Re: [PATCH v4 1/1] tpm: add sysfs exports for all banks of PCR registers

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, Aug 17, 2020 at 02:35:06PM -0700, James Bottomley wrote:
> Create sysfs per hash groups with 24 PCR files in them one group,
> named pcr-<hash>, for each agile hash of the TPM.  The files are
> plugged in to a PCR read function which is TPM version agnostic, so
> this works also for TPM 1.2 but the hash is only sha1 in that case.
> 
> Note: the macros used to create the hashes emit spurious checkpatch
> warnings.  Do not try to "fix" them as checkpatch recommends, otherwise
> they'll break.

"PCR access is required because IMA tools should be able to run without
any sort of TSS dependencies."

AFAIK, this is the only reason to merge this and it is missing from the
description. Perhaps you could either include that sentence, or
alternatively write something along the lines?

> 
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> Tested-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>

Please also cc this at least to Greg and Jason Gunthorpe next time.

> ---
> 
> v2: fix TPM 1.2 legacy links failure
> v3: fix warn on and add note to tpm_algorithms
> v4: reword commit and add tested-by
> ---
>  drivers/char/tpm/tpm-sysfs.c | 178 +++++++++++++++++++++++++++++++++++
>  include/linux/tpm.h          |   9 +-
>  2 files changed, 186 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c
> index d52bf4df0bca..81a02200b207 100644
> --- a/drivers/char/tpm/tpm-sysfs.c
> +++ b/drivers/char/tpm/tpm-sysfs.c
> @@ -348,11 +348,189 @@ static const struct attribute_group tpm2_dev_group = {
>  	.attrs = tpm2_dev_attrs,
>  };
>  
> +struct tpm_pcr_attr {
> +	int alg_id;
> +	int pcr;
> +	struct device_attribute attr;
> +};
> +
> +#define to_tpm_pcr_attr(a) container_of(a, struct tpm_pcr_attr, attr)
> +
> +static ssize_t pcr_value_show(struct device *dev,
> +			      struct device_attribute *attr,
> +			      char *buf)
> +{
> +	struct tpm_pcr_attr *ha = to_tpm_pcr_attr(attr);
> +	struct tpm_chip *chip = to_tpm_chip(dev);
> +	struct tpm_digest digest;
> +	int i;
> +	int digest_size = 0;
> +	int rc;
> +	char *str = buf;
> +
> +	for (i = 0; i < chip->nr_allocated_banks; i++)
> +		if (ha->alg_id == chip->allocated_banks[i].alg_id)
> +			digest_size = chip->allocated_banks[i].digest_size;
> +	/* should never happen */
> +	if (!digest_size)
> +		return -EINVAL;
> +
> +	digest.alg_id = ha->alg_id;
> +	rc = tpm_pcr_read(chip, ha->pcr, &digest);
> +	if (rc)
> +		return rc;
> +	for (i = 0; i < digest_size; i++)
> +		str += sprintf(str, "%02X", digest.digest[i]);
> +	str += sprintf(str, "\n");
> +
> +	return str - buf;
> +}
> +
> +/*
> + * The following set of defines represents all the magic to build
> + * the per hash attribute groups for displaying each bank of PCRs.
> + * The only slight problem with this approach is that every PCR is
> + * hard coded to be present, so you don't know if an PCR is missing
