diff options
Diffstat (limited to 'kernel/jump_label.c')
| -rw-r--r-- | kernel/jump_label.c | 864 |
1 files changed, 864 insertions, 0 deletions
diff --git a/kernel/jump_label.c b/kernel/jump_label.c new file mode 100644 index 000000000..4ae693ce7 --- /dev/null +++ b/kernel/jump_label.c @@ -0,0 +1,864 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * jump label support + * + * Copyright (C) 2009 Jason Baron <jbaron@redhat.com> + * Copyright (C) 2011 Peter Zijlstra + * + */ +#include <linux/memory.h> +#include <linux/uaccess.h> +#include <linux/module.h> +#include <linux/list.h> +#include <linux/slab.h> +#include <linux/sort.h> +#include <linux/err.h> +#include <linux/static_key.h> +#include <linux/jump_label_ratelimit.h> +#include <linux/bug.h> +#include <linux/cpu.h> +#include <asm/sections.h> + +/* mutex to protect coming/going of the jump_label table */ +static DEFINE_MUTEX(jump_label_mutex); + +void jump_label_lock(void) +{ + mutex_lock(&jump_label_mutex); +} + +void jump_label_unlock(void) +{ + mutex_unlock(&jump_label_mutex); +} + +static int jump_label_cmp(const void *a, const void *b) +{ + const struct jump_entry *jea = a; + const struct jump_entry *jeb = b; + + /* + * Entrires are sorted by key. + */ + if (jump_entry_key(jea) < jump_entry_key(jeb)) + return -1; + + if (jump_entry_key(jea) > jump_entry_key(jeb)) + return 1; + + /* + * In the batching mode, entries should also be sorted by the code + * inside the already sorted list of entries, enabling a bsearch in + * the vector. + */ + if (jump_entry_code(jea) < jump_entry_code(jeb)) + return -1; + + if (jump_entry_code(jea) > jump_entry_code(jeb)) + return 1; + + return 0; +} + +static void jump_label_swap(void *a, void *b, int size) +{ + long delta = (unsigned long)a - (unsigned long)b; + struct jump_entry *jea = a; + struct jump_entry *jeb = b; + struct jump_entry tmp = *jea; + + jea->code = jeb->code - delta; + jea->target = jeb->target - delta; + jea->key = jeb->key - delta; + + jeb->code = tmp.code + delta; + jeb->target = tmp.target + delta; + jeb->key = tmp.key + delta; +} + +static void +jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop) +{ + unsigned long size; + void *swapfn = NULL; + + if (IS_ENABLED(CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE)) + swapfn = jump_label_swap; + + size = (((unsigned long)stop - (unsigned long)start) + / sizeof(struct jump_entry)); + sort(start, size, sizeof(struct jump_entry), jump_label_cmp, swapfn); +} + +static void jump_label_update(struct static_key *key); + +/* + * There are similar definitions for the !CONFIG_JUMP_LABEL case in jump_label.h. + * The use of 'atomic_read()' requires atomic.h and its problematic for some + * kernel headers such as kernel.h and others. Since static_key_count() is not + * used in the branch statements as it is for the !CONFIG_JUMP_LABEL case its ok + * to have it be a function here. Similarly, for 'static_key_enable()' and + * 'static_key_disable()', which require bug.h. This should allow jump_label.h + * to be included from most/all places for CONFIG_JUMP_LABEL. + */ +int static_key_count(struct static_key *key) +{ + /* + * -1 means the first static_key_slow_inc() is in progress. + * static_key_enabled() must return true, so return 1 here. + */ + int n = atomic_read(&key->enabled); + + return n >= 0 ? n : 1; +} +EXPORT_SYMBOL_GPL(static_key_count); + +void static_key_slow_inc_cpuslocked(struct static_key *key) +{ + int v, v1; + + STATIC_KEY_CHECK_USE(key); + lockdep_assert_cpus_held(); + + /* + * Careful if we get concurrent static_key_slow_inc() 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 + * static_key_enabled(&key) for jumps to be updated properly. + * + * So give a special meaning to negative key->enabled: 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. + */ + for (v = atomic_read(&key->enabled); v > 0; v = v1) { + v1 = atomic_cmpxchg(&key->enabled, v, v + 1); + if (likely(v1 == v)) + return; + } + + jump_label_lock(); + if (atomic_read(&key->enabled) == 0) { + atomic_set(&key->enabled, -1); + jump_label_update(key); + /* + * Ensure that if the above cmpxchg loop observes our positive + * value, it