linux-kernel - Re: [PATCH v2] tpm: Add Upgrade/Reduced mode support for TPM2 modules

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Date:   Thu, 29 Jul 2021 00:58:19 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Borys Movchan <borysmn@...s.com>
Cc:     Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
        kernel@...s.com, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tpm: Add Upgrade/Reduced mode support for TPM2 modules

On Wed, Jul 28, 2021 at 12:57:30PM +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.
> 
> The fix adds the possibility to detect an active state of
> the TPM and gives the user-space a chance to finish the
> firmware upgrade/recover the TPM.

This is different than telling what the patch does. It's just
describing a goal, but does not describe how the driver is
changed, and reasons for doing that.

For instance, you check 'limited_mode' flag in a few sites.
How can I know that those are exactly the locations where this
needs to be done?

> Signed-off-by: Borys Movchan <borysmn@...s.com>
> ---
> 
> Notes:
>     v2: The terms are changed to match the ones used in the TPM specification.
>     Rework the commit message to provide more details regarding TPM
>     behavior in Failure/Upgrade mode.
> 
>     The TPM specification describes TPM behavior in Upgrade mode very clearly.
>     Things are a bit more complex if we are talking about Failure mode.
>     The TPM behavior in this mode is highly vendor-specific. Although, there
>     is one thing clearly described in the TPM specification and can be relied
>     on to detect the Failure state: in Failure mode, the TPM doesn't provide
>     any crypto operations. Including access to attributes and configuration
>     registers.
>     It seems persistent between different TPM manufacturers, at least to the
>     degree I was able to verify.
> 
>  drivers/char/tpm/tpm-chip.c | 23 +++++++++++++++--------
>  drivers/char/tpm/tpm2-cmd.c | 12 ++++++++++--
>  include/linux/tpm.h         |  1 +
>  3 files changed, 26 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index ddaeceb7e109..ff2367c447fb 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -574,20 +574,25 @@ static int tpm_get_pcr_allocation(struct tpm_chip *chip)
>  int tpm_chip_register(struct tpm_chip *chip)
>  {
>  	int rc;
> +	bool limited_mode = false;
>  
>  	rc = tpm_chip_start(chip);
>  	if (rc)
>  		return rc;
>  	rc = tpm_auto_startup(chip);
> -	if (rc) {
> +	if (rc == -EIO) {
> +		limited_mode = true;
> +	} else if (rc) {
>  		tpm_chip_stop(chip);
>  		return rc;
>  	}
>  
> -	rc = tpm_get_pcr_allocation(chip);
> -	tpm_chip_stop(chip);
> -	if (rc)
> -		return rc;
> +	if (!limited_mode) {
> +		rc = tpm_get_pcr_allocation(chip);
> +		tpm_chip_stop(chip);
> +		if (rc)
> +			return rc;
> +	}
>  
>  	tpm_sysfs_add_device(chip);
>  
> @@ -595,9 +600,11 @@ int tpm_chip_register(struct tpm_chip *chip)
>  
>  	tpm_add_ppi(chip);
>  
> -	rc = tpm_add_hwrng(chip);
> -	if (rc)
> -		goto out_ppi;
> +	if (!limited_mode) {
> +		rc = tpm_add_hwrng(chip);
> +		if (rc)
> +			goto out_ppi;
> +	}
>  
>  	rc = tpm_add_char_device(chip);
>  	if (rc)
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index a25815a6f625..7468353ed67d 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -718,7 +718,8 @@ static int tpm2_startup(struct tpm_chip *chip)
>   *                     sequence
>   * @chip: TPM chip to use
>   *
> - * Returns 0 on success, < 0 in case of fatal error.
> + * Returns 0 on success, -ENODEV in case of fatal error,
> + *	    -EIO in case of Reduced/Upgrade mode
>   */
>  int tpm2_auto_startup(struct tpm_chip *chip)
>  {
> @@ -729,7 +730,10 @@ 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) {
> +		rc = -EIO;
> +		goto out;
> +	} else if (rc && rc != TPM2_RC_INITIALIZE)
>  		goto out;
>  
>  	if (rc == TPM2_RC_INITIALIZE) {
> @@ -743,6 +747,10 @@ int tpm2_auto_startup(struct tpm_chip *chip)
>  	}
>  
>  	rc = tpm2_get_cc_attrs_tbl(chip);
> +	if (rc) { /* Succeeded until here, but failed -> reduced mode */
> +		rc = -EIO;
> +		goto out;
> +	}
>  
>  out:
>  	if (rc > 0)
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index aa11fe323c56..e873c42907f0 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,
> -- 
> 2.20.1
> 
> 

/Jarkko