> + * until a cat of the file returns -EINVAL
> + *
> + * Also note you must ignore checkpatch warnings in this macro
> + * code. This is deep macro magic that checkpatch.pl doesn't
> + * understand.
> + */
> +
> +/* Note, this must match TPM2_PLATFORM_PCR which is fixed at 24. */
> +#define _TPM_HELPER(_alg, _hash, F) \
> +	F(_alg, _hash, 0)	    \
> +	F(_alg, _hash, 1)	    \
> +	F(_alg, _hash, 2)	    \
> +	F(_alg, _hash, 3)	    \
> +	F(_alg, _hash, 4)	    \
> +	F(_alg, _hash, 5)	    \
> +	F(_alg, _hash, 6)	    \
> +	F(_alg, _hash, 7)	    \
> +	F(_alg, _hash, 8)	    \
> +	F(_alg, _hash, 9)	    \
> +	F(_alg, _hash, 10)	    \
> +	F(_alg, _hash, 11)	    \
> +	F(_alg, _hash, 12)	    \
> +	F(_alg, _hash, 13)	    \
> +	F(_alg, _hash, 14)	    \
> +	F(_alg, _hash, 15)	    \
> +	F(_alg, _hash, 16)	    \
> +	F(_alg, _hash, 17)	    \
> +	F(_alg, _hash, 18)	    \
> +	F(_alg, _hash, 19)	    \
> +	F(_alg, _hash, 20)	    \
> +	F(_alg, _hash, 21)	    \
> +	F(_alg, _hash, 22)	    \
> +	F(_alg, _hash, 23)
> +
> +/* ignore checkpatch warning about trailing ; in macro. */
> +#define PCR_ATTR(_alg, _hash, _pcr)				   \
> +	static struct tpm_pcr_attr dev_attr_pcr_##_hash##_##_pcr = {	\
> +		.alg_id = _alg,					   \
> +		.pcr = _pcr,					   \
> +		.attr = {					   \
> +			.attr = {				   \
> +				.name = __stringify(_pcr),	   \
> +				.mode = 0444			   \
> +			},					   \
> +			.show = pcr_value_show			   \
> +		}						   \
> +	};
> +
> +#define PCR_ATTRS(_alg, _hash)			\
> +	_TPM_HELPER(_alg, _hash, PCR_ATTR)
> +
> +/* ignore checkpatch warning about trailing , in macro. */
> +#define PCR_ATTR_VAL(_alg, _hash, _pcr)		\
> +	&dev_attr_pcr_##_hash##_##_pcr.attr.attr,
> +
> +#define PCR_ATTR_GROUP_ARRAY(_alg, _hash)		       \
> +	static struct attribute *pcr_group_attrs_##_hash[] = { \
> +		_TPM_HELPER(_alg, _hash, PCR_ATTR_VAL)	       \
> +		NULL					       \
> +	}
> +
> +#define PCR_ATTR_GROUP(_alg, _hash)			    \
> +	static struct attribute_group pcr_group_##_hash = { \
> +		.name = "pcr-" __stringify(_hash),	    \
> +		.attrs = pcr_group_attrs_##_hash	    \
> +	}
> +
> +#define PCR_ATTR_BUILD(_alg, _hash)	   \
> +	PCR_ATTRS(_alg, _hash)		   \
> +	PCR_ATTR_GROUP_ARRAY(_alg, _hash); \
> +	PCR_ATTR_GROUP(_alg, _hash)
> +/*
> + * End of macro structure to build an attribute group containing 24
> + * PCR value files for each supported hash algorithm
> + */
> +
> +/*
> + * The next set of macros implements the cleverness for each hash to
> + * build a static attribute group called pcr_group_<hash> which can be
> + * added to chip->groups[].
> + *
> + * The first argument is the TPM algorithm id and the second is the
> + * hash used as both the suffix and the group name.  Note: the group
> + * name is a directory in the top level tpm class with the name
> + * pcr-<hash>, so it must not clash with any other names already
> + * in the sysfs directory.
> + */
> +PCR_ATTR_BUILD(TPM_ALG_SHA1, sha1);
> +PCR_ATTR_BUILD(TPM_ALG_SHA256, sha256);
> +PCR_ATTR_BUILD(TPM_ALG_SHA384, sha384);
> +PCR_ATTR_BUILD(TPM_ALG_SHA512, sha512);
> +PCR_ATTR_BUILD(TPM_ALG_SM3_256, sm3);
> +
> +
>  void tpm_sysfs_add_device(struct tpm_chip *chip)
>  {
> +	int i;
> +
>  	WARN_ON(chip->groups_cnt != 0);
> +
>  	if (chip->flags & TPM_CHIP_FLAG_TPM2)
>  		chip->groups[chip->groups_cnt++] = &tpm2_dev_group;
>  	else
>  		chip->groups[chip->groups_cnt++] = &tpm1_dev_group;
> +
> +	/* add one group for each bank hash */
> +	for (i = 0; i < chip->nr_allocated_banks; i++) {
> +		switch (chip->allocated_banks[i].alg_id) {
> +		case TPM_ALG_SHA1:
> +			chip->groups[chip->groups_cnt++] = &pcr_group_sha1;
> +			break;
> +		case TPM_ALG_SHA256:
> +			chip->groups[chip->groups_cnt++] = &pcr_group_sha256;
> +			break;
> +		case TPM_ALG_SHA384:
> +			chip->groups[chip->groups_cnt++] = &pcr_group_sha384;
> +			break;
> +		case TPM_ALG_SHA512:
> +			chip->groups[chip->groups_cnt++] = &pcr_group_sha512;
> +			break;
> +		case TPM_ALG_SM3_256:
> +			chip->groups[chip->groups_cnt++] = &pcr_group_sm3;
> +			break;
> +		default:
> +			/*
> +			 * If this warning triggers, send a patch to
> +			 * add both a PCR_ATTR_BUILD() macro above for
> +			 * the missing algorithm as well as an
> +			 * additional case in this switch statement.
> +			 */
> +			WARN(1, "TPM with unsupported bank algorthm 0x%04x",
> +			     chip->allocated_banks[i].alg_id);
> +			break;
> +		}
> +	}
> +
> +	/*
> +	 * This will only trigger if someone has added an additional
> +	 * hash to the tpm_algorithms enum without incrementing
> +	 * TPM_MAX_HASHES.
> +	 */
> +	WARN_ON(chip->groups_cnt > TPM_MAX_HASHES + 1);
>  }
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 3b5d455501c5..cc0b94dcf21e 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -31,6 +31,7 @@ struct tpm_chip;
>  struct trusted_key_payload;
>  struct trusted_key_options;
>  
> +/* if you add a new hash to this, increment TPM_MAX_HASHES below */
>  enum tpm_algorithms {
>  	TPM_ALG_ERROR		= 0x0000,
>  	TPM_ALG_SHA1		= 0x0004,
> @@ -42,6 +43,12 @@ enum tpm_algorithms {
>  	TPM_ALG_SM3_256		= 0x0012,
>  };
>  
> +/*
> + * maximum number of hashing algorithms a TPM can have.  This is
> + * basically a count of every hash in tpm_algorithms above
> + */
> +#define TPM_MAX_HASHES	5

This is an unnecessarly hard to maintain.

A better construction would be this.

enum tpm_alg_misc {
	TPM_ALG_ERROR		= 0x0000,
	TPM_ALG_KEYEDHASH	= 0x0008,
	TPM_ALG_NULL		= 0x0010,
}

enum tpm_alg_hash {
	TPM_ALG_SHA1		= 0x0004,
	TPM_ALG_SHA256		= 0x000B,
	TPM_ALG_SHA384		= 0x000C,
	TPM_ALG_SHA512		= 0x000D,
	TPM_ALG_SM3_256		= 0x0012,
	TPM_ALG_HASH_MAX,
};

> +
>  struct tpm_digest {
>  	u16 alg_id;
>  	u8 digest[TPM_MAX_DIGEST_SIZE];
> @@ -146,7 +153,7 @@ struct tpm_chip {
>  
>  	struct dentry *bios_dir[TPM_NUM_EVENT_LOG_FILES];
>  
> -	const struct attribute_group *groups[3];
> +	const struct attribute_group *groups[3 + TPM_MAX_HASHES];
>  	unsigned int groups_cnt;
>  
>  	u32 nr_allocated_banks;

/Jarkko