[PATCH v8 04/10] ima: maintain memory size needed for serializing the measurement list

[Mimi Zohar]

In preparation for serializing the binary_runtime_measurements, this patch
maintains the amount of memory required.

Changelog v7:
- include the trailing null in the string length (reported by Dmitry Kasatkin)

Changelog v5:
- replace CONFIG_KEXEC_FILE with architecture CONFIG_HAVE_IMA_KEXEC (Thiago)

Changelog v3:
- include the ima_kexec_hdr size in the binary_runtime_measurement size.

Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
Acked-by: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>
---
 security/integrity/ima/Kconfig     | 12 +++++++++
 security/integrity/ima/ima.h       |  1 +
 security/integrity/ima/ima_queue.c | 53 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 5487827fa86c..370eb2f4dd37 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -27,6 +27,18 @@ config IMA
 	  to learn more about IMA.
 	  If unsure, say N.
 
+config IMA_KEXEC
+	bool "Enable carrying the IMA measurement list across a soft boot"
+	depends on IMA && TCG_TPM && HAVE_IMA_KEXEC
+	default n
+	help
+	   TPM PCRs are only reset on a hard reboot.  In order to validate
+	   a TPM's quote after a soft boot, the IMA measurement list of the
+	   running kernel must be saved and restored on boot.
+
+	   Depending on the IMA policy, the measurement list can grow to
+	   be very large.
+
 config IMA_MEASURE_PCR_IDX
 	int
 	depends on IMA
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 51dc8d57d64d..ea1dcc452911 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -143,6 +143,7 @@ void ima_print_digest(struct seq_file *m, u8 *digest, u32 size);
 struct ima_template_desc *ima_template_desc_current(void);
 int ima_restore_measurement_entry(struct ima_template_entry *entry);
 int ima_restore_measurement_list(loff_t bufsize, void *buf);
+unsigned long ima_get_binary_runtime_size(void);
 int ima_init_template(void);
 
 /*
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index e180de598a92..d9aa5ab71204 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -29,6 +29,11 @@
 #define AUDIT_CAUSE_LEN_MAX 32
 
 LIST_HEAD(ima_measurements);	/* list of all measurements */
+#ifdef CONFIG_IMA_KEXEC
+static unsigned long binary_runtime_size;
+#else
+static unsigned long binary_runtime_size = ULONG_MAX;
+#endif
 
 /* key: inode (before secure-hashing a file) */
 struct ima_h_table ima_htable = {
@@ -64,6 +69,24 @@ static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
 	return ret;
 }
 
+/*
+ * Calculate the memory required for serializing a single
+ * binary_runtime_measurement list entry, which contains a
+ * couple of variable length fields (e.g template name and data).
+ */
+static int get_binary_runtime_size(struct ima_template_entry *entry)
+{
+	int size = 0;
+
+	size += sizeof(u32);	/* pcr */
+	size += sizeof(entry->digest);
+	size += sizeof(int);	/* template name size field */
+	size += strlen(entry->template_desc->name) + 1;
+	size += sizeof(entry->template_data_len);
+	size += entry->template_data_len;
+	return size;
+}
+
 /* ima_add_template_entry helper function:
  * - Add template entry to the measurement list and hash table, for
  *   all entries except those carried across kexec.
@@ -91,9 +114,30 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 		key = ima_hash_key(entry->digest);
 		hlist_add_head_rcu(&qe->hnext, &ima_htable.queue[key]);
 	}
+
+	if (binary_runtime_size != ULONG_MAX) {
+		int size;
+
+		size = get_binary_runtime_size(entry);
+		binary_runtime_size = (binary_runtime_size < ULONG_MAX - size) ?
+		     binary_runtime_size + size : ULONG_MAX;
+	}
 	return 0;
 }
 
+/*
+ * Return the amount of memory required for serializing the
+ * entire binary_runtime_measurement list, including the ima_kexec_hdr
+ * structure.
+ */
+unsigned long ima_get_binary_runtime_size(void)
+{
+	if (binary_runtime_size >= (ULONG_MAX - sizeof(struct ima_kexec_hdr)))
+		return ULONG_MAX;
+	else
+		return binary_runtime_size + sizeof(struct ima_kexec_hdr);
+};
+
 static int ima_pcr_extend(const u8 *hash, int pcr)
 {
 	int result = 0;
@@ -107,8 +151,13 @@ static int ima_pcr_extend(const u8 *hash, int pcr)
 	return result;
 }
 
-/* Add template entry to the measurement list and hash table,
- * and extend the pcr.
+/*
+ * Add template entry to the measurement list and hash table, and
+ * extend the pcr.
+ *
+ * On systems which support carrying the IMA measurement list across
+ * kexec, maintain the total memory size required for serializing the
+ * binary_runtime_measurements.
  */
 int ima_add_template_entry(struct ima_template_entry *entry, int violation,
 			   const char *op, struct inode *inode,
-- 
2.1.0