Re: [PATCH v5 01/11] tpm: Add support for in-kernel resetting of PCRs

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Nov 11, 2022 at 03:16:26PM -0800, Evan Green wrote:
> Add an internal command for resetting a PCR. This will be used by the
> encrypted hibernation code to set PCR23 to a known value. The
> hibernation code will seal the hibernation key with a policy specifying
> PCR23 be set to this known value as a mechanism to ensure that the
> hibernation key is genuine. But to do this repeatedly, resetting the PCR
> is necessary as well.
> 
> Link: https://lore.kernel.org/lkml/20210220013255.1083202-2-matthewgarrett@google.com/
> Co-developed-by: Matthew Garrett <mjg59@google.com>
> Signed-off-by: Matthew Garrett <mjg59@google.com>
> Signed-off-by: Evan Green <evgreen@chromium.org>
> 
> ---
> 
> Changes in v5:
>  - Change to co-developed by Matthew (Kees)
> 
> Changes in v4:
>  - Open code tpm2_pcr_reset implementation in tpm-interface.c (Jarkko)
>  - Rename interface symbol to tpm2_pcr_reset, fix kerneldocs (Jarkko)
> 
> Changes in v3:
>  - Unify tpm1/2_pcr_reset prototypes (Jarkko)
>  - Wait no, remove the TPM1 stuff altogether (Jarkko)
>  - Remove extra From tag and blank in commit msg (Jarkko).
> 
>  drivers/char/tpm/tpm-interface.c | 47 ++++++++++++++++++++++++++++++++
>  drivers/char/tpm/tpm2-cmd.c      |  7 -----
>  include/linux/tpm.h              | 14 ++++++++++
>  3 files changed, 61 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 1621ce8187052c..886277b2654e3b 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -342,6 +342,53 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
>  }
>  EXPORT_SYMBOL_GPL(tpm_pcr_extend);
>  
> +/**
> + * tpm2_pcr_reset - Reset the specified PCR
> + * @chip: A &struct tpm_chip instance, %NULL for the default chip
> + * @pcr_idx: The PCR to be reset
> + *
> + * Return: Same as with tpm_transmit_cmd(), or ENOTTY for TPM1 devices.
> + */
> +int tpm2_pcr_reset(struct tpm_chip *chip, u32 pcr_idx)
> +{
> +	struct tpm2_null_auth_area auth_area;
> +	struct tpm_buf buf;
> +	int rc;
> +
> +	chip = tpm_find_get_ops(chip);
> +	if (!chip)
> +		return -ENODEV;
> +
> +	if (!(chip->flags & TPM_CHIP_FLAG_TPM2)) {
> +		rc = -ENOTTY;
> +		goto out;
> +	}
> +
> +	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_RESET);
> +	if (rc)
> +		goto out;
> +
> +	tpm_buf_append_u32(&buf, pcr_idx);
> +
> +	auth_area.handle = cpu_to_be32(TPM2_RS_PW);
> +	auth_area.nonce_size = 0;
> +	auth_area.attributes = 0;
> +	auth_area.auth_size = 0;
> +
> +	tpm_buf_append_u32(&buf, sizeof(struct tpm2_null_auth_area));
> +	tpm_buf_append(&buf, (const unsigned char *)&auth_area,
> +		       sizeof(auth_area));
> +
> +	rc = tpm_transmit_cmd(chip, &buf, 0, "attempting to reset a PCR");
> +
> +	tpm_buf_destroy(&buf);
> +
> +out:
> +	tpm_put_ops(chip);
> +	return rc;
> +}
> +EXPORT_SYMBOL_GPL(tpm2_pcr_reset);
> +
>  /**
>   * tpm_send - send a TPM command
>   * @chip:	a &struct tpm_chip instance, %NULL for the default chip
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index 65d03867e114c5..303ce2ea02a4b0 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -216,13 +216,6 @@ int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
>  	return rc;
>  }
>  
> -struct tpm2_null_auth_area {
> -	__be32  handle;
> -	__be16  nonce_size;
> -	u8  attributes;
> -	__be16  auth_size;
> -} __packed;
> -
>  /**
>   * tpm2_pcr_extend() - extend a PCR value
>   *
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index dfeb25a0362dee..70134e6551745f 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -219,6 +219,7 @@ enum tpm2_command_codes {
>  	TPM2_CC_HIERARCHY_CONTROL       = 0x0121,
>  	TPM2_CC_HIERARCHY_CHANGE_AUTH   = 0x0129,
>  	TPM2_CC_CREATE_PRIMARY          = 0x0131,
> +	TPM2_CC_PCR_RESET		= 0x013D,
>  	TPM2_CC_SEQUENCE_COMPLETE       = 0x013E,
>  	TPM2_CC_SELF_TEST	        = 0x0143,
>  	TPM2_CC_STARTUP		        = 0x0144,
> @@ -293,6 +294,13 @@ struct tpm_header {
>  	};
>  } __packed;
>  
> +struct tpm2_null_auth_area {
> +	__be32  handle;
> +	__be16  nonce_size;
> +	u8  attributes;
> +	__be16  auth_size;
> +} __packed;
> +
>  /* A string buffer type for constructing TPM commands. This is based on the
>   * ideas of string buffer code in security/keys/trusted.h but is heap based
>   * in order to keep the stack usage minimal.
> @@ -423,6 +431,7 @@ extern ssize_t tpm_transmit_cmd(struct tpm_chip *chip, struct tpm_buf *buf,
>  				size_t min_rsp_body_length, const char *desc);
>  extern int tpm_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
>  			struct tpm_digest *digest);
> +extern int tpm2_pcr_reset(struct tpm_chip *chip, u32 pcr_idx);
>  extern int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
>  			  struct tpm_digest *digests);
>  extern int tpm_send(struct tpm_chip *chip, void *cmd, size_t buflen);
> @@ -440,6 +449,11 @@ static inline int tpm_pcr_read(struct tpm_chip *chip, int pcr_idx,
>  	return -ENODEV;
>  }
>  
> +static inline int tpm2_pcr_reset(struct tpm_chip *chip, int pcr_idx)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
>  				 struct tpm_digest *digests)
>  {
> -- 
> 2.38.1.431.g37b22c650d-goog
> 

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko