[PATCH v3 0/1] add sysfs exports for TPM 2 PCR registers

[PATCH v3 0/1] add sysfs exports for TPM 2 PCR registers

[James Bottomley]

v3 corrects the WARN_ON check, adds a commet to tpm_algorithms and
adds Jerry's reviewed-by.

At last year's plumbers conference it was agreed in principle to
export TPM 2 PCRs via sysfs.  We also agreed we should conform to
sysfs rules of one value per file, which rules out the "pcrs" file
format of TPM 1.2 which has every PCR value in the same file.

I added these files using device groups, so one group per bank hash of
the TPM.  Using an emulator which supports a variety of hashes, you
can see the structure of the group files:

root@testdeb:~# ls -F /sys/class/tpm/tpm0/
dev      pcr-sha1/    pcr-sha384/  power/      tpm_version_major
device@  pcr-sha256/  pcr-sha512/  subsystem@  uevent

As a future enhancement, we could use the group is_visible function to
remove files corresponding to PCRs which don't exist.  The reason this
isn't present is that so far I've never seen a TPM with a missing PCR.

James

---

James Bottomley (1):
  tpm: add sysfs exports for all banks of PCR registers

 drivers/char/tpm/tpm-sysfs.c | 178 +++++++++++++++++++++++++++++++++++
 include/linux/tpm.h          |   9 +-
 2 files changed, 186 insertions(+), 1 deletion(-)

-- 
2.26.2

[PATCH v3 1/1] tpm: add sysfs exports for all banks of PCR registers

[James Bottomley]

use macro magic to create sysfs per hash groups with 24 PCR files in
them one for each possible agile hash of the TPM.  The files are
plugged in to a read function which is TPM version agnostic, so this
works also for TPM 1.2 although the hash is only sha1 in that case.
For every hash the TPM supports, a group named pcr-<hash> is created
and each of the PCR read files placed under it.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>

---

v2: fix TPM 1.2 legacy links failure
v3: fix warn on and add note to tpm_algorithms
---
 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 5026a06977e1..ce5120572e68 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
+
 struct tpm_digest {
 	u16 alg_id;
 	u8 digest[TPM_MAX_DIGEST_SIZE];
@@ -145,7 +152,7 @@ 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;
-- 
2.26.2

Re: [PATCH v3 1/1] tpm: add sysfs exports for all banks of PCR registers

[Jarkko Sakkinen]

On Wed, Jul 22, 2020 at 08:57:39AM -0700, James Bottomley wrote:
> use macro magic to create sysfs per hash groups with 24 PCR files in

'Use'

Please, just say what the patch does in plain English and dust the magic
away.

> them one for each possible agile hash of the TPM.  The files are
                                                   ~~

I'd prefer a single space.

> plugged in to a read function which is TPM version agnostic, so this
> works also for TPM 1.2 although the hash is only sha1 in that case.
> For every hash the TPM supports, a group named pcr-<hash> is created
> and each of the PCR read files placed under it.

Yeah, the commit message is missing the statement what it does and goes
straight away rationalizing "macro magic".

> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>

/Jarkko

Re: [PATCH v3 1/1] tpm: add sysfs exports for all banks of PCR registers

[James Bottomley]

On Fri, 2020-07-24 at 09:57 +0300, Jarkko Sakkinen wrote:
> On Wed, Jul 22, 2020 at 08:57:39AM -0700, James Bottomley wrote:
> > use macro magic to create sysfs per hash groups with 24 PCR files
> > in
> 
> 'Use'
> 
> Please, just say what the patch does in plain English and dust the
> magic away.

The reason for the macro magic comment is that there are 3 checkpatch
errors and one warning from this, all spurious, because checkpatch
doesn't understand the syntax of macros that create macros.

> > them one for each possible agile hash of the TPM.  The files are
>                                                    ~~
> 
> I'd prefer a single space.

It's still listed in the style guides as best practice for monospaced
fonts, but at this point I've lost the will to care about it.

> > plugged in to a read function which is TPM version agnostic, so
> > this works also for TPM 1.2 although the hash is only sha1 in that
> > case. For every hash the TPM supports, a group named pcr-<hash> is
> > created and each of the PCR read files placed under it.
> 
> Yeah, the commit message is missing the statement what it does and
> goes straight away rationalizing "macro magic".

