1 files changed, 137 insertions, 47 deletions

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index d9c822bbffb8..7cb19e601426 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -131,13 +131,16 @@ bool static_key_fast_inc_not_disabled(struct static_key *key)
 	STATIC_KEY_CHECK_USE(key);
 	/*
 	 * Negative key->enabled has a special meaning: it sends
-	 * static_key_slow_inc() down the slow path, and it is non-zero
-	 * so it counts as "enabled" in jump_label_update().  Note that
-	 * atomic_inc_unless_negative() checks >= 0, so roll our own.
+	 * static_key_slow_inc/dec() down the slow path, and it is non-zero
+	 * so it counts as "enabled" in jump_label_update().
+	 *
+	 * The INT_MAX overflow condition is either used by the networking
+	 * code to reset or detected in the slow path of
+	 * static_key_slow_inc_cpuslocked().
 	 */
 	v = atomic_read(&key->enabled);
 	do {
-		if (v <= 0 || (v + 1) < 0)
+		if (v <= 0 || v == INT_MAX)
 			return false;
 	} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
 
@@ -150,7 +153,7 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
 	lockdep_assert_cpus_held();
 
 	/*
-	 * Careful if we get concurrent static_key_slow_inc() calls;
+	 * Careful if we get concurrent static_key_slow_inc/dec() calls;
 	 * later calls must wait for the first one to _finish_ the
 	 * jump_label_update() process.  At the same time, however,
 	 * the jump_label_update() call below wants to see
@@ -159,22 +162,24 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
 	if (static_key_fast_inc_not_disabled(key))
 		return true;
 
-	jump_label_lock();
-	if (atomic_read(&key->enabled) == 0) {
-		atomic_set(&key->enabled, -1);
+	guard(mutex)(&jump_label_mutex);
+	/* Try to mark it as 'enabling in progress. */
+	if (!atomic_cmpxchg(&key->enabled, 0, -1)) {
 		jump_label_update(key);
 		/*
-		 * Ensure that if the above cmpxchg loop observes our positive
-		 * value, it must also observe all the text changes.
+		 * Ensure that when static_key_fast_inc_not_disabled() or
+		 * static_key_dec_not_one() observe the positive value,
+		 * they must also observe all the text changes.
 		 */
 		atomic_set_release(&key->enabled, 1);
 	} else {
-		if (WARN_ON_ONCE(!static_key_fast_inc_not_disabled(key))) {
-			jump_label_unlock();
+		/*
+		 * While holding the mutex this should never observe
+		 * anything else than a value >= 1 and succeed
+		 */
+		if (WARN_ON_ONCE(!static_key_fast_inc_not_disabled(key)))
 			return false;
-		}
 	}
-	jump_label_unlock();
 	return true;
 }
 
@@ -231,7 +236,7 @@ void static_key_disable_cpuslocked(struct static_key *key)
 	}
 
 	jump_label_lock();
-	if (atomic_cmpxchg(&key->enabled, 1, 0))
+	if (atomic_cmpxchg(&key->enabled, 1, 0) == 1)
 		jump_label_update(key);
 	jump_label_unlock();
 }
@@ -245,36 +250,69 @@ void static_key_disable(struct static_key *key)
 }
 EXPORT_SYMBOL_GPL(static_key_disable);
 
-static bool static_key_slow_try_dec(struct static_key *key)
+static bool static_key_dec_not_one(struct static_key *key)
 {
-	int val;
-
-	val = atomic_fetch_add_unless(&key->enabled, -1, 1);
-	if (val == 1)
-		return false;
+	int v;
 
 	/*
-	 * The negative count check is valid even when a negative
-	 * key->enabled is in use by static_key_slow_inc(); a
-	 * __static_key_slow_dec() before the first static_key_slow_inc()
-	 * returns is unbalanced, because all other static_key_slow_inc()
-	 * instances block while the update is in progress.
+	 * Go into the slow path if key::enabled is less than or equal than
+	 * one. One is valid to shut down the key, anything less than one
+	 * is an imbalance, which is handled at the call site.
+	 *
+	 * That includes the special case of '-1' which is set in
+	 * static_key_slow_inc_cpuslocked(), but that's harmless as it is
+	 * fully serialized in the slow path below. By the time this task
+	 * acquires the jump label lock the value is back to one and the
+	 * retry under the lock must succeed.
 	 */
-	WARN(val < 0, "jump label: negative count!\n");
+	v = atomic_read(&key->enabled);
+	do {
+		/*
+		 * Warn about the '-1' case though; since that means a
+		 * decrement is concurrent with a first (0->1) increment. IOW
+		 * people are trying to disable something that wasn't yet fully
+		 * enabled. This suggests an ordering problem on the user side.
+		 */
+		WARN_ON_ONCE(v < 0);
+
+		/*
+		 * Warn about underflow, and lie about success in an attempt to
+		 * not make things worse.
+		 */
+		if (WARN_ON_ONCE(v == 0))
+			return true;
+
+		if (v <= 1)
+			return false;
+	} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v - 1)));
+
 	return true;
 }
 
 static void __static_key_slow_dec_cpuslocked(struct static_key *key)
 {
 	lockdep_assert_cpus_held();
+	int val;
 
