jump_label,module: Don't alloc static_key_mod for __ro_after_init keys

When a static_key is marked ro_after_init, its state will never change
(after init), therefore jump_label_update() will never need to iterate
the entries, and thus module load won't actually need to track this --
avoiding the static_key::next write.

Therefore, mark these keys such that jump_label_add_module() might
recognise them and avoid the modification.

Use the special state: 'static_key_linked(key) && !static_key_mod(key)'
to denote such keys.

jump_label_add_module() does not exist under CONFIG_JUMP_LABEL=n, so the
newly-introduced jump_label_init_ro() can be defined as a nop for that
configuration.

[ mingo: Renamed jump_label_ro() to jump_label_init_ro() ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20240313180106.2917308-2-vschneid@redhat.com

diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index db13bb620f527e2a0d8204cfdafe877975c35394..c768de6f19a9a90d04eab66f522bad2f10ef1fd9 100644 (file)
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -180,6 +180,11 @@ static inline bool is_kernel_rodata(unsigned long addr)
               addr < (unsigned long)__end_rodata;
 }
 
+static inline bool is_kernel_ro_after_init(unsigned long addr)
+{
+       return addr >= (unsigned long)__start_ro_after_init &&
+              addr < (unsigned long)__end_ro_after_init;
+}
 /**
  * is_kernel_inittext - checks if the pointer address is located in the
  *                      .init.text section

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index f0a949b7c9733ce3209fb3adc561ac2f4d93d3ca..f5a2727ca4a9a9a8d675656632cfad4ff045c231 100644 (file)
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -216,6 +216,7 @@ extern struct jump_entry __start___jump_table[];
 extern struct jump_entry __stop___jump_table[];
 
 extern void jump_label_init(void);
+extern void jump_label_init_ro(void);
 extern void jump_label_lock(void);
 extern void jump_label_unlock(void);
 extern void arch_jump_label_transform(struct jump_entry *entry,
@@ -265,6 +266,8 @@ static __always_inline void jump_label_init(void)
        static_key_initialized = true;
 }
 
+static __always_inline void jump_label_init_ro(void) { }
+
 static __always_inline bool static_key_false(struct static_key *key)
 {
        if (unlikely_notrace(static_key_count(key) > 0))

diff --git a/init/main.c b/init/main.c
index 2ca52474d0c3032e44ae410add7b2430218f9c41..6c3f251d6ef8ad7f80e13fa8fa27e50736058fe0 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -1408,6 +1408,7 @@ static void mark_readonly(void)
                 * insecure pages which are W+X.
                 */
                flush_module_init_free_work();
+               jump_label_init_ro();
                mark_rodata_ro();
                debug_checkwx();
                rodata_test();

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index d9c822bbffb8d3c8977d410e683bb8a7c578f3c4..3218fa5688b9394097f9c0bdcddb3683641178ba 100644 (file)
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -530,6 +530,45 @@ 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)
@@ -650,6 +689,15 @@ 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;
@@ -675,6 +723,7 @@ 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 +748,10 @@ 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;