kprobes: improve error handling when arming/disarming kprobes

index b4aab48ad258..21d88cebb29b 100644
@@ -988,18 +988,32 @@ static int prepare_kprobe(struct kprobe *p)
 }
 
 /* Caller must lock kprobe_mutex */
-static void arm_kprobe_ftrace(struct kprobe *p)
+static int arm_kprobe_ftrace(struct kprobe *p)
 {
-	int ret;
+	int ret = 0;
 
 	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
 				   (unsigned long)p->addr, 0, 0);
-	WARN(ret < 0, "Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, ret);
-	kprobe_ftrace_enabled++;
-	if (kprobe_ftrace_enabled == 1) {
+	if (WARN(ret < 0, "Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, ret))
+		return ret;
+
+	if (kprobe_ftrace_enabled == 0) {
 		ret = register_ftrace_function(&kprobe_ftrace_ops);
-		WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret);
+		if (WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret))
+			goto err_ftrace;
 	}
+
+	kprobe_ftrace_enabled++;
+	return ret;
+
+err_ftrace:
+	/*
+	 * Note: Since kprobe_ftrace_ops has IPMODIFY set, and ftrace requires a
+	 * non-empty filter_hash for IPMODIFY ops, we're safe from an accidental
+	 * empty filter_hash which would undesirably trace all functions.
+	 */
+	ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0);
+	return ret;
 }
 
 /* Caller must lock kprobe_mutex */

@@ -1018,22 +1032,23 @@ static void disarm_kprobe_ftrace(struct kprobe *p)
 }
 #else	/* !CONFIG_KPROBES_ON_FTRACE */
 #define prepare_kprobe(p)	arch_prepare_kprobe(p)
-#define arm_kprobe_ftrace(p)	do {} while (0)
+#define arm_kprobe_ftrace(p)	(-ENODEV)
 #define disarm_kprobe_ftrace(p)	do {} while (0)
 #endif
 
 /* Arm a kprobe with text_mutex */
-static void arm_kprobe(struct kprobe *kp)
+static int arm_kprobe(struct kprobe *kp)
 {
-	if (unlikely(kprobe_ftrace(kp))) {
-		arm_kprobe_ftrace(kp);
-		return;
-	}
+	if (unlikely(kprobe_ftrace(kp)))
+		return arm_kprobe_ftrace(kp);
+
 	cpus_read_lock();
 	mutex_lock(&text_mutex);
 	__arm_kprobe(kp);
 	mutex_unlock(&text_mutex);
 	cpus_read_unlock();
+
+	return 0;
 }
 
 /* Disarm a kprobe with text_mutex */

@@ -1372,9 +1387,15 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
 
 	if (ret == 0 && kprobe_disabled(ap) && !kprobe_disabled(p)) {
 		ap->flags &= ~KPROBE_FLAG_DISABLED;
-		if (!kprobes_all_disarmed)
+		if (!kprobes_all_disarmed) {
 			/* Arm the breakpoint again. */
-			arm_kprobe(ap);
+			ret = arm_kprobe(ap);
+			if (ret) {
+				ap->flags |= KPROBE_FLAG_DISABLED;
+				list_del_rcu(&p->list);
+				synchronize_sched();
+			}
+		}
 	}
 	return ret;
 }

@@ -1594,8 +1615,14 @@ int register_kprobe(struct kprobe *p)
 	hlist_add_head_rcu(&p->hlist,
 		       &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 
-	if (!kprobes_all_disarmed && !kprobe_disabled(p))
-		arm_kprobe(p);
+	if (!kprobes_all_disarmed && !kprobe_disabled(p)) {
+		ret = arm_kprobe(p);
+		if (ret) {
+			hlist_del_rcu(&p->hlist);
+			synchronize_sched();
+			goto out;
+		}
+	}
 
 	/* Try to optimize kprobe */
 	try_to_optimize_kprobe(p);

@@ -2137,7 +2164,9 @@ int enable_kprobe(struct kprobe *kp)
 
 	if (!kprobes_all_disarmed && kprobe_disabled(p)) {
 		p->flags &= ~KPROBE_FLAG_DISABLED;
-		arm_kprobe(p);
+		ret = arm_kprobe(p);
+		if (ret)
+			p->flags |= KPROBE_FLAG_DISABLED;
 	}
 out:
 	mutex_unlock(&kprobe_mutex);

