Root/kernel/jump_label.c

1/*
2 * jump label support
3 *
4 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
5 * Copyright (C) 2011 Peter Zijlstra <pzijlstr@redhat.com>
6 *
7 */
8#include <linux/memory.h>
9#include <linux/uaccess.h>
10#include <linux/module.h>
11#include <linux/list.h>
12#include <linux/slab.h>
13#include <linux/sort.h>
14#include <linux/err.h>
15#include <linux/static_key.h>
16
17#ifdef HAVE_JUMP_LABEL
18
19/* mutex to protect coming/going of the the jump_label table */
20static DEFINE_MUTEX(jump_label_mutex);
21
22void jump_label_lock(void)
23{
24    mutex_lock(&jump_label_mutex);
25}
26
27void jump_label_unlock(void)
28{
29    mutex_unlock(&jump_label_mutex);
30}
31
32static int jump_label_cmp(const void *a, const void *b)
33{
34    const struct jump_entry *jea = a;
35    const struct jump_entry *jeb = b;
36
37    if (jea->key < jeb->key)
38        return -1;
39
40    if (jea->key > jeb->key)
41        return 1;
42
43    return 0;
44}
45
46static void
47jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
48{
49    unsigned long size;
50
51    size = (((unsigned long)stop - (unsigned long)start)
52                    / sizeof(struct jump_entry));
53    sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
54}
55
56static void jump_label_update(struct static_key *key, int enable);
57
58void static_key_slow_inc(struct static_key *key)
59{
60    if (atomic_inc_not_zero(&key->enabled))
61        return;
62
63    jump_label_lock();
64    if (atomic_read(&key->enabled) == 0) {
65        if (!jump_label_get_branch_default(key))
66            jump_label_update(key, JUMP_LABEL_ENABLE);
67        else
68            jump_label_update(key, JUMP_LABEL_DISABLE);
69    }
70    atomic_inc(&key->enabled);
71    jump_label_unlock();
72}
73EXPORT_SYMBOL_GPL(static_key_slow_inc);
74
75static void __static_key_slow_dec(struct static_key *key,
76        unsigned long rate_limit, struct delayed_work *work)
77{
78    if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
79        WARN(atomic_read(&key->enabled) < 0,
80             "jump label: negative count!\n");
81        return;
82    }
83
84    if (rate_limit) {
85        atomic_inc(&key->enabled);
86        schedule_delayed_work(work, rate_limit);
87    } else {
88        if (!jump_label_get_branch_default(key))
89            jump_label_update(key, JUMP_LABEL_DISABLE);
90        else
91            jump_label_update(key, JUMP_LABEL_ENABLE);
92    }
93    jump_label_unlock();
94}
95
96static void jump_label_update_timeout(struct work_struct *work)
97{
98    struct static_key_deferred *key =
99        container_of(work, struct static_key_deferred, work.work);
100    __static_key_slow_dec(&key->key, 0, NULL);
101}
102
103void static_key_slow_dec(struct static_key *key)
104{
105    __static_key_slow_dec(key, 0, NULL);
106}
107EXPORT_SYMBOL_GPL(static_key_slow_dec);
108
109void static_key_slow_dec_deferred(struct static_key_deferred *key)
110{
111    __static_key_slow_dec(&key->key, key->timeout, &key->work);
112}
113EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
114
115void jump_label_rate_limit(struct static_key_deferred *key,
116        unsigned long rl)
117{
118    key->timeout = rl;
119    INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
120}
121
122static int addr_conflict(struct jump_entry *entry, void *start, void *end)
123{
124    if (entry->code <= (unsigned long)end &&
125        entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
126        return 1;
127
128    return 0;
129}
130
131static int __jump_label_text_reserved(struct jump_entry *iter_start,
132        struct jump_entry *iter_stop, void *start, void *end)
133{
134    struct jump_entry *iter;
135
136    iter = iter_start;
137    while (iter < iter_stop) {
138        if (addr_conflict(iter, start, end))
139            return 1;
140        iter++;
141    }
142
143    return 0;
144}
145
146/*
147 * Update code which is definitely not currently executing.
148 * Architectures which need heavyweight synchronization to modify
149 * running code can override this to make the non-live update case
150 * cheaper.