must also observe all the text changes. + */ + atomic_set_release(&key->enabled, 1); + } else { + atomic_inc(&key->enabled); + } + jump_label_unlock(); +} + +void static_key_slow_inc(struct static_key *key) +{ + cpus_read_lock(); + static_key_slow_inc_cpuslocked(key); + cpus_read_unlock(); +} +EXPORT_SYMBOL_GPL(static_key_slow_inc); + +void static_key_enable_cpuslocked(struct static_key *key) +{ + STATIC_KEY_CHECK_USE(key); + lockdep_assert_cpus_held(); + + if (atomic_read(&key->enabled) > 0) { + WARN_ON_ONCE(atomic_read(&key->enabled) != 1); + return; + } + + jump_label_lock(); + if (atomic_read(&key->enabled) == 0) { + atomic_set(&key->enabled, -1); + jump_label_update(key); + /* + * See static_key_slow_inc(). + */ + atomic_set_release(&key->enabled, 1); + } + jump_label_unlock(); +} +EXPORT_SYMBOL_GPL(static_key_enable_cpuslocked); + +void static_key_enable(struct static_key *key) +{ + cpus_read_lock(); + static_key_enable_cpuslocked(key); + cpus_read_unlock(); +} +EXPORT_SYMBOL_GPL(static_key_enable); + +void static_key_disable_cpuslocked(struct static_key *key) +{ + STATIC_KEY_CHECK_USE(key); + lockdep_assert_cpus_held(); + + if (atomic_read(&key->enabled) != 1) { + WARN_ON_ONCE(atomic_read(&key->enabled) != 0); + return; + } + + jump_label_lock(); + if (atomic_cmpxchg(&key->enabled, 1, 0)) + jump_label_update(key); + jump_label_unlock(); +} +EXPORT_SYMBOL_GPL(static_key_disable_cpuslocked); + +void static_key_disable(struct static_key *key) +{ + cpus_read_lock(); + static_key_disable_cpuslocked(key); + cpus_read_unlock(); +} +EXPORT_SYMBOL_GPL(static_key_disable); + +static bool static_key_slow_try_dec(struct static_key *key) +{ + int val; + + val = atomic_fetch_add_unless(&key->enabled, -1, 1); + if (val == 1) + return false; + + /* + * 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. + */ + WARN(val < 0, "jump label: negative count!\n"); + return true; +} + +static void __static_key_slow_dec_cpuslocked(struct static_key *key) +{ + lockdep_assert_cpus_held(); + + if (static_key_slow_try_dec(key)) + 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) +{ + cpus_read_lock(); + __static_key_slow_dec_cpuslocked(key); + cpus_read_unlock(); +} + +void jump_label_update_timeout(struct work_struct *work) +{ + struct static_key_deferred *key = + container_of(work, struct static_key_deferred, work.work); + __static_key_slow_dec(&key->key); +} +EXPORT_SYMBOL_GPL(jump_label_update_timeout); + +void static_key_slow_dec(struct static_key *key) +{ + STATIC_KEY_CHECK_USE(key); + __static_key_slow_dec(key); +} +EXPORT_SYMBOL_GPL(static_key_slow_dec); + +void static_key_slow_dec_cpuslocked(struct static_key *key) +{ + STATIC_KEY_CHECK_USE(key); + __static_key_slow_dec_cpuslocked(key); +} + +void __static_key_slow_dec_deferred(struct static_key *key, + struct delayed_work *work, + unsigned long timeout) +{ + STATIC_KEY_CHECK_USE(key); + + if (static_key_slow_try_dec(key)) + return; + + schedule_delayed_work(work, timeout); +} +EXPORT_SYMBOL_GPL(__static_key_slow_dec_deferred); + +void __static_key_deferred_flush(void *key, struct delayed_work *work) +{ + STATIC_KEY_CHECK_USE(key); + flush_delayed_work(work); +} +EXPORT_SYMBOL_GPL(__static_key_deferred_flush); + +void jump_label_rate_limit(struct static_key_deferred *key, + unsigned long rl) +{ + STATIC_KEY_CHECK_USE(key); + key->timeout = rl; + INIT_DELAYED_WORK(&key->work, jump_label_update_timeout); +} +EXPORT_SYMBOL_GPL(jump_label_rate_limit); + +static int addr_conflict(struct jump_entry *entry, void *start, void *end) +{ + if (jump_entry_code(entry) <= (unsigned long)end && + jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE > (unsigned long)start) + return 1; + + return 0; +} + +static int __jump_label_text_reserved(struct jump_entry *iter_start, + struct jump_entry *iter_stop, void *start, void *end, bool init) +{ + struct jump_entry *iter; + + iter = iter_start; + while (iter < iter_stop) { + if (init || !jump_entry_is_init(iter)) { + if (addr_conflict(iter, start, end)) + return 1; + } + iter++; + } + + return 0; +} + +/* + * Update code which is definitely not currently executing. + * Architectures which need