@@ -2565,11 +2594,12 @@ static const struct file_operations debugfs_kprobe_ei_ops = {
 	.release        = seq_release,
 };
 
-static void arm_all_kprobes(void)
+static int arm_all_kprobes(void)
 {
 	struct hlist_head *head;
 	struct kprobe *p;
-	unsigned int i;
+	unsigned int i, total = 0, errors = 0;
+	int err, ret = 0;
 
 	mutex_lock(&kprobe_mutex);
 

@@ -2586,16 +2616,28 @@ static void arm_all_kprobes(void)
 	/* Arming kprobes doesn't optimize kprobe itself */
 	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 		head = &kprobe_table[i];
-		hlist_for_each_entry_rcu(p, head, hlist)
-			if (!kprobe_disabled(p))
-				arm_kprobe(p);
+		/* Arm all kprobes on a best-effort basis */
+		hlist_for_each_entry_rcu(p, head, hlist) {
+			if (!kprobe_disabled(p)) {
+				err = arm_kprobe(p);
+				if (err)  {
+					errors++;
+					ret = err;
+				}
+				total++;
+			}
+		}
 	}
 
-	printk(KERN_INFO "Kprobes globally enabled\n");
+	if (errors)
+		pr_warn("Kprobes globally enabled, but failed to arm %d out of %d probes\n",
+			errors, total);
+	else
+		pr_info("Kprobes globally enabled\n");
 
 already_enabled:
 	mutex_unlock(&kprobe_mutex);
-	return;
+	return ret;
 }
 
 static void disarm_all_kprobes(void)

@@ -2652,6 +2694,7 @@ static ssize_t write_enabled_file_bool(struct file *file,
 {
 	char buf[32];
 	size_t buf_size;
+	int ret = 0;
 
 	buf_size = min(count, (sizeof(buf)-1));
 	if (copy_from_user(buf, user_buf, buf_size))

@@ -2662,7 +2705,7 @@ static ssize_t write_enabled_file_bool(struct file *file,
 	case 'y':
 	case 'Y':
 	case '1':
-		arm_all_kprobes();
+		ret = arm_all_kprobes();
 		break;
 	case 'n':
 	case 'N':

@@ -2673,6 +2716,9 @@ static ssize_t write_enabled_file_bool(struct file *file,
 		return -EINVAL;
 	}
 
+	if (ret)
+		return ret;
+
 	return count;
 }
 

index 21d88cebb29b..2792450b811e 100644
@@ -1017,23 +1017,27 @@ static int arm_kprobe_ftrace(struct kprobe *p)
 }
 
 /* Caller must lock kprobe_mutex */
-static void disarm_kprobe_ftrace(struct kprobe *p)
+static int disarm_kprobe_ftrace(struct kprobe *p)
 {
-	int ret;
+	int ret = 0;
 
-	kprobe_ftrace_enabled--;
-	if (kprobe_ftrace_enabled == 0) {
+	if (kprobe_ftrace_enabled == 1) {
 		ret = unregister_ftrace_function(&kprobe_ftrace_ops);
-		WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret);
+		if (WARN(ret < 0, "Failed to unregister kprobe-ftrace (%d)\n", ret))
+			return ret;
 	}
+
+	kprobe_ftrace_enabled--;
+
 	ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
 			   (unsigned long)p->addr, 1, 0);
 	WARN(ret < 0, "Failed to disarm kprobe-ftrace at %p (%d)\n", p->addr, ret);
+	return ret;
 }
 #else	/* !CONFIG_KPROBES_ON_FTRACE */
 #define prepare_kprobe(p)	arch_prepare_kprobe(p)
 #define arm_kprobe_ftrace(p)	(-ENODEV)
-#define disarm_kprobe_ftrace(p)	do {} while (0)
+#define disarm_kprobe_ftrace(p)	(-ENODEV)
 #endif
 
 /* Arm a kprobe with text_mutex */

@@ -1052,18 +1056,18 @@ static int arm_kprobe(struct kprobe *kp)
 }
 
 /* Disarm a kprobe with text_mutex */
-static void disarm_kprobe(struct kprobe *kp, bool reopt)
+static int disarm_kprobe(struct kprobe *kp, bool reopt)
 {
-	if (unlikely(kprobe_ftrace(kp))) {
-		disarm_kprobe_ftrace(kp);
-		return;
-	}
+	if (unlikely(kprobe_ftrace(kp)))
+		return disarm_kprobe_ftrace(kp);
 
 	cpus_read_lock();
 	mutex_lock(&text_mutex);
 	__disarm_kprobe(kp, reopt);
 	mutex_unlock(&text_mutex);
 	cpus_read_unlock();
+
+	return 0;
 }
 
