IMA: Define a new hook to measure the kexec boot command line arguments

Currently during soft reboot(kexec_file_load) boot command line
arguments are not measured. Define hooks needed to measure kexec
command line arguments during soft reboot(kexec_file_load).

- A new ima hook ima_kexec_cmdline is defined to be called by the
kexec code.
- A new function process_buffer_measurement is defined to measure
the buffer hash into the IMA measurement list.
- A new func policy KEXEC_CMDLINE is defined to control the
 measurement.

Signed-off-by: Prakhar Srivastava <prsriva02@gmail.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Documentation/ABI/testing/ima_policy

@@ -28,6 +28,7 @@ Description:
 		base: 	func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
 				[FIRMWARE_CHECK]
 				[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
+				[KEXEC_CMDLINE]
 			mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
 			       [[^]MAY_EXEC]
 			fsmagic:= hex value

include/linux/ima.h

@@ -26,6 +26,7 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
 extern void ima_post_path_mknod(struct dentry *dentry);
+extern void ima_kexec_cmdline(const void *buf, int size);
 
 #ifdef CONFIG_IMA_KEXEC
 extern void ima_add_kexec_buffer(struct kimage *image);
@@ -92,6 +93,7 @@ static inline void ima_post_path_mknod(struct dentry *dentry)
 	return;
 }
 
+static inline void ima_kexec_cmdline(const void *buf, int size) {}
 #endif /* CONFIG_IMA */
 
 #ifndef CONFIG_IMA_KEXEC

security/integrity/ima/ima.h

@@ -190,6 +190,7 @@ static inline unsigned long ima_hash_key(u8 *digest)
 	hook(KEXEC_KERNEL_CHECK)	\
 	hook(KEXEC_INITRAMFS_CHECK)	\
 	hook(POLICY_CHECK)		\
+	hook(KEXEC_CMDLINE)		\
 	hook(MAX_CHECK)
 #define __ima_hook_enumify(ENUM)	ENUM,
 

security/integrity/ima/ima_api.c

@@ -178,6 +178,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
  *		subj=, obj=, type=, func=, mask=, fsmagic=
  *	subj,obj, and type: are LSM specific.
  *	func: FILE_CHECK | BPRM_CHECK | CREDS_CHECK | MMAP_CHECK | MODULE_CHECK
+ *	| KEXEC_CMDLINE
  *	mask: contains the permission mask
  *	fsmagic: hex value
  *

security/integrity/ima/ima_main.c

@@ -609,6 +609,78 @@ int ima_load_data(enum kernel_load_data_id id)
 	return 0;
 }
 
+/*
+ * process_buffer_measurement - Measure the buffer to ima log.
+ * @buf: pointer to the buffer that needs to be added to the log.
+ * @size: size of buffer(in bytes).
+ * @eventname: event name to be used for the buffer entry.
+ * @cred: a pointer to a credentials structure for user validation.
+ * @secid: the secid of the task to be validated.
+ *
+ * Based on policy, the buffer is measured into the ima log.
+ */
+static void process_buffer_measurement(const void *buf, int size,
+				       const char *eventname,
+				       const struct cred *cred, u32 secid)
+{
+	int ret = 0;
+	struct ima_template_entry *entry = NULL;
+	struct integrity_iint_cache iint = {};
+	struct ima_event_data event_data = {.iint = &iint,
+					    .filename = eventname};
+	struct ima_template_desc *template_desc = NULL;
+	struct {
+		struct ima_digest_data hdr;
+		char digest[IMA_MAX_DIGEST_SIZE];
+	} hash = {};
+	int violation = 0;
+	int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
+	int action = 0;
+
+	action = ima_get_action(NULL, cred, secid, 0, KEXEC_CMDLINE, &pcr,
+				&template_desc);
+	if (!(action & IMA_MEASURE))
+		return;
+
+	iint.ima_hash = &hash.hdr;
+	iint.ima_hash->algo = ima_hash_algo;
+	iint.ima_hash->length = hash_digest_size[ima_hash_algo];
+
+	ret = ima_calc_buffer_hash(buf, size, iint.ima_hash);
+	if (ret < 0)
+		goto out;
+
+	ret = ima_alloc_init_template(&event_data, &entry, template_desc);
+	if (ret < 0)
+		goto out;
+
+	ret = ima_store_template(entry, violation, NULL, buf, pcr);
+
+	if (ret < 0)
+		ima_free_template_entry(entry);
+
+out:
+	return;
+}
+
+/**
+ * ima_kexec_cmdline - measure kexec cmdline boot args
+ * @buf: pointer to buffer
+ * @size: size of buffer
+ *
+ * Buffers can only be measured, not appraised.
+ */
+void ima_kexec_cmdline(const void *buf, int size)
+{
+	u32 secid;
+
+	if (buf && size != 0) {
+		security_task_getsecid(current, &secid);
+		process_buffer_measurement(buf, size, "kexec-cmdline",
+					   current_cred(), secid);
+	}
+}
+
 static int __init init_ima(void)
 {
 	int error;

security/integrity/ima/ima_policy.c

@@ -374,6 +374,11 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 {
 	int i;
 
+	if (func == KEXEC_CMDLINE) {
+		if ((rule->flags & IMA_FUNC) && (rule->func == func))
+			return true;
+		return false;
+	}
 	if ((rule->flags & IMA_FUNC) &&
 	    (rule->func != func && func != POST_SETATTR))
 		return false;
@@ -956,6 +961,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 				entry->func = KEXEC_INITRAMFS_CHECK;
 			else if (strcmp(args[0].from, "POLICY_CHECK") == 0)
 				entry->func = POLICY_CHECK;
+			else if (strcmp(args[0].from, "KEXEC_CMDLINE") == 0)
+				entry->func = KEXEC_CMDLINE;
 			else
 				result = -EINVAL;
 			if (!result)