From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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_ro() can be defined as a nop for that configuration. Link: http://lore.kernel.org/r/20230705204142.GB2813335@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> [Added comments and build fix] Signed-off-by: Valentin Schneider <vschneid@xxxxxxxxxx> Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> --- include/asm-generic/sections.h | 5 ++++ include/linux/jump_label.h | 3 ++ init/main.c | 1 + kernel/jump_label.c | 53 ++++++++++++++++++++++++++++++++++ 4 files changed, 62 insertions(+) diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h index db13bb620f527..c768de6f19a9a 100644 --- 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 f0a949b7c9733..3b103d88c139e 100644 --- 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_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_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 7dce08198b133..6fc421b4d5fdb 100644 --- a/init/main.c +++ b/init/main.c @@ -1412,6 +1412,7 @@ static void mark_readonly(void) * insecure pages which are W+X. */ rcu_barrier(); + jump_label_ro(); mark_rodata_ro(); rodata_test(); } else diff --git a/kernel/jump_label.c b/kernel/jump_label.c index d9c822bbffb8d..7e3e8d1a0fea7 100644 --- 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_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; -- 2.43.0
