Root/kernel/jump_label.c

1/*
2 * jump label support
3 *
4 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
5 *
6 */
7#include <linux/jump_label.h>
8#include <linux/memory.h>
9#include <linux/uaccess.h>
10#include <linux/module.h>
11#include <linux/list.h>
12#include <linux/jhash.h>
13#include <linux/slab.h>
14#include <linux/sort.h>
15#include <linux/err.h>
16
17#ifdef HAVE_JUMP_LABEL
18
19#define JUMP_LABEL_HASH_BITS 6
20#define JUMP_LABEL_TABLE_SIZE (1 << JUMP_LABEL_HASH_BITS)
21static struct hlist_head jump_label_table[JUMP_LABEL_TABLE_SIZE];
22
23/* mutex to protect coming/going of the the jump_label table */
24static DEFINE_MUTEX(jump_label_mutex);
25
26struct jump_label_entry {
27    struct hlist_node hlist;
28    struct jump_entry *table;
29    int nr_entries;
30    /* hang modules off here */
31    struct hlist_head modules;
32    unsigned long key;
33};
34
35struct jump_label_module_entry {
36    struct hlist_node hlist;
37    struct jump_entry *table;
38    int nr_entries;
39    struct module *mod;
40};
41
42void jump_label_lock(void)
43{
44    mutex_lock(&jump_label_mutex);
45}
46
47void jump_label_unlock(void)
48{
49    mutex_unlock(&jump_label_mutex);
50}
51
52static int jump_label_cmp(const void *a, const void *b)
53{
54    const struct jump_entry *jea = a;
55    const struct jump_entry *jeb = b;
56
57    if (jea->key < jeb->key)
58        return -1;
59
60    if (jea->key > jeb->key)
61        return 1;
62
63    return 0;
64}
65
66static void
67sort_jump_label_entries(struct jump_entry *start, struct jump_entry *stop)
68{
69    unsigned long size;
70
71    size = (((unsigned long)stop - (unsigned long)start)
72                    / sizeof(struct jump_entry));
73    sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
74}
75
76static struct jump_label_entry *get_jump_label_entry(jump_label_t key)
77{
78    struct hlist_head *head;
79    struct hlist_node *node;
80    struct jump_label_entry *e;
81    u32 hash = jhash((void *)&key, sizeof(jump_label_t), 0);
82
83    head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
84    hlist_for_each_entry(e, node, head, hlist) {
85        if (key == e->key)
86            return e;
87    }
88    return NULL;
89}
90
91static struct jump_label_entry *
92add_jump_label_entry(jump_label_t key, int nr_entries, struct jump_entry *table)
93{
94    struct hlist_head *head;
95    struct jump_label_entry *e;
96    u32 hash;
97
98    e = get_jump_label_entry(key);
99    if (e)
100        return ERR_PTR(-EEXIST);
101
102    e = kmalloc(sizeof(struct jump_label_entry), GFP_KERNEL);
103    if (!e)
104        return ERR_PTR(-ENOMEM);
105
106    hash = jhash((void *)&key, sizeof(jump_label_t), 0);
107    head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
108    e->key = key;
109    e->table = table;
110    e->nr_entries = nr_entries;
111    INIT_HLIST_HEAD(&(e->modules));
112    hlist_add_head(&e->hlist, head);
113    return e;
114}
115
116static int
117build_jump_label_hashtable(struct jump_entry *start, struct jump_entry *stop)
118{
119    struct jump_entry *iter, *iter_begin;
120    struct jump_label_entry *entry;
121    int count;
122
123    sort_jump_label_entries(start, stop);
124    iter = start;
125    while (iter < stop) {
126        entry = get_jump_label_entry(iter->key);
127        if (!entry) {
128            iter_begin = iter;
129            count = 0;
130            while ((iter < stop) &&
131                (iter->key == iter_begin->key)) {
132                iter++;
133                count++;
134            }
135            entry = add_jump_label_entry(iter_begin->key,
136                            count, iter_begin);
137            if (IS_ERR(entry))
138                return PTR_ERR(entry);
139         } else {
140            WARN_ONCE(1, KERN_ERR "build_jump_hashtable: unexpected entry!\n");
141            return -1;
142        }
143    }
144    return 0;
145}
146
147/***
148 * jump_label_update - update jump label text
149 * @key - key value associated with a a jump label
150 * @type - enum set to JUMP_LABEL_ENABLE or JUMP_LABEL_DISABLE
151 *
152 * Will enable/disable the jump for jump label @key, depending on the
153 * value of @type.