heavyweight synchronization to modify + * running code can override this to make the non-live update case + * cheaper. + */ +void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry, + enum jump_label_type type) +{ + arch_jump_label_transform(entry, type); +} + +static inline struct jump_entry *static_key_entries(struct static_key *key) +{ + WARN_ON_ONCE(key->type & JUMP_TYPE_LINKED); + return (struct jump_entry *)(key->type & ~JUMP_TYPE_MASK); +} + +static inline bool static_key_type(struct static_key *key) +{ + return key->type & JUMP_TYPE_TRUE; +} + +static inline bool static_key_linked(struct static_key *key) +{ + return key->type & JUMP_TYPE_LINKED; +} + +static inline void static_key_clear_linked(struct static_key *key) +{ + key->type &= ~JUMP_TYPE_LINKED; +} + +static inline void static_key_set_linked(struct static_key *key) +{ + key->type |= JUMP_TYPE_LINKED; +} + +/*** + * A 'struct static_key' uses a union such that it either points directly + * to a table of 'struct jump_entry' or to a linked list of modules which in + * turn point to 'struct jump_entry' tables. + * + * The two lower bits of the pointer are used to keep track of which pointer + * type is in use and to store the initial branch direction, we use an access + * function which preserves these bits. + */ +static void static_key_set_entries(struct static_key *key, + struct jump_entry *entries) +{ + unsigned long type; + + WARN_ON_ONCE((unsigned long)entries & JUMP_TYPE_MASK); + type = key->type & JUMP_TYPE_MASK; + key->entries = entries; + key->type |= type; +} + +static enum jump_label_type jump_label_type(struct jump_entry *entry) +{ + struct static_key *key = jump_entry_key(entry); + bool enabled = static_key_enabled(key); + bool branch = jump_entry_is_branch(entry); + + /* See the comment in linux/jump_label.h */ + return enabled ^ branch; +} + +static bool jump_label_can_update(struct jump_entry *entry, bool init) +{ + /* + * Cannot update code that was in an init text area. + */ + if (!init && jump_entry_is_init(entry)) + return false; + + if (!kernel_text_address(jump_entry_code(entry))) { + /* + * This skips patching built-in __exit, which + * is part of init_section_contains() but is + * not part of kernel_text_address(). + * + * Skipping built-in __exit is fine since it + * will never be executed. + */ + WARN_ONCE(!jump_entry_is_init(entry), + "can't patch jump_label at %pS", + (void *)jump_entry_code(entry)); + return false; + } + + return true; +} + +#ifndef HAVE_JUMP_LABEL_BATCH +static void __jump_label_update(struct static_key *key, + struct jump_entry *entry, + struct jump_entry *stop, + bool init) +{ + for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) { + if (jump_label_can_update(entry, init)) + arch_jump_label_transform(entry, jump_label_type(entry)); + } +} +#else +static void __jump_label_update(struct static_key *key, + struct jump_entry *entry, + struct jump_entry *stop, + bool init) +{ + for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) { + + if (!jump_label_can_update(entry, init)) + continue; + + if (!arch_jump_label_transform_queue(entry, jump_label_type(entry))) { + /* + * Queue is full: Apply the current queue and try again. + */ + arch_jump_label_transform_apply(); + BUG_ON(!arch_jump_label_transform_queue(entry, jump_label_type(entry))); + } + } + arch_jump_label_transform_apply(); +} +#endif + +void __init jump_label_init(void) +{ + struct jump_entry *iter_start = __start___jump_table; + struct jump_entry *iter_stop = __stop___jump_table; + struct static_key *key = NULL; + struct jump_entry *iter; + + /* + * Since we are initializing the static_key.enabled field with + * with the 'raw' int values (to avoid pulling in atomic.h) in + * jump_label.h, let's make sure that is safe. There are only two + * cases to check since we initialize to 0 or 1. + */ + BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0); + BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1); + + if (static_key_initialized) + return; + + cpus_read_lock(); + jump_label_lock(); + jump_label_sort_entries(iter_start, iter_stop); + + for (iter = iter_start; iter < iter_stop; iter++) { + struct