OK so how about

---
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 although 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.
---

James

Re: [PATCH v3 1/1] tpm: add sysfs exports for all banks of PCR registers

[Thiago Jung Bauermann]

James Bottomley <James.Bottomley@HansenPartnership.com> writes:

> use macro magic to create sysfs per hash groups with 24 PCR files in
> them one for each possible agile hash of the TPM.  The files are
> plugged in to a read function which is TPM version agnostic, so this
> works also for TPM 1.2 although the hash is only sha1 in that case.
> For every hash the TPM supports, a group named pcr-<hash> is created
> and each of the PCR read files placed under it.
>
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>

I tested the patch on ppc64le, on the powernv platform:

Tested-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>

-- 
Thiago Jung Bauermann
IBM Linux Technology Center

Re: [PATCH v3 1/1] tpm: add sysfs exports for all banks of PCR registers

[Mimi Zohar]

Hi Jarkko,

On Sun, 2020-07-26 at 20:25 -0700, James Bottomley wrote:
> On Fri, 2020-07-24 at 09:57 +0300, Jarkko Sakkinen wrote:
> > On Wed, Jul 22, 2020 at 08:57:39AM -0700, James Bottomley wrote:
> > > use macro magic to create sysfs per hash groups with 24 PCR files
> > > in
> > 
> > 'Use'
> > 
> > Please, just say what the patch does in plain English and dust the
> > magic away.
> 
> The reason for the macro magic comment is that there are 3 checkpatch
> errors and one warning from this, all spurious, because checkpatch
> doesn't understand the syntax of macros that create macros.
> 
> > > them one for each possible agile hash of the TPM.  The files are
> >                                                    ~~
> > 
> > I'd prefer a single space.
> 
> It's still listed in the style guides as best practice for monospaced
> fonts, but at this point I've lost the will to care about it.
> 
> > > plugged in to a read function which is TPM version agnostic, so
> > > this works also for TPM 1.2 although the hash is only sha1 in that
> > > case. For every hash the TPM supports, a group named pcr-<hash> is
> > > created and each of the PCR read files placed under it.
> > 
> > Yeah, the commit message is missing the statement what it does and
> > goes straight away rationalizing "macro magic".
> 
> OK so how about
> 
> ---
> 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 although 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.
> ---

Any chance of getting this patch at least queued to be upstreamed?

thanks,

Mimi

Re: [PATCH v3 1/1] tpm: add sysfs exports for all banks of PCR registers

[Jarkko Sakkinen]

On Sun, Jul 26, 2020 at 08:25:39PM -0700, James Bottomley wrote:
> On Fri, 2020-07-24 at 09:57 +0300, Jarkko Sakkinen wrote:
> > On Wed, Jul 22, 2020 at 08:57:39AM -0700, James Bottomley wrote:
> > > use macro magic to create sysfs per hash groups with 24 PCR files
> > > in
> > 
> > 'Use'
> > 
> > Please, just say what the patch does in plain English and dust the
> > magic away.
> 
> The reason for the macro magic comment is that there are 3 checkpatch
> errors and one warning from this, all spurious, because checkpatch
> doesn't understand the syntax of macros that create macros.
> 
> > > them one for each possible agile hash of the TPM.  The files are
> >                                                    ~~
> > 
> > I'd prefer a single space.
> 
> It's still listed in the style guides as best practice for monospaced
> fonts, but at this point I've lost the will to care about it.
> 
> > > plugged in to a read function which is TPM version agnostic, so
> > > this works also for TPM 1.2 although the hash is only sha1 in that
> > > case. For every hash the TPM supports, a group named pcr-<hash> is
> > > created and each of the PCR read files placed under it.
> > 
> > Yeah, the commit message is missing the statement what it does and
> > goes straight away rationalizing "macro magic".
> 
> OK so how about
> 
> ---
> 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 although 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.
> ---
> 
> James
> 

I'll check the latest version (saw it in patchwork). I just came back
from vacation - sorry for the delay.

/Jarkko