Re: [PATCH v4 1/6] tpm: dynamically allocate active_banks array

Roberto Sassu <roberto.sassu@xxxxxxxxxx> · Thu, 8 Nov 2018 15:40:17 +0100

On 11/8/2018 2:50 PM, Nayna Jain wrote:


On 11/07/2018 03:11 PM, Roberto Sassu wrote:
On 11/7/2018 7:14 AM, Nayna Jain wrote:


On 11/06/2018 08:31 PM, Roberto Sassu wrote:
This patch removes the hard-coded limit of the active_banks array size.


The hard-coded limit in static array active_banks[] represents the 
maximum possible banks.
A TPM might have three banks, but only one bank may be active.

To confirm my understanding, is the idea for this patch is to 
dynamically identify the number of possible banks or the number of 
active banks ?

The idea is to dynamically identify the number of active banks.

In the TPM Commands specification (section 30.2.1), I found:

TPM_CAP_PCRS – Returns the current allocation of PCR in a
TPML_PCR_SELECTION.

You mentioned:

#TPM_RC_SIZE response code when count is greater
than the possible number of banks

but TPML_PCR_SELECTION is provided by the TPM.

Based on a discussion with Ken, the count in the TPML_PCR_SELECTION 
returns the number of possible algorithms supported. In the example 
below, two possible algorithms - SHA1 and SHA256 - are returned.

# /usr/local/bin/tssgetcapability -cap 5
2 PCR selections
     hash TPM_ALG_SHA1
     TPMS_PCR_SELECTION length 3
     ff ff ff
     hash TPM_ALG_SHA256
     TPMS_PCR_SELECTION length 3
     00 00 00

The pcr_select fields - "ff ff ff" and "00 00 00" - are bit masks for 
the enabled PCRs. The SHA1 bank is enabled for all PCRs (0-23), while 
the SHA256 bank is not enabled.

The current code works, but it unnecessarily extends some banks. Instead 
of basing the number of active banks on the number of algorithms 
returned, it should be based on the pcr_select field.

Thanks. I will add a bank if at least one bit is set in the pcr_select
mask.

Roberto


    - Mimi & Nayna



Roberto


It stores in the tpm_chip structure the number of active PCR banks,
determined in tpm2_get_pcr_allocation(), and replaces the static array
with a pointer to a dynamically allocated array.

As a consequence of the introduction of nr_active_banks, 
tpm_pcr_extend()
does not check anymore if the algorithm stored in tpm_chip is equal to
zero. The active_banks array always contains valid algorithms.

Fixes: 1db15344f874 ("tpm: implement TPM 2.0 capability to get active
PCR banks")

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
  drivers/char/tpm/tpm-chip.c      |  1 +
  drivers/char/tpm/tpm-interface.c | 19 ++++++++++++-------
  drivers/char/tpm/tpm.h           |  3 ++-
  drivers/char/tpm/tpm2-cmd.c      | 17 ++++++++---------
  4 files changed, 23 insertions(+), 17 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 46caadca916a..2a9e8b744436 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -160,6 +160,7 @@ static void tpm_dev_release(struct device *dev)
      kfree(chip->log.bios_event_log);
      kfree(chip->work_space.context_buf);
      kfree(chip->work_space.session_buf);
+    kfree(chip->active_banks);
      kfree(chip);
  }

diff --git a/drivers/char/tpm/tpm-interface.c 
b/drivers/char/tpm/tpm-interface.c
index 1a803b0cf980..ba7ca6b3e664 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -1039,8 +1039,7 @@ static int tpm1_pcr_extend(struct tpm_chip 
*chip, int pcr_idx, const u8 *hash,
  int tpm_pcr_extend(struct tpm_chip *chip, int pcr_idx, const u8 
*hash)
  {
      int rc;
-    struct tpm2_digest digest_list[ARRAY_SIZE(chip->active_banks)];
-    u32 count = 0;
+    struct tpm2_digest *digest_list;
      int i;

      chip = tpm_find_get_ops(chip);
@@ -1048,16 +1047,22 @@ int tpm_pcr_extend(struct tpm_chip *chip, 
int pcr_idx, const u8 *hash)
          return -ENODEV;

      if (chip->flags & TPM_CHIP_FLAG_TPM2) {
-        memset(digest_list, 0, sizeof(digest_list));
+        digest_list = kmalloc_array(chip->nr_active_banks,
+                        sizeof(*digest_list), GFP_KERNEL);
+        if (!digest_list)
+            return -ENOMEM;

