linux-kernel - [PATCH v2 3/4] ima: Use tpm_chip_find() and access TPM functions using it

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Date:   Wed, 20 Jun 2018 16:42:35 -0400
From:   Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:     linux-integrity@...r.kernel.org, jarkko.sakkinen@...ux.intel.com,
        zohar@...ux.vnet.ibm.com
Cc:     jgg@...pe.ca, linux-kernel@...r.kernel.org,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>
Subject: [PATCH v2 3/4] ima: Use tpm_chip_find() and access TPM functions using it

Rather than accessing the TPM functions using a NULL pointer, which
causes a lookup for a suitable chip every time, get a hold of a tpm_chip
and access the TPM functions using this chip. We call the tpm_chip
ima_tpm_chip and protect it, once initialization is done, using a
rw_semaphore called ima_tpm_chip_lock.

Use ima_shutdown to release the tpm_chip.

Signed-off-by: Stefan Berger <stefanb@...ux.vnet.ibm.com>
---
 security/integrity/ima/ima.h        |  3 +++
 security/integrity/ima/ima_crypto.c | 12 ++++++++++--
 security/integrity/ima/ima_init.c   | 19 ++++++++++++-------
 security/integrity/ima/ima_queue.c  |  7 +++++--
 4 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 354bb5716ce3..53a88d578ca5 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -24,6 +24,7 @@
 #include <linux/hash.h>
 #include <linux/tpm.h>
 #include <linux/audit.h>
+#include <linux/rwsem.h>
 #include <crypto/hash_info.h>
 
 #include "../integrity.h"
@@ -56,6 +57,8 @@ extern int ima_policy_flag;
 extern int ima_used_chip;
 extern int ima_hash_algo;
 extern int ima_appraise;
+extern struct rw_semaphore ima_tpm_chip_lock;
+extern struct tpm_chip *ima_tpm_chip;
 
 /* IMA event related data */
 struct ima_event_data {
diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 4e085a17124f..da7715240476 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -631,10 +631,18 @@ int ima_calc_buffer_hash(const void *buf, loff_t len,
 
 static void __init ima_pcrread(int idx, u8 *pcr)
 {
+	int result = 0;
+
+	down_read(&ima_tpm_chip_lock);
+
 	if (!ima_used_chip)
-		return;
+		goto out;
+
+	result = tpm_pcr_read(ima_tpm_chip, idx, pcr);
+out:
+	up_read(&ima_tpm_chip_lock);
 
-	if (tpm_pcr_read(NULL, idx, pcr) != 0)
+	if (result != 0)
 		pr_err("Error Communicating to TPM chip\n");
 }
 
diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index 8a5258eb32b6..24db06c4f463 100644
--- a/security/integrity/ima/ima_init.c
+++ b/security/integrity/ima/ima_init.c
@@ -28,6 +28,8 @@
 /* name for boot aggregate entry */
 static const char *boot_aggregate_name = "boot_aggregate";
 int ima_used_chip;
+struct rw_semaphore ima_tpm_chip_lock = __RWSEM_INITIALIZER(ima_tpm_chip_lock);
+struct tpm_chip *ima_tpm_chip;
 
 /* Add the boot aggregate to the IMA measurement list and extend
  * the PCR register.
@@ -108,6 +110,13 @@ void __init ima_load_x509(void)
 static int ima_shutdown(struct notifier_block *this, unsigned long action,
 			void *data)
 {
+	down_write(&ima_tpm_chip_lock);
+	if (ima_tpm_chip) {
+		tpm_chip_put(ima_tpm_chip);
+		ima_tpm_chip = NULL;
+		ima_used_chip = 0;
+	}
+	up_write(&ima_tpm_chip_lock);
 	return NOTIFY_DONE;
 }
 
@@ -118,19 +127,15 @@ static struct notifier_block ima_reboot_notifier = {
 
 int __init ima_init(void)
 {
-	u8 pcr_i[TPM_DIGEST_SIZE];
 	int rc;
 
 	register_reboot_notifier(&ima_reboot_notifier);
 
-	ima_used_chip = 0;
-	rc = tpm_pcr_read(NULL, 0, pcr_i);
-	if (rc == 0)
-		ima_used_chip = 1;
+	ima_tpm_chip = tpm_chip_find();
 
+	ima_used_chip = (ima_tpm_chip != NULL);
 	if (!ima_used_chip)
-		pr_info("No TPM chip found, activating TPM-bypass! (rc=%d)\n",
-			rc);
+		pr_info("No TPM chip found, activating TPM-bypass!\n");
 
 	rc = integrity_init_keyring(INTEGRITY_KEYRING_IMA);
 	if (rc)
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 418f35e38015..6c9427939a28 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -142,10 +142,13 @@ static int ima_pcr_extend(const u8 *hash, int pcr)
 {
 	int result = 0;
 
+	down_read(&ima_tpm_chip_lock);
 	if (!ima_used_chip)
-		return result;
+		goto out;
 
-	result = tpm_pcr_extend(NULL, pcr, hash);
+	result = tpm_pcr_extend(ima_tpm_chip, pcr, hash);
+out:
+	up_read(&ima_tpm_chip_lock);
 	if (result != 0)
 		pr_err("Error Communicating to TPM chip, result: %d\n", result);
 	return result;
-- 
2.13.6