[PATCH 04/10] ima: implement functions to suspend and resume measurements

[Tushar Sugandhi]

The IMA subsystem needs to provide a mechanism to suspend or resume
measurements.  This functionality is needed to temporarily halt the
recording of IMA measurements during certain system operations.

Add functions ima_measurements_suspend() and ima_measurements_resume()
functions to set and reset the suspend_ima_measurements variable,
respectively, to suspend/resume IMA measurements.  Use
ima_extend_list_mutex to ensure that the operations are thread-safe.

Note: Use ima_measurements_suspend() and ima_measurements_resume() in
pairs to avoid indefinitely suspending IMA measurements.

Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
---
 security/integrity/ima/ima.h       |  2 ++
 security/integrity/ima/ima_queue.c | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 2ffda9449b9b..7127c5cf1909 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -163,6 +163,8 @@ bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
 int ima_restore_measurement_entry(struct ima_template_entry *entry);
 int ima_restore_measurement_list(loff_t bufsize, void *buf);
 int ima_measurements_show(struct seq_file *m, void *v);
+void ima_measurements_suspend(void);
+void ima_measurements_resume(void);
 unsigned long ima_get_binary_runtime_size(void);
 int ima_init_template(void);
 void ima_init_template_list(void);
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 532da87ce519..cb9abc02a304 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -44,6 +44,11 @@ struct ima_h_table ima_htable = {
  */
 static DEFINE_MUTEX(ima_extend_list_mutex);
 
+/*
+ * Used internally by the kernel to suspend-resume ima measurements.
+ */
+static atomic_t suspend_ima_measurements;
+
 /* lookup up the digest value in the hash table, and return the entry */
 static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
 						       int pcr)
@@ -148,6 +153,20 @@ static int ima_pcr_extend(struct tpm_digest *digests_arg, int pcr)
 	return result;
 }
 
+void ima_measurements_suspend(void)
+{
+	mutex_lock(&ima_extend_list_mutex);
+	atomic_set(&suspend_ima_measurements, 1);
+	mutex_unlock(&ima_extend_list_mutex);
+}
+
+void ima_measurements_resume(void)
+{
+	mutex_lock(&ima_extend_list_mutex);
+	atomic_set(&suspend_ima_measurements, 0);
+	mutex_unlock(&ima_extend_list_mutex);
+}
+
 /*
  * Add template entry to the measurement list and hash table, and
  * extend the pcr.
-- 
2.25.1