151 */
152void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
153                        enum jump_label_type type)
154{
155    arch_jump_label_transform(entry, type);
156}
157
158static void __jump_label_update(struct static_key *key,
159                struct jump_entry *entry,
160                struct jump_entry *stop, int enable)
161{
162    for (; (entry < stop) &&
163          (entry->key == (jump_label_t)(unsigned long)key);
164          entry++) {
165        /*
166         * entry->code set to 0 invalidates module init text sections
167         * kernel_text_address() verifies we are not in core kernel
168         * init code, see jump_label_invalidate_module_init().
169         */
170        if (entry->code && kernel_text_address(entry->code))
171            arch_jump_label_transform(entry, enable);
172    }
173}
174
175static enum jump_label_type jump_label_type(struct static_key *key)
176{
177    bool true_branch = jump_label_get_branch_default(key);
178    bool state = static_key_enabled(key);
179
180    if ((!true_branch && state) || (true_branch && !state))
181        return JUMP_LABEL_ENABLE;
182
183    return JUMP_LABEL_DISABLE;
184}
185
186void __init jump_label_init(void)
187{
188    struct jump_entry *iter_start = __start___jump_table;
189    struct jump_entry *iter_stop = __stop___jump_table;
190    struct static_key *key = NULL;
191    struct jump_entry *iter;
192
193    jump_label_lock();
194    jump_label_sort_entries(iter_start, iter_stop);
195
196    for (iter = iter_start; iter < iter_stop; iter++) {
197        struct static_key *iterk;
198
199        iterk = (struct static_key *)(unsigned long)iter->key;
200        arch_jump_label_transform_static(iter, jump_label_type(iterk));
201        if (iterk == key)
202            continue;
203
204        key = iterk;
205        /*
206         * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
207         */
208        *((unsigned long *)&key->entries) += (unsigned long)iter;
209#ifdef CONFIG_MODULES
210        key->next = NULL;
211#endif
212    }
213    jump_label_unlock();
214}
215
216#ifdef CONFIG_MODULES
217
218struct static_key_mod {
219    struct static_key_mod *next;
220    struct jump_entry *entries;
221    struct module *mod;
222};
223
224static int __jump_label_mod_text_reserved(void *start, void *end)
225{
226    struct module *mod;
227
228    mod = __module_text_address((unsigned long)start);
229    if (!mod)
230        return 0;
231
232    WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
233
234    return __jump_label_text_reserved(mod->jump_entries,
235                mod->jump_entries + mod->num_jump_entries,
236                start, end);
237}
238
239static void __jump_label_mod_update(struct static_key *key, int enable)
240{
241    struct static_key_mod *mod = key->next;
242
243    while (mod) {
244        struct module *m = mod->mod;
245
246        __jump_label_update(key, mod->entries,
247                    m->jump_entries + m->num_jump_entries,
248                    enable);
249        mod = mod->next;
250    }
251}
252
253/***
254 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
255 * @mod: module to patch
256 *
257 * Allow for run-time selection of the optimal nops. Before the module
258 * loads patch these with arch_get_jump_label_nop(), which is specified by
259 * the arch specific jump label code.