 /*

@@ -1656,11 +1660,12 @@ static int aggr_kprobe_disabled(struct kprobe *ap)
 static struct kprobe *__disable_kprobe(struct kprobe *p)
 {
 	struct kprobe *orig_p;
+	int ret;
 
 	/* Get an original kprobe for return */
 	orig_p = __get_valid_kprobe(p);
 	if (unlikely(orig_p == NULL))
-		return NULL;
+		return ERR_PTR(-EINVAL);
 
 	if (!kprobe_disabled(p)) {
 		/* Disable probe if it is a child probe */

@@ -1674,8 +1679,13 @@ static struct kprobe *__disable_kprobe(struct kprobe *p)
 			 * should have already been disarmed, so
 			 * skip unneed disarming process.
 			 */
-			if (!kprobes_all_disarmed)
-				disarm_kprobe(orig_p, true);
+			if (!kprobes_all_disarmed) {
+				ret = disarm_kprobe(orig_p, true);
+				if (ret) {
+					p->flags &= ~KPROBE_FLAG_DISABLED;
+					return ERR_PTR(ret);
+				}
+			}
 			orig_p->flags |= KPROBE_FLAG_DISABLED;
 		}
 	}

@@ -1692,8 +1702,8 @@ static int __unregister_kprobe_top(struct kprobe *p)
 
 	/* Disable kprobe. This will disarm it if needed. */
 	ap = __disable_kprobe(p);
-	if (ap == NULL)
-		return -EINVAL;
+	if (IS_ERR(ap))
+		return PTR_ERR(ap);
 
 	if (ap == p)
 		/*

@@ -2126,12 +2136,14 @@ static void kill_kprobe(struct kprobe *p)
 int disable_kprobe(struct kprobe *kp)
 {
 	int ret = 0;
+	struct kprobe *p;
 
 	mutex_lock(&kprobe_mutex);
 
 	/* Disable this kprobe */
-	if (__disable_kprobe(kp) == NULL)
-		ret = -EINVAL;
+	p = __disable_kprobe(kp);
+	if (IS_ERR(p))
+		ret = PTR_ERR(p);
 
 	mutex_unlock(&kprobe_mutex);
 	return ret;

@@ -2640,34 +2652,50 @@ static int arm_all_kprobes(void)
 	return ret;
 }
 
-static void disarm_all_kprobes(void)
+static int disarm_all_kprobes(void)
 {
 	struct hlist_head *head;
 	struct kprobe *p;
-	unsigned int i;
+	unsigned int i, total = 0, errors = 0;
+	int err, ret = 0;
 
 	mutex_lock(&kprobe_mutex);
 
 	/* If kprobes are already disarmed, just return */
 	if (kprobes_all_disarmed) {
 		mutex_unlock(&kprobe_mutex);
-		return;
+		return 0;
 	}
 
 	kprobes_all_disarmed = true;
-	printk(KERN_INFO "Kprobes globally disabled\n");
 
 	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 		head = &kprobe_table[i];
+		/* Disarm all kprobes on a best-effort basis */
 		hlist_for_each_entry_rcu(p, head, hlist) {
-			if (!arch_trampoline_kprobe(p) && !kprobe_disabled(p))
-				disarm_kprobe(p, false);
+			if (!arch_trampoline_kprobe(p) && !kprobe_disabled(p)) {
+				err = disarm_kprobe(p, false);
+				if (err) {
+					errors++;
+					ret = err;
+				}
+				total++;
+			}
 		}
 	}
+
+	if (errors)
+		pr_warn("Kprobes globally disabled, but failed to disarm %d out of %d probes\n",
+			errors, total);
+	else
+		pr_info("Kprobes globally disabled\n");
+
 	mutex_unlock(&kprobe_mutex);
 
 	/* Wait for disarming all kprobes by optimizer */
 	wait_for_kprobe_optimizer();
+
+	return ret;
 }
 
 /*

@@ -2710,7 +2738,7 @@ static ssize_t write_enabled_file_bool(struct file *file,
 	case 'n':
 	case 'N':
 	case '0':
-		disarm_all_kprobes();
+		ret = disarm_all_kprobes();
 		break;
 	default:
 		return -EINVAL;