kernel/kprobes.c

   1 /*
   2  *  Kernel Probes (KProbes)
   3  *  kernel/kprobes.c
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  18  *
  19  * Copyright (C) IBM Corporation, 2002, 2004
  20  *
  21  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  22  *              Probes initial implementation (includes suggestions from
  23  *              Rusty Russell).
  24  * 2004-Aug     Updated by Prasanna S Panchamukhi <prasanna@in.ibm.com> with
  25  *              hlists and exceptions notifier as suggested by Andi Kleen.
  26  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  27  *              interface to access function arguments.
  28  * 2004-Sep     Prasanna S Panchamukhi <prasanna@in.ibm.com> Changed Kprobes
  29  *              exceptions notifier to be first on the priority list.
  30  * 2005-May     Hien Nguyen <hien@us.ibm.com>, Jim Keniston
  31  *              <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
  32  *              <prasanna@in.ibm.com> added function-return probes.
  33  */
  34 #include <linux/kprobes.h>
  35 #include <linux/hash.h>
  36 #include <linux/init.h>
  37 #include <linux/slab.h>
  38 #include <linux/module.h>
  39 #include <linux/moduleloader.h>
  40 #include <linux/kallsyms.h>
  41 #include <asm-generic/sections.h>
  42 #include <asm/cacheflush.h>
  43 #include <asm/errno.h>
  44 #include <asm/kdebug.h>
  45
  46 #define KPROBE_HASH_BITS 6
  47 #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
  48
  49
  50 /*
  51  * Some oddball architectures like 64bit powerpc have function descriptors
  52  * so this must be overridable.
  53  */
  54 #ifndef kprobe_lookup_name
  55 #define kprobe_lookup_name(name, addr) \
  56         addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
  57 #endif
  58
  59 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
  60 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
  61 static atomic_t kprobe_count;
  62
  63 DEFINE_MUTEX(kprobe_mutex);             /* Protects kprobe_table */
  64 DEFINE_SPINLOCK(kretprobe_lock);        /* Protects kretprobe_inst_table */
  65 static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
  66
  67 static struct notifier_block kprobe_page_fault_nb = {
  68         .notifier_call = kprobe_exceptions_notify,
  69         .priority = 0x7fffffff /* we need to notified first */
  70 };
  71
  72 #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
  73 /*
  74  * kprobe->ainsn.insn points to the copy of the instruction to be
  75  * single-stepped. x86_64, POWER4 and above have no-exec support and
  76  * stepping on the instruction on a vmalloced/kmalloced/data page
  77  * is a recipe for disaster
  78  */
  79 #define INSNS_PER_PAGE  (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
  80
  81 struct kprobe_insn_page {
  82         struct hlist_node hlist;
  83         kprobe_opcode_t *insns;         /* Page of instruction slots */
  84         char slot_used[INSNS_PER_PAGE];
  85         int nused;
  86 };
  87
  88 static struct hlist_head kprobe_insn_pages;
  89
  90 /**
  91  * get_insn_slot() - Find a slot on an executable page for an instruction.
  92  * We allocate an executable page if there's no room on existing ones.
  93  */
  94 kprobe_opcode_t __kprobes *get_insn_slot(void)
  95 {
  96         struct kprobe_insn_page *kip;
  97         struct hlist_node *pos;
  98
  99         hlist_for_each(pos, &kprobe_insn_pages) {
 100                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
 101                 if (kip->nused < INSNS_PER_PAGE) {
 102                         int i;
 103                         for (i = 0; i < INSNS_PER_PAGE; i++) {
 104                                 if (!kip->slot_used[i]) {
 105                                         kip->slot_used[i] = 1;
 106                                         kip->nused++;
 107                                         return kip->insns + (i * MAX_INSN_SIZE);
 108                                 }
 109                         }
 110                         /* Surprise!  No unused slots.  Fix kip->nused. */
 111                         kip->nused = INSNS_PER_PAGE;
 112                 }
 113         }
 114
 115         /* All out of space.  Need to allocate a new page. Use slot 0.*/
 116         kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
 117         if (!kip) {
 118                 return NULL;
 119         }
 120
 121         /*
 122          * Use module_alloc so this page is within +/- 2GB of where the
 123          * kernel image and loaded module images reside. This is required
 124          * so x86_64 can correctly handle the %rip-relative fixups.