260 */
261void jump_label_apply_nops(struct module *mod)
262{
263    struct jump_entry *iter_start = mod->jump_entries;
264    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
265    struct jump_entry *iter;
266
267    /* if the module doesn't have jump label entries, just return */
268    if (iter_start == iter_stop)
269        return;
270
271    for (iter = iter_start; iter < iter_stop; iter++) {
272        arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
273    }
274}
275
276static int jump_label_add_module(struct module *mod)
277{
278    struct jump_entry *iter_start = mod->jump_entries;
279    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
280    struct jump_entry *iter;
281    struct static_key *key = NULL;
282    struct static_key_mod *jlm;
283
284    /* if the module doesn't have jump label entries, just return */
285    if (iter_start == iter_stop)
286        return 0;
287
288    jump_label_sort_entries(iter_start, iter_stop);
289
290    for (iter = iter_start; iter < iter_stop; iter++) {
291        struct static_key *iterk;
292
293        iterk = (struct static_key *)(unsigned long)iter->key;
294        if (iterk == key)
295            continue;
296
297        key = iterk;
298        if (__module_address(iter->key) == mod) {
299            /*
300             * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
301             */
302            *((unsigned long *)&key->entries) += (unsigned long)iter;
303            key->next = NULL;
304            continue;
305        }
306        jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
307        if (!jlm)
308            return -ENOMEM;
309        jlm->mod = mod;
310        jlm->entries = iter;
311        jlm->next = key->next;
312        key->next = jlm;
313
314        if (jump_label_type(key) == JUMP_LABEL_ENABLE)
315            __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
316    }
317
318    return 0;
319}
320
321static void jump_label_del_module(struct module *mod)
322{
323    struct jump_entry *iter_start = mod->jump_entries;
324    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
325    struct jump_entry *iter;
326    struct static_key *key = NULL;
327    struct static_key_mod *jlm, **prev;
328
329    for (iter = iter_start; iter < iter_stop; iter++) {
330        if (iter->key == (jump_label_t)(unsigned long)key)
331            continue;
332
333        key = (struct static_key *)(unsigned long)iter->key;
334
335        if (__module_address(iter->key) == mod)
336            continue;
337
338        prev = &key->next;
339        jlm = key->next;
340
341        while (jlm && jlm->mod != mod) {
342            prev = &jlm->next;
343            jlm = jlm->next;
344        }
345
346        if (jlm) {
347            *prev = jlm->next;
348            kfree(jlm);
349        }
350    }
351}
352
353static void jump_label_invalidate_module_init(struct module *mod)
354{
355    struct jump_entry *iter_start = mod->jump_entries;
356    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
357    struct jump_entry *iter;
358
359    for (iter = iter_start; iter < iter_stop; iter++) {
360        if (within_module_init(iter->code, mod))
361            iter->code = 0;
362    }
363}
364
365static int
366jump_label_module_notify(struct notifier_block *self, unsigned long val,
367             void *data)
368{
369    struct module *mod = data;
370    int ret = 0;
371
372    switch (val) {
373    case MODULE_STATE_COMING:
374        jump_label_lock();
375        ret = jump_label_add_module(mod);
376        if (ret)
377            jump_label_del_module(mod);
378        jump_label_unlock();
379        break;
380    case MODULE_STATE_GOING:
381        jump_label_lock();
382        jump_label_del_module(mod);
383        jump_label_unlock();
384        break;
385    case MODULE_STATE_LIVE:
386        jump_label_lock();
387        jump_label_invalidate_module_init(mod);
388        jump_label_unlock();
389        break;
390    }
391
392    return notifier_from_errno(ret);
393}
394
395struct notifier_block jump_label_module_nb = {
396    .notifier_call = jump_label_module_notify,
397    .priority = 1, /* higher than tracepoints */
398};
399
400static __init int jump_label_init_module(void)
401{
402    return register_module_notifier(&jump_label_module_nb);
403}
404early_initcall(jump_label_init_module);
405
406#endif /* CONFIG_MODULES */
407
408/***
409 * jump_label_text_reserved - check if addr range is reserved
410 * @start: start text addr
411 * @end: end text addr
412 *
413 * checks if the text addr located between @start and @end
414 * overlaps with any of the jump label patch addresses. Code
415 * that wants to modify kernel text should first verify that
416 * it does not overlap with any of the jump label addresses.
417 * Caller must hold jump_label_mutex.
418 *
419 * returns 1 if there is an overlap, 0 otherwise
420 */
421int jump_label_text_reserved(void *start, void *end)
422{
423    int ret = __jump_label_text_reserved(__start___jump_table,
424            __stop___jump_table, start, end);
425
426    if (ret)
427        return ret;
428
429#ifdef CONFIG_MODULES
430    ret = __jump_label_mod_text_reserved(start, end);
431#endif
432    return ret;
433}
434
435static void jump_label_update(struct static_key *key, int enable)
436{
437    struct jump_entry *stop = __stop___jump_table;
438    struct jump_entry *entry = jump_label_get_entries(key);
439
440#ifdef CONFIG_MODULES
441    struct module *mod = __module_address((unsigned long)key);
442
443    __jump_label_mod_update(key, enable);
444
445    if (mod)
446        stop = mod->jump_entries + mod->num_jump_entries;
447#endif
448    /* if there are no users, entry can be NULL */
449    if (entry)
450        __jump_label_update(key, entry, stop, enable);
451}
452
453#endif
454

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