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/jump_label.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
32bool jump_label_enabled(struct jump_label_key *key)
33{
34    return !!atomic_read(&key->enabled);
35}
36
37static int jump_label_cmp(const void *a, const void *b)
38{
39    const struct jump_entry *jea = a;
40    const struct jump_entry *jeb = b;
41
42    if (jea->key < jeb->key)
43        return -1;
44
45    if (jea->key > jeb->key)
46        return 1;
47
48    return 0;
49}
50
51static void
52jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
53{
54    unsigned long size;
55
56    size = (((unsigned long)stop - (unsigned long)start)
57                    / sizeof(struct jump_entry));
58    sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
59}
60
61static void jump_label_update(struct jump_label_key *key, int enable);
62
63void jump_label_inc(struct jump_label_key *key)
64{
65    if (atomic_inc_not_zero(&key->enabled))
66        return;
67
68    jump_label_lock();
69    if (atomic_add_return(1, &key->enabled) == 1)
70        jump_label_update(key, JUMP_LABEL_ENABLE);
71    jump_label_unlock();
72}
73
74void jump_label_dec(struct jump_label_key *key)
75{
76    if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
77        return;
78
79    jump_label_update(key, JUMP_LABEL_DISABLE);
80    jump_label_unlock();
81}
82
83static int addr_conflict(struct jump_entry *entry, void *start, void *end)
84{
85    if (entry->code <= (unsigned long)end &&
86        entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
87        return 1;
88
89    return 0;
90}
91
92static int __jump_label_text_reserved(struct jump_entry *iter_start,
93        struct jump_entry *iter_stop, void *start, void *end)
94{
95    struct jump_entry *iter;
96
97    iter = iter_start;
98    while (iter < iter_stop) {
99        if (addr_conflict(iter, start, end))
100            return 1;
101        iter++;
102    }
103
104    return 0;
105}
106
107static void __jump_label_update(struct jump_label_key *key,
108                struct jump_entry *entry,
109                struct jump_entry *stop, int enable)
110{
111    for (; (entry < stop) &&
112          (entry->key == (jump_label_t)(unsigned long)key);
113          entry++) {
114        /*
115         * entry->code set to 0 invalidates module init text sections
116         * kernel_text_address() verifies we are not in core kernel
117         * init code, see jump_label_invalidate_module_init().
118         */
119        if (entry->code && kernel_text_address(entry->code))
120            arch_jump_label_transform(entry, enable);
121    }
122}
123
124/*
125 * Not all archs need this.
126 */
127void __weak arch_jump_label_text_poke_early(jump_label_t addr)
128{
129}
130
131static __init int jump_label_init(void)
132{
133    struct jump_entry *iter_start = __start___jump_table;
134    struct jump_entry *iter_stop = __stop___jump_table;
135    struct jump_label_key *key = NULL;
136    struct jump_entry *iter;
137
138    jump_label_lock();
139    jump_label_sort_entries(iter_start, iter_stop);
140
141    for (iter = iter_start; iter < iter_stop; iter++) {
142        arch_jump_label_text_poke_early(iter->code);
143        if (iter->key == (jump_label_t)(unsigned long)key)
144            continue;
145
146        key = (struct jump_label_key *)(unsigned long)iter->key;
147        atomic_set(&key->enabled, 0);
148        key->entries = iter;
149#ifdef CONFIG_MODULES
150        key->next = NULL;
151#endif
152    }
153    jump_label_unlock();
154
155    return 0;
156}
157early_initcall(jump_label_init);
158
159#ifdef CONFIG_MODULES
160
161struct jump_label_mod {
162    struct jump_label_mod *next;
163    struct jump_entry *entries;
164    struct module *mod;
165};
166
167static int __jump_label_mod_text_reserved(void *start, void *end)
168{
169    struct module *mod;
170
171    mod = __module_text_address((unsigned long)start);
172    if (!mod)
173        return 0;
174
175    WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
176
177    return __jump_label_text_reserved(mod->jump_entries,
178                mod->jump_entries + mod->num_jump_entries,
179                start, end);
180}
181
182static void __jump_label_mod_update(struct jump_label_key *key, int enable)
183{
184    struct jump_label_mod *mod = key->next;
185
186    while (mod) {
187        struct module *m = mod->mod;
188
189        __jump_label_update(key, mod->entries,
190                    m->jump_entries + m->num_jump_entries,
191                    enable);
192        mod = mod->next;
193    }
194}
195
196/***
197 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
198 * @mod: module to patch
199 *
200 * Allow for run-time selection of the optimal nops. Before the module
201 * loads patch these with arch_get_jump_label_nop(), which is specified by
202 * the arch specific jump label code.
