Re: [PATCH v3 2/2] tpm: enhance TPM 2.0 PCR extend to support multiple banks

From: Nayna
Date: Fri Jan 13 2017 - 03:44:11 EST



On 01/12/2017 11:50 PM, Jarkko Sakkinen wrote:
On Thu, Jan 12, 2017 at 11:58:10AM -0500, Nayna Jain wrote:
The current TPM 2.0 device driver extends only the SHA1 PCR bank
but the TCG Specification[1] recommends extending all active PCR
banks, to prevent malicious users from setting unused PCR banks with
fake measurements and quoting them.

The existing in-kernel interface(tpm_pcr_extend()) expects only a
SHA1 digest. To extend all active PCR banks with differing
digest sizes, the SHA1 digest is padded with trailing 0's as needed.

[1] TPM 2.0 Specification referred here is "TCG PC Client Specific
Platform Firmware Profile for TPM 2.0"

Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>
---
drivers/char/tpm/Kconfig | 1 +
drivers/char/tpm/tpm-interface.c | 16 +++++++++-
drivers/char/tpm/tpm.h | 3 +-
drivers/char/tpm/tpm2-cmd.c | 68 +++++++++++++++++++++++-----------------
drivers/char/tpm/tpm_eventlog.h | 18 +++++++++++
5 files changed, 75 insertions(+), 31 deletions(-)

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index 277186d..af985cc 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -6,6 +6,7 @@ menuconfig TCG_TPM
tristate "TPM Hardware Support"
depends on HAS_IOMEM
select SECURITYFS
+ select CRYPTO_HASH_INFO

In the commit message you did not mention this.

---help---
If you have a TPM security chip in your system, which
implements the Trusted Computing Group's specification,
diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index fecdd3f..e037dd2 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -7,6 +7,7 @@
* Dave Safford <safford@xxxxxxxxxxxxxx>
* Reiner Sailer <sailer@xxxxxxxxxxxxxx>
* Kylene Hall <kjhall@xxxxxxxxxx>
+ * Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>

Remove.

*
* Maintained by: <tpmdd-devel@xxxxxxxxxxxxxxxxxxxxx>
*
@@ -759,6 +760,7 @@ static const struct tpm_input_header pcrextend_header = {
int tpm_pcr_extend(u32 chip_num, int pcr_idx, const u8 *hash)
{
struct tpm_cmd_t cmd;
+ int i;
int rc;
struct tpm_chip *chip;

@@ -767,7 +769,19 @@ int tpm_pcr_extend(u32 chip_num, int pcr_idx, const u8 *hash)
return -ENODEV;

if (chip->flags & TPM_CHIP_FLAG_TPM2) {
- rc = tpm2_pcr_extend(chip, pcr_idx, hash);
+ struct tpml_digest_values d_values;
+
+ memset(&d_values, 0, sizeof(d_values));
+
+ for (i = 0; (chip->active_banks[i] != 0) &&
+ (i < ARRAY_SIZE(chip->active_banks)); i++) {
+ d_values.digests[i].alg_id = chip->active_banks[i];
+ memcpy(d_values.digests[i].digest, hash,
+ TPM_DIGEST_SIZE);
+ d_values.count++;
+ }
+
+ rc = tpm2_pcr_extend(chip, pcr_idx, &d_values);
tpm_put_ops(chip);
return rc;
}
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index dddd573..dd82d58 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -533,7 +533,8 @@ static inline void tpm_add_ppi(struct tpm_chip *chip)
#endif

int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u8 *res_buf);
-int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, const u8 *hash);
+int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx,
+ struct tpml_digest_values *digests);
int tpm2_get_random(struct tpm_chip *chip, u8 *out, size_t max);
int tpm2_seal_trusted(struct tpm_chip *chip,
struct trusted_key_payload *payload,
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 87388921..5027a54 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -64,9 +64,7 @@ struct tpm2_pcr_extend_in {
__be32 pcr_idx;
__be32 auth_area_size;
struct tpm2_null_auth_area auth_area;
- __be32 digest_cnt;
- __be16 hash_alg;
- u8 digest[TPM_DIGEST_SIZE];
+ struct tpml_digest_values digests;
} __packed;

struct tpm2_get_tpm_pt_in {
@@ -296,46 +294,58 @@ int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u8 *res_buf)
return rc;
}