154 *
155 */
156
157void jump_label_update(unsigned long key, enum jump_label_type type)
158{
159    struct jump_entry *iter;
160    struct jump_label_entry *entry;
161    struct hlist_node *module_node;
162    struct jump_label_module_entry *e_module;
163    int count;
164
165    jump_label_lock();
166    entry = get_jump_label_entry((jump_label_t)key);
167    if (entry) {
168        count = entry->nr_entries;
169        iter = entry->table;
170        while (count--) {
171            if (kernel_text_address(iter->code))
172                arch_jump_label_transform(iter, type);
173            iter++;
174        }
175        /* eanble/disable jump labels in modules */
176        hlist_for_each_entry(e_module, module_node, &(entry->modules),
177                            hlist) {
178            count = e_module->nr_entries;
179            iter = e_module->table;
180            while (count--) {
181                if (iter->key &&
182                        kernel_text_address(iter->code))
183                    arch_jump_label_transform(iter, type);
184                iter++;
185            }
186        }
187    }
188    jump_label_unlock();
189}
190
191static int addr_conflict(struct jump_entry *entry, void *start, void *end)
192{
193    if (entry->code <= (unsigned long)end &&
194        entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
195        return 1;
196
197    return 0;
198}
199
200#ifdef CONFIG_MODULES
201
202static int module_conflict(void *start, void *end)
203{
204    struct hlist_head *head;
205    struct hlist_node *node, *node_next, *module_node, *module_node_next;
206    struct jump_label_entry *e;
207    struct jump_label_module_entry *e_module;
208    struct jump_entry *iter;
209    int i, count;
210    int conflict = 0;
211
212    for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
213        head = &jump_label_table[i];
214        hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
215            hlist_for_each_entry_safe(e_module, module_node,
216                            module_node_next,
217                            &(e->modules), hlist) {
218                count = e_module->nr_entries;
219                iter = e_module->table;
220                while (count--) {
221                    if (addr_conflict(iter, start, end)) {
222                        conflict = 1;
223                        goto out;
224                    }
225                    iter++;
226                }
227            }
228        }
229    }
230out:
231    return conflict;
232}
233
234#endif
235
236/***
237 * jump_label_text_reserved - check if addr range is reserved
238 * @start: start text addr
239 * @end: end text addr
240 *
241 * checks if the text addr located between @start and @end
242 * overlaps with any of the jump label patch addresses. Code
243 * that wants to modify kernel text should first verify that
244 * it does not overlap with any of the jump label addresses.
245 * Caller must hold jump_label_mutex.
246 *
247 * returns 1 if there is an overlap, 0 otherwise
248 */
249int jump_label_text_reserved(void *start, void *end)
250{
251    struct jump_entry *iter;
252    struct jump_entry *iter_start = __start___jump_table;
253    struct jump_entry *iter_stop = __start___jump_table;
254    int conflict = 0;
255
256    iter = iter_start;
257    while (iter < iter_stop) {
258        if (addr_conflict(iter, start, end)) {
259            conflict = 1;
260            goto out;
261        }
262        iter++;
263    }
264
265    /* now check modules */
266#ifdef CONFIG_MODULES
267    conflict = module_conflict(start, end);
268#endif
269out:
270    return conflict;
271}
272
273/*
274 * Not all archs need this.
275 */
276void __weak arch_jump_label_text_poke_early(jump_label_t addr)
277{
278}
279
280static __init int init_jump_label(void)
281{
282    int ret;
283    struct jump_entry *iter_start = __start___jump_table;
284    struct jump_entry *iter_stop = __stop___jump_table;
285    struct jump_entry *iter;
286
287    jump_label_lock();
288    ret = build_jump_label_hashtable(__start___jump_table,
289                     __stop___jump_table);
290    iter = iter_start;
291    while (iter < iter_stop) {
292        arch_jump_label_text_poke_early(iter->code);
293        iter++;
294    }
295    jump_label_unlock();
296    return ret;
297}
298early_initcall(init_jump_label);
299
300#ifdef CONFIG_MODULES
301
302static struct jump_label_module_entry *
303add_jump_label_module_entry(struct jump_label_entry *entry,
304                struct jump_entry *iter_begin,
305                int count, struct module *mod)
306{
307    struct jump_label_module_entry *e;
308
309    e = kmalloc(sizeof(struct jump_label_module_entry), GFP_KERNEL);
310    if (!e)
311        return ERR_PTR(-ENOMEM);
312    e->mod = mod;
313    e->nr_entries = count;
314    e->table = iter_begin;
315    hlist_add_head(&e->hlist, &entry->modules);
316    return e;
317}
318
319static int add_jump_label_module(struct module *mod)
320{
321    struct jump_entry *iter, *iter_begin;
322    struct jump_label_entry *entry;
323    struct jump_label_module_entry *module_entry;
324    int count;
325
326    /* if the module doesn't have jump label entries, just return */