static_key *iterk; + + /* rewrite NOPs */ + 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; + + key = iterk; + static_key_set_entries(key, iter); + } + static_key_initialized = true; + jump_label_unlock(); + cpus_read_unlock(); +} + +#ifdef CONFIG_MODULES + +static enum jump_label_type jump_label_init_type(struct jump_entry *entry) +{ + struct static_key *key = jump_entry_key(entry); + bool type = static_key_type(key); + bool branch = jump_entry_is_branch(entry); + + /* See the comment in linux/jump_label.h */ + return type ^ branch; +} + +struct static_key_mod { + struct static_key_mod *next; + struct jump_entry *entries; + struct module *mod; +}; + +static inline struct static_key_mod *static_key_mod(struct static_key *key) +{ + WARN_ON_ONCE(!static_key_linked(key)); + return (struct static_key_mod *)(key->type & ~JUMP_TYPE_MASK); +} + +/*** + * key->type and key->next are the same via union. + * This sets key->next and preserves the type bits. + * + * See additional comments above static_key_set_entries(). + */ +static void static_key_set_mod(struct static_key *key, + struct static_key_mod *mod) +{ + unsigned long type; + + WARN_ON_ONCE((unsigned long)mod & JUMP_TYPE_MASK); + type = key->type & JUMP_TYPE_MASK; + key->next = mod; + key->type |= type; +} + +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(); + + if (!mod) + return 0; + + ret = __jump_label_text_reserved(mod->jump_entries, + mod->jump_entries + mod->num_jump_entries, + start, end, mod->state == MODULE_STATE_COMING); + + module_put(mod); + + return ret; +} + +static void __jump_label_mod_update(struct static_key *key) +{ + struct static_key_mod *mod; + + for (mod = static_key_mod(key); mod; mod = mod->next) { + struct jump_entry *stop; + struct module *m; + + /* + * NULL if the static_key is defined in a module + * that does not use it + */ + if (!mod->entries) + continue; + + m = mod->mod; + if (!m) + stop = __stop___jump_table; + else + stop = m->jump_entries + m->num_jump_entries; + __jump_label_update(key, mod->entries, stop, + m && m->state == MODULE_STATE_COMING); + } +} + +/*** + * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop() + * @mod: module to patch + * + * Allow for run-time selection of the optimal nops. Before the module + * loads patch these with arch_get_jump_label_nop(), which is specified by + * the arch specific jump label code. + */ +void jump_label_apply_nops(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; + + /* if the module doesn't have jump label entries, just return */ + if (iter_start == iter_stop) + return; + + for (iter = iter_start; iter < iter_stop; iter++) { + /* Only write NOPs for arch_branch_static(). */ + if (jump_label_init_type(iter) == JUMP_LABEL_NOP) + arch_jump_label_transform_static(iter, JUMP_LABEL_NOP); + } +} + +static int jump_label_add_module(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; + struct static_key *key = NULL; + struct static_key_mod *jlm, *jlm2; + + /* if the module doesn't have jump label entries, just return */ + if (iter_start == iter_stop) + return 0; + + jump_label_sort_entries(iter_start, iter_stop); + + 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; + + key = iterk; + if (within_module((unsigned long)key, mod)) { + static_key_set_entries(key, iter); + continue; + } + jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL); + if (!jlm) + return -ENOMEM; + if (!static_key_linked(key)) { + jlm2 = kzalloc(sizeof(struct static_key_mod), + GFP_KERNEL); + if (!jlm2) { + kfree(jlm); + return -ENOMEM; + } + preempt_disable(); + jlm2->mod = __module_address((unsigned long)key); + preempt_enable(); + jlm2->entries = static_key_entries(key); + jlm2->next = NULL; + static_key_set_mod(key, jlm2); + static_key_set_linked(key); + } + jlm->mod = mod; + jlm->entries = iter; + jlm->next = static_key_mod(key); + static_key_set_mod(key, jlm); + static_key_set_linked(key); + + /* 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, true); + } + + return 0; +} + +static void jump_label_del_module(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; + struct static_key *key = NULL; + struct static_key_mod *jlm, **prev; + + for (iter = iter_start; iter < iter_stop; iter++) { + if (jump_entry_key(iter) == key) + continue; + + key = jump_entry_key(iter); + + if (within_module((unsigned long)key, mod)) + continue; + + /* No memory during module load */ + if (WARN_ON(!static_key_linked(key))) + continue; + + prev = &key->next; + jlm = static_key_mod(key); + + while (jlm && jlm->mod != mod) { + prev = &jlm->next; + jlm = jlm->next; + } + + /* No memory during module load */ + if (WARN_ON(!jlm)) + continue; + + if (prev == &key->next) + static_key_set_mod(key, jlm->next); + else + *prev = jlm->next; + + kfree(jlm); + + jlm = static_key_mod(key); + /* if only one etry is left, fold it back into the static_key */ + if (jlm->next == NULL) { + static_key_set_entries(key, jlm->entries); + static_key_clear_linked(key); + kfree(jlm); + } + } +} + +static int +jump_label_module_notify(struct notifier_block *self, unsigned long val, + void *data) +{ + struct module *mod = data; + int ret = 0; + + cpus_read_lock(); + jump_label_lock(); + + switch (val) { + case MODULE_STATE_COMING: + ret = jump_label_add_module(mod); + if (ret) { + WARN(1, "Failed to allocate memory: jump_label may not work properly.\n"); + jump_label_del_module(mod); + } + break; + case MODULE_STATE_GOING: + jump_label_del_module(mod); + break; + } + + jump_label_unlock(); + cpus_read_unlock(); + + return notifier_from_errno(ret); +} + +static struct notifier_block jump_label_module_nb = { + .notifier_call = jump_label_module_notify, + .priority = 1, /* higher than tracepoints */ +}; + +static __init int jump_label_init_module(void) +{ + return register_module_notifier(&jump_label_module_nb); +} +early_initcall(jump_label_init_module); + +#endif /* CONFIG_MODULES */ + +/*** + * jump_label_text_reserved - check if addr range is reserved + * @start: start text addr + * @end: end text addr + * + * checks if the text addr located between @start and @end + * overlaps with any of the jump label patch addresses. Code + * that wants to modify kernel text should first verify that + * it does not overlap with any of the jump label addresses. + * Caller must hold jump_label_mutex. + * + * returns 1 if there is an overlap, 0 otherwise + */ +int jump_label_text_reserved(void *start, void *end) +{ + bool init = system_state < SYSTEM_RUNNING; + int ret = __jump_label_text_reserved(__start___jump_table, + __stop___jump_table, start, end, init); + + if (ret) + return ret; + +#ifdef CONFIG_MODULES + ret = __jump_label_mod_text_reserved(start, end); +#endif + return ret; +} + +static void jump_label_update(struct static_key *key) +{ + struct jump_entry *stop = __stop___jump_table; + struct jump_entry *entry; +#ifdef CONFIG_MODULES + struct module *mod; + + if (static_key_linked(key)) { + __jump_label_mod_update(key); + return; + } + + preempt_disable(); + mod = __module_address((unsigned long)key); + if (mod) + stop = mod->jump_entries + mod->num_jump_entries; + preempt_enable(); +#endif + entry = static_key_entries(key); + /* if there are no users, entry can be NULL */ + if (entry) + __jump_label_update(key, entry, stop, + system_state < SYSTEM_RUNNING); +} + +#ifdef CONFIG_STATIC_KEYS_SELFTEST +static DEFINE_STATIC_KEY_TRUE(sk_true); +static DEFINE_STATIC_KEY_FALSE(sk_false); + +static __init int jump_label_test(void) +{ + int i; + + for (i = 0; i < 2; i++) { + WARN_ON(static_key_enabled(&sk_true.key) != true); + WARN_ON(static_key_enabled(&sk_false.key) != false); + + WARN_ON(!static_branch_likely(&sk_true)); + WARN_ON(!static_branch_unlikely(&sk_true)); + WARN_ON(static_branch_likely(&sk_false)); + WARN_ON(static_branch_unlikely(&sk_false)); + + static_branch_disable(&sk_true); + static_branch_enable(&sk_false); + + WARN_ON(static_key_enabled(&sk_true.key) == true); + WARN_ON(static_key_enabled(&sk_false.key) == false); + + WARN_ON(static_branch_likely(&sk_true)); + WARN_ON(static_branch_unlikely(&sk_true)); + WARN_ON(!static_branch_likely(&sk_false)); + WARN_ON(!static_branch_unlikely(&sk_false)); + + static_branch_enable(&sk_true); + static_branch_disable(&sk_false); + } + + return 0; +} +early_initcall(jump_label_test); +#endif /* STATIC_KEYS_SELFTEST */ |