-#define TPM2_GET_PCREXTEND_IN_SIZE \
- (sizeof(struct tpm_input_header) + \
- sizeof(struct tpm2_pcr_extend_in))
-
-static const struct tpm_input_header tpm2_pcrextend_header = {
- .tag = cpu_to_be16(TPM2_ST_SESSIONS),
- .length = cpu_to_be32(TPM2_GET_PCREXTEND_IN_SIZE),
- .ordinal = cpu_to_be32(TPM2_CC_PCR_EXTEND)
-};
-
/**
* tpm2_pcr_extend() - extend a PCR value
*
* @chip: TPM chip to use.
* @pcr_idx: index of the PCR.
- * @hash: hash value to use for the extend operation.
+ * @digests: list of pcr banks and corresponding hash values to be extended.
*
* Return: Same as with tpm_transmit_cmd.
*/
-int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, const u8 *hash)
+int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx,
+ struct tpml_digest_values *digests)
{
- struct tpm2_cmd cmd;
+ struct tpm_buf buf;
+ struct tpm2_null_auth_area auth_area;
int rc;
+ int i;
+ int j;

- cmd.header.in = tpm2_pcrextend_header;
- cmd.params.pcrextend_in.pcr_idx = cpu_to_be32(pcr_idx);
- cmd.params.pcrextend_in.auth_area_size =
- cpu_to_be32(sizeof(struct tpm2_null_auth_area));
- cmd.params.pcrextend_in.auth_area.handle =
- cpu_to_be32(TPM2_RS_PW);
- cmd.params.pcrextend_in.auth_area.nonce_size = 0;
- cmd.params.pcrextend_in.auth_area.attributes = 0;
- cmd.params.pcrextend_in.auth_area.auth_size = 0;
- cmd.params.pcrextend_in.digest_cnt = cpu_to_be32(1);
- cmd.params.pcrextend_in.hash_alg = cpu_to_be16(TPM2_ALG_SHA1);
- memcpy(cmd.params.pcrextend_in.digest, hash, TPM_DIGEST_SIZE);
+ rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND);
+ if (rc)
+ return rc;

- rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0,
+ 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));
+ tpm_buf_append_u32(&buf, digests->count);
+
+ for (i = 0; i < digests->count; i++) {
+ for (j = 0; j < ARRAY_SIZE(tpm2_hash_map); j++) {
+ if (digests->digests[i].alg_id !=
+ tpm2_hash_map[j].tpm_id)
+ continue;
+
+ tpm_buf_append_u16(&buf, digests->digests[i].alg_id);
+ tpm_buf_append(&buf, (const unsigned char
+ *)&digests->digests[i].digest,
+ hash_digest_size[tpm2_hash_map[j].crypto_id]);
+ }
+ }
+
+ rc = tpm_transmit_cmd(chip, buf.data, tpm_buf_length(&buf), 0,
"attempting extend a PCR value");

+ tpm_buf_destroy(&buf);
+
return rc;
}

diff --git a/drivers/char/tpm/tpm_eventlog.h b/drivers/char/tpm/tpm_eventlog.h
index 1660d74..2e47f4d 100644
--- a/drivers/char/tpm/tpm_eventlog.h
+++ b/drivers/char/tpm/tpm_eventlog.h
@@ -2,9 +2,12 @@
#ifndef __TPM_EVENTLOG_H__
#define __TPM_EVENTLOG_H__

+#include <crypto/hash_info.h>
+
#define TCG_EVENT_NAME_LEN_MAX 255
#define MAX_TEXT_EVENT 1000 /* Max event string length */
#define ACPI_TCPA_SIG "TCPA" /* 0x41504354 /'TCPA' */
+#define TPM2_ACTIVE_PCR_BANKS 3

#ifdef CONFIG_PPC64
#define do_endian_conversion(x) be32_to_cpu(x)
@@ -73,6 +76,21 @@ enum tcpa_pc_event_ids {
HOST_TABLE_OF_DEVICES,
};

+/**
+ * Digest structures for TPM 2.0 as defined in document
+ * Trusted Platform Module Library Part 2: Structures, Family "2.0".
+ */

Please remove this comment

+
+struct tpmt_ha {
+ u16 alg_id;
+ u8 digest[SHA384_DIGEST_SIZE];
+} __packed;

struct tpm2_hash

+struct tpml_digest_values {
+ u32 count;
+ struct tpmt_ha digests[TPM2_ACTIVE_PCR_BANKS];
+} __packed;

Please remove this structure.

Sorry Jarkko, I didn't understand this comment.
Why do we want to remove this structure.

Thanks & Regards,
- Nayna


+
#if defined(CONFIG_ACPI)
int tpm_read_log_acpi(struct tpm_chip *chip);
#else
--
2.5.0


/Jarkko