(chip);
> +	if (rc) {
> +		dev_info(&chip->dev,
> +			 "TPM requires firmware recovery/upgrade\n");

Why these two dev_info() messages differ?

You should put a single info message that is unconditionally printed
when in FW upgrade mode, and not sprikle bloat to fallback paths.

> +		chip->flags |= TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE;
> +		rc = 0;
> +		goto out;
> +	}
>  
>  out:
>  	if (rc > 0)
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index aa11fe323c56..498f487d786f 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_FIRMWARE_UPGRADE_MODE	= BIT(7),
>  };
>  
>  #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)

/Jarkko