-        for (i = 0; i < ARRAY_SIZE(chip->active_banks) &&
-                chip->active_banks[i] != TPM2_ALG_ERROR; i++) {
+        memset(digest_list, 0,
+               chip->nr_active_banks * sizeof(*digest_list));
+
+        for (i = 0; i < chip->nr_active_banks; i++) {
              digest_list[i].alg_id = chip->active_banks[i];
              memcpy(digest_list[i].digest, hash, TPM_DIGEST_SIZE);
-            count++;
          }

-        rc = tpm2_pcr_extend(chip, pcr_idx, count, digest_list);
+        rc = tpm2_pcr_extend(chip, pcr_idx, chip->nr_active_banks,
+                     digest_list);
+        kfree(digest_list);
          tpm_put_ops(chip);
          return rc;
      }
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index f3501d05264f..98368c3a6ff7 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -248,7 +248,8 @@ struct tpm_chip {
      const struct attribute_group *groups[3];
      unsigned int groups_cnt;

-    u16 active_banks[7];
+    u32 nr_active_banks;
+    u16 *active_banks;
  #ifdef CONFIG_ACPI
      acpi_handle acpi_dev_handle;
      char ppi_version[TPM_PPI_VERSION_LEN + 1];
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index c31b490bd41d..533089cede07 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -242,7 +242,7 @@ int tpm2_pcr_extend(struct tpm_chip *chip, int 
pcr_idx, u32 count,
      int i;
      int j;

-    if (count > ARRAY_SIZE(chip->active_banks))
+    if (count > chip->nr_active_banks)
          return -EINVAL;

      rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND);
@@ -859,7 +859,6 @@ static ssize_t tpm2_get_pcr_allocation(struct 
tpm_chip *chip)
      void *marker;
      void *end;
      void *pcr_select_offset;
-    unsigned int count;
      u32 sizeof_pcr_selection;
      u32 rsp_len;
      int rc;
@@ -878,11 +877,14 @@ static ssize_t tpm2_get_pcr_allocation(struct 
tpm_chip *chip)
      if (rc)
          goto out;

-    count = be32_to_cpup(
+    chip->nr_active_banks = be32_to_cpup(
          (__be32 *)&buf.data[TPM_HEADER_SIZE + 5]);


As per my understanding, the count in the TPML_PCR_SELECTION 
represent the number of possible banks and not the number of active 
banks.
TCG Structures Spec for TPM 2.0 - Table 102 mentions this as 
explanation of #TPM_RC_SIZE.

Thanks & Regards,
     - Nayna



-    if (count > ARRAY_SIZE(chip->active_banks)) {
-        rc = -ENODEV;
+    chip->active_banks = kmalloc_array(chip->nr_active_banks,
+                       sizeof(*chip->active_banks),
+                       GFP_KERNEL);
+    if (!chip->active_banks) {
+        rc = -ENOMEM;
          goto out;
      }

@@ -891,7 +893,7 @@ static ssize_t tpm2_get_pcr_allocation(struct 
tpm_chip *chip)
      rsp_len = be32_to_cpup((__be32 *)&buf.data[2]);
      end = &buf.data[rsp_len];

-    for (i = 0; i < count; i++) {
+    for (i = 0; i < chip->nr_active_banks; i++) {
          pcr_select_offset = marker +
              offsetof(struct tpm2_pcr_selection, size_of_select);
          if (pcr_select_offset >= end) {
@@ -908,9 +910,6 @@ static ssize_t tpm2_get_pcr_allocation(struct 
tpm_chip *chip)
      }

  out:
-    if (i < ARRAY_SIZE(chip->active_banks))
-        chip->active_banks[i] = TPM2_ALG_ERROR;
-
      tpm_buf_destroy(&buf);

      return rc;




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