jump_label: Annotate entries that operate on __init code earlier

Jump table entries are mostly read-only, with the exception of the
init and module loader code that defuses entries that point into init
code when the code being referred to is freed.

For robustness, it would be better to move these entries into the
ro_after_init section, but clearing the 'code' member of each jump
table entry referring to init code at module load time races with the
module_enable_ro() call that remaps the ro_after_init section read
only, so we'd like to do it earlier.

So given that whether such an entry refers to init code can be decided
much earlier, we can pull this check forward. Since we may still need
the code entry at this point, let's switch to setting a low bit in the
'key' member just like we do to annotate the default state of a jump
table entry.

Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Arnd Bergmann <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Jessica Yu <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

include/linux/jump_label.h

···
 
 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
 {
-	long offset = entry->key & ~1L;
+	long offset = entry->key & ~3L;
 
 	return (struct static_key *)((unsigned long)&entry->key + offset);
 }
···
 
 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
 {
-	return (struct static_key *)((unsigned long)entry->key & ~1UL);
+	return (struct static_key *)((unsigned long)entry->key & ~3UL);
 }
 
 #endif
···
 
 static inline bool jump_entry_is_init(const struct jump_entry *entry)
 {
-	return entry->code == 0;
+	return (unsigned long)entry->key & 2UL;
 }
 
 static inline void jump_entry_set_init(struct jump_entry *entry)
 {
-	entry->code = 0;
+	entry->key |= 2;
 }
 
 #endif
···
 extern struct jump_entry __stop___jump_table[];
 
 extern void jump_label_init(void);
-extern void jump_label_invalidate_initmem(void);
 extern void jump_label_lock(void);
 extern void jump_label_unlock(void);
 extern void arch_jump_label_transform(struct jump_entry *entry,
···
 {
 	static_key_initialized = true;
 }
-
-static inline void jump_label_invalidate_initmem(void) {}
 
 static __always_inline bool static_key_false(struct static_key *key)
 {

init/main.c

···
 	/* need to finish all async __init code before freeing the memory */
 	async_synchronize_full();
 	ftrace_free_init_mem();
-	jump_label_invalidate_initmem();
 	free_initmem();
 	mark_readonly();
 

kernel/jump_label.c

···
 
 static void __jump_label_update(struct static_key *key,
 				struct jump_entry *entry,
-				struct jump_entry *stop)
+				struct jump_entry *stop,
+				bool init)
 {
 	for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
 		/*
 		 * An entry->code of 0 indicates an entry which has been
 		 * disabled because it was in an init text area.
 		 */
-		if (!jump_entry_is_init(entry)) {
+		if (init || !jump_entry_is_init(entry)) {
 			if (kernel_text_address(jump_entry_code(entry)))
 				arch_jump_label_transform(entry, jump_label_type(entry));
 			else
···
 		if (jump_label_type(iter) == JUMP_LABEL_NOP)
 			arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 
+		if (init_section_contains((void *)jump_entry_code(iter), 1))
+			jump_entry_set_init(iter);
+
 		iterk = jump_entry_key(iter);
 		if (iterk == key)
 			continue;
···
 	static_key_initialized = true;
 	jump_label_unlock();
 	cpus_read_unlock();
-}
-
-/* Disable any jump label entries in __init/__exit code */
-void __init jump_label_invalidate_initmem(void)
-{
-	struct jump_entry *iter_start = __start___jump_table;
-	struct jump_entry *iter_stop = __stop___jump_table;
-	struct jump_entry *iter;
-
-	for (iter = iter_start; iter < iter_stop; iter++) {
-		if (init_section_contains((void *)jump_entry_code(iter), 1))
-			jump_entry_set_init(iter);
-	}
 }
 
 #ifdef CONFIG_MODULES
···
 			stop = __stop___jump_table;
 		else
 			stop = m->jump_entries + m->num_jump_entries;
-		__jump_label_update(key, mod->entries, stop);
+		__jump_label_update(key, mod->entries, stop,
+				    m->state == MODULE_STATE_COMING);
 	}
 }
 
···
 	for (iter = iter_start; iter < iter_stop; iter++) {
 		struct static_key *iterk;
 
+		if (within_module_init(jump_entry_code(iter), mod))
+			jump_entry_set_init(iter);
+
 		iterk = jump_entry_key(iter);
 		if (iterk == key)
 			continue;
···
 
 		/* Only update if we've changed from our initial state */
 		if (jump_label_type(iter) != jump_label_init_type(iter))
-			__jump_label_update(key, iter, iter_stop);
+			__jump_label_update(key, iter, iter_stop, true);
 	}
 
 	return 0;
···
 	}
 }
 
-/* Disable any jump label entries in module init code */
-static void jump_label_invalidate_module_init(struct module *mod)
-{
-	struct jump_entry *iter_start = mod->jump_entries;
-	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
-	struct jump_entry *iter;
-
-	for (iter = iter_start; iter < iter_stop; iter++) {
-		if (within_module_init(jump_entry_code(iter), mod))
-			jump_entry_set_init(iter);
-	}
-}
-
 static int
 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 			 void *data)
···
 		break;
 	case MODULE_STATE_GOING:
 		jump_label_del_module(mod);
-		break;
-	case MODULE_STATE_LIVE:
-		jump_label_invalidate_module_init(mod);
 		break;
 	}
 
···
 	entry = static_key_entries(key);
 	/* if there are no users, entry can be NULL */
 	if (entry)
-		__jump_label_update(key, entry, stop);
+		__jump_label_update(key, entry, stop,
+				    system_state < SYSTEM_RUNNING);
 }
 
 #ifdef CONFIG_STATIC_KEYS_SELFTEST