203 */
204void jump_label_apply_nops(struct module *mod)
205{
206    struct jump_entry *iter_start = mod->jump_entries;
207    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
208    struct jump_entry *iter;
209
210    /* if the module doesn't have jump label entries, just return */
211    if (iter_start == iter_stop)
212        return;
213
214    for (iter = iter_start; iter < iter_stop; iter++)
215        arch_jump_label_text_poke_early(iter->code);
216}
217
218static int jump_label_add_module(struct module *mod)
219{
220    struct jump_entry *iter_start = mod->jump_entries;
221    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
222    struct jump_entry *iter;
223    struct jump_label_key *key = NULL;
224    struct jump_label_mod *jlm;
225
226    /* if the module doesn't have jump label entries, just return */
227    if (iter_start == iter_stop)
228        return 0;
229
230    jump_label_sort_entries(iter_start, iter_stop);
231
232    for (iter = iter_start; iter < iter_stop; iter++) {
233        if (iter->key == (jump_label_t)(unsigned long)key)
234            continue;
235
236        key = (struct jump_label_key *)(unsigned long)iter->key;
237
238        if (__module_address(iter->key) == mod) {
239            atomic_set(&key->enabled, 0);
240            key->entries = iter;
241            key->next = NULL;
242            continue;
243        }
244
245        jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
246        if (!jlm)
247            return -ENOMEM;
248
249        jlm->mod = mod;
250        jlm->entries = iter;
251        jlm->next = key->next;
252        key->next = jlm;
253
254        if (jump_label_enabled(key))
255            __jump_label_update(key, iter, iter_stop,
256                        JUMP_LABEL_ENABLE);
257    }
258
259    return 0;
260}
261
262static void jump_label_del_module(struct module *mod)
263{
264    struct jump_entry *iter_start = mod->jump_entries;
265    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
266    struct jump_entry *iter;
267    struct jump_label_key *key = NULL;
268    struct jump_label_mod *jlm, **prev;
269
270    for (iter = iter_start; iter < iter_stop; iter++) {
271        if (iter->key == (jump_label_t)(unsigned long)key)
272            continue;
273
274        key = (struct jump_label_key *)(unsigned long)iter->key;
275
276        if (__module_address(iter->key) == mod)
277            continue;
278
279        prev = &key->next;
280        jlm = key->next;
281
282        while (jlm && jlm->mod != mod) {
283            prev = &jlm->next;
284            jlm = jlm->next;
285        }
286
287        if (jlm) {
288            *prev = jlm->next;
289            kfree(jlm);
290        }
291    }
292}
293
294static void jump_label_invalidate_module_init(struct module *mod)
295{
296    struct jump_entry *iter_start = mod->jump_entries;
297    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
298    struct jump_entry *iter;
299
300    for (iter = iter_start; iter < iter_stop; iter++) {
301        if (within_module_init(iter->code, mod))
302            iter->code = 0;
303    }
304}
305
306static int
307jump_label_module_notify(struct notifier_block *self, unsigned long val,
308             void *data)
309{
310    struct module *mod = data;
311    int ret = 0;
312
313    switch (val) {
314    case MODULE_STATE_COMING:
315        jump_label_lock();
316        ret = jump_label_add_module(mod);
317        if (ret)
318            jump_label_del_module(mod);
319        jump_label_unlock();
320        break;
321    case MODULE_STATE_GOING:
322        jump_label_lock();
323        jump_label_del_module(mod);
324        jump_label_unlock();
325        break;
326    case MODULE_STATE_LIVE:
327        jump_label_lock();
328        jump_label_invalidate_module_init(mod);
329        jump_label_unlock();
330        break;
331    }
332
333    return notifier_from_errno(ret);
334}
335
336struct notifier_block jump_label_module_nb = {
337    .notifier_call = jump_label_module_notify,
338    .priority = 1, /* higher than tracepoints */
339};
340
341static __init int jump_label_init_module(void)
342{
343    return register_module_notifier(&jump_label_module_nb);
344}
345early_initcall(jump_label_init_module);
346
347#endif /* CONFIG_MODULES */
348
349/***
350 * jump_label_text_reserved - check if addr range is reserved
351 * @start: start text addr
352 * @end: end text addr
353 *
354 * checks if the text addr located between @start and @end
355 * overlaps with any of the jump label patch addresses. Code
356 * that wants to modify kernel text should first verify that
357 * it does not overlap with any of the jump label addresses.
358 * Caller must hold jump_label_mutex.
359 *
360 * returns 1 if there is an overlap, 0 otherwise
361 */
362int jump_label_text_reserved(void *start, void *end)
363{
364    int ret = __jump_label_text_reserved(__start___jump_table,
365            __stop___jump_table, start, end);
366
367    if (ret)
368        return ret;
369
370#ifdef CONFIG_MODULES
371    ret = __jump_label_mod_text_reserved(start, end);
372#endif
373    return ret;
374}
375
376static void jump_label_update(struct jump_label_key *key, int enable)
377{
378    struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
379
380#ifdef CONFIG_MODULES
381    struct module *mod = __module_address((jump_label_t)key);
382
383    __jump_label_mod_update(key, enable);
384
385    if (mod)
386        stop = mod->jump_entries + mod->num_jump_entries;
387#endif
388    /* if there are no users, entry can be NULL */
389    if (entry)
390        __jump_label_update(key, entry, stop, enable);
391}
392
393#endif
394

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