-	if (static_key_slow_try_dec(key))
+	if (static_key_dec_not_one(key))
+		return;
+
+	guard(mutex)(&jump_label_mutex);
+	val = atomic_read(&key->enabled);
+	/*
+	 * It should be impossible to observe -1 with jump_label_mutex held,
+	 * see static_key_slow_inc_cpuslocked().
+	 */
+	if (WARN_ON_ONCE(val == -1))
+		return;
+	/*
+	 * Cannot already be 0, something went sideways.
+	 */
+	if (WARN_ON_ONCE(val == 0))
 		return;
 
-	jump_label_lock();
 	if (atomic_dec_and_test(&key->enabled))
 		jump_label_update(key);
-	jump_label_unlock();
 }
 
 static void __static_key_slow_dec(struct static_key *key)
@@ -311,7 +349,7 @@ void __static_key_slow_dec_deferred(struct static_key *key,
 {
 	STATIC_KEY_CHECK_USE(key);
 
-	if (static_key_slow_try_dec(key))
+	if (static_key_dec_not_one(key))
 		return;
 
 	schedule_delayed_work(work, timeout);
@@ -530,6 +568,45 @@ void __init jump_label_init(void)
 	cpus_read_unlock();
 }
 
+static inline bool static_key_sealed(struct static_key *key)
+{
+	return (key->type & JUMP_TYPE_LINKED) && !(key->type & ~JUMP_TYPE_MASK);
+}
+
+static inline void static_key_seal(struct static_key *key)
+{
+	unsigned long type = key->type & JUMP_TYPE_TRUE;
+	key->type = JUMP_TYPE_LINKED | type;
+}
+
+void jump_label_init_ro(void)
+{
+	struct jump_entry *iter_start = __start___jump_table;
+	struct jump_entry *iter_stop = __stop___jump_table;
+	struct jump_entry *iter;
+
+	if (WARN_ON_ONCE(!static_key_initialized))
+		return;
+
+	cpus_read_lock();
+	jump_label_lock();
+
+	for (iter = iter_start; iter < iter_stop; iter++) {
+		struct static_key *iterk = jump_entry_key(iter);
+
+		if (!is_kernel_ro_after_init((unsigned long)iterk))
+			continue;
+
+		if (static_key_sealed(iterk))
+			continue;
+
+		static_key_seal(iterk);
+	}
+
+	jump_label_unlock();
+	cpus_read_unlock();
+}
+
 #ifdef CONFIG_MODULES
 
 enum jump_label_type jump_label_init_type(struct jump_entry *entry)
@@ -576,13 +653,12 @@ static int __jump_label_mod_text_reserved(void *start, void *end)
 	struct module *mod;
 	int ret;
 
-	preempt_disable();
-	mod = __module_text_address((unsigned long)start);
-	WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
-	if (!try_module_get(mod))
-		mod = NULL;
-	preempt_enable();
-
+	scoped_guard(rcu) {
+		mod = __module_text_address((unsigned long)start);
+		WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
+		if (!try_module_get(mod))
+			mod = NULL;
+	}
 	if (!mod)
 		return 0;
 
@@ -650,6 +726,15 @@ static int jump_label_add_module(struct module *mod)
 			static_key_set_entries(key, iter);
 			continue;
 		}
+
+		/*
+		 * If the key was sealed at init, then there's no need to keep a
+		 * reference to its module entries - just patch them now and be
+		 * done with it.
+		 */
+		if (static_key_sealed(key))
+			goto do_poke;
+
 		jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 		if (!jlm)
 			return -ENOMEM;
@@ -660,9 +745,9 @@ static int jump_label_add_module(struct module *mod)
 				kfree(jlm);
 				return -ENOMEM;
 			}
-			preempt_disable();
-			jlm2->mod = __module_address((unsigned long)key);
-			preempt_enable();
+			scoped_guard(rcu)
+				jlm2->mod = __module_address((unsigned long)key);
+
 			jlm2->entries = static_key_entries(key);
 			jlm2->next = NULL;
 			static_key_set_mod(key, jlm2);
@@ -675,6 +760,7 @@ static int jump_label_add_module(struct module *mod)
 		static_key_set_linked(key);
 
 		/* Only update if we've changed from our initial state */
+do_poke:
 		if (jump_label_type(iter) != jump_label_init_type(iter))
 			__jump_label_update(key, iter, iter_stop, true);
 	}
@@ -699,6 +785,10 @@ static void jump_label_del_module(struct module *mod)
 		if (within_module((unsigned long)key, mod))
 			continue;
 
+		/* No @jlm allocated because key was sealed at init. */
+		if (static_key_sealed(key))
+			continue;
+
 		/* No memory during module load */
 		if (WARN_ON(!static_key_linked(key)))
 			continue;
@@ -815,13 +905,13 @@ static void jump_label_update(struct static_key *key)
 		return;
 	}
 
-	preempt_disable();
-	mod = __module_address((unsigned long)key);
-	if (mod) {
-		stop = mod->jump_entries + mod->num_jump_entries;
-		init = mod->state == MODULE_STATE_COMING;
+	scoped_guard(rcu) {
+		mod = __module_address((unsigned long)key);
+		if (mod) {
+			stop = mod->jump_entries + mod->num_jump_entries;
+			init = mod->state == MODULE_STATE_COMING;
+		}
 	}
-	preempt_enable();
 #endif
 	entry = static_key_entries(key);
 	/* if there are no users, entry can be NULL */