327    if (!mod->num_jump_entries)
328        return 0;
329
330    sort_jump_label_entries(mod->jump_entries,
331                mod->jump_entries + mod->num_jump_entries);
332    iter = mod->jump_entries;
333    while (iter < mod->jump_entries + mod->num_jump_entries) {
334        entry = get_jump_label_entry(iter->key);
335        iter_begin = iter;
336        count = 0;
337        while ((iter < mod->jump_entries + mod->num_jump_entries) &&
338            (iter->key == iter_begin->key)) {
339                iter++;
340                count++;
341        }
342        if (!entry) {
343            entry = add_jump_label_entry(iter_begin->key, 0, NULL);
344            if (IS_ERR(entry))
345                return PTR_ERR(entry);
346        }
347        module_entry = add_jump_label_module_entry(entry, iter_begin,
348                               count, mod);
349        if (IS_ERR(module_entry))
350            return PTR_ERR(module_entry);
351    }
352    return 0;
353}
354
355static void remove_jump_label_module(struct module *mod)
356{
357    struct hlist_head *head;
358    struct hlist_node *node, *node_next, *module_node, *module_node_next;
359    struct jump_label_entry *e;
360    struct jump_label_module_entry *e_module;
361    int i;
362
363    /* if the module doesn't have jump label entries, just return */
364    if (!mod->num_jump_entries)
365        return;
366
367    for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
368        head = &jump_label_table[i];
369        hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
370            hlist_for_each_entry_safe(e_module, module_node,
371                          module_node_next,
372                          &(e->modules), hlist) {
373                if (e_module->mod == mod) {
374                    hlist_del(&e_module->hlist);
375                    kfree(e_module);
376                }
377            }
378            if (hlist_empty(&e->modules) && (e->nr_entries == 0)) {
379                hlist_del(&e->hlist);
380                kfree(e);
381            }
382        }
383    }
384}
385
386static void remove_jump_label_module_init(struct module *mod)
387{
388    struct hlist_head *head;
389    struct hlist_node *node, *node_next, *module_node, *module_node_next;
390    struct jump_label_entry *e;
391    struct jump_label_module_entry *e_module;
392    struct jump_entry *iter;
393    int i, count;
394
395    /* if the module doesn't have jump label entries, just return */
396    if (!mod->num_jump_entries)
397        return;
398
399    for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
400        head = &jump_label_table[i];
401        hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
402            hlist_for_each_entry_safe(e_module, module_node,
403                          module_node_next,
404                          &(e->modules), hlist) {
405                if (e_module->mod != mod)
406                    continue;
407                count = e_module->nr_entries;
408                iter = e_module->table;
409                while (count--) {
410                    if (within_module_init(iter->code, mod))
411                        iter->key = 0;
412                    iter++;
413                }
414            }
415        }
416    }
417}
418
419static int
420jump_label_module_notify(struct notifier_block *self, unsigned long val,
421             void *data)
422{
423    struct module *mod = data;
424    int ret = 0;
425
426    switch (val) {
427    case MODULE_STATE_COMING:
428        jump_label_lock();
429        ret = add_jump_label_module(mod);
430        if (ret)
431            remove_jump_label_module(mod);
432        jump_label_unlock();
433        break;
434    case MODULE_STATE_GOING:
435        jump_label_lock();
436        remove_jump_label_module(mod);
437        jump_label_unlock();
438        break;
439    case MODULE_STATE_LIVE:
440        jump_label_lock();
441        remove_jump_label_module_init(mod);
442        jump_label_unlock();
443        break;
444    }
445    return ret;
446}
447
448/***
449 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
450 * @mod: module to patch
451 *
452 * Allow for run-time selection of the optimal nops. Before the module
453 * loads patch these with arch_get_jump_label_nop(), which is specified by
454 * the arch specific jump label code.
455 */
456void jump_label_apply_nops(struct module *mod)
457{
458    struct jump_entry *iter;
459
460    /* if the module doesn't have jump label entries, just return */
461    if (!mod->num_jump_entries)
462        return;
463
464    iter = mod->jump_entries;
465    while (iter < mod->jump_entries + mod->num_jump_entries) {
466        arch_jump_label_text_poke_early(iter->code);
467        iter++;
468    }
469}
470
471struct notifier_block jump_label_module_nb = {
472    .notifier_call = jump_label_module_notify,
473    .priority = 0,
474};
475
476static __init int init_jump_label_module(void)
477{
478    return register_module_notifier(&jump_label_module_nb);
479}
480early_initcall(init_jump_label_module);
481
482#endif /* CONFIG_MODULES */
483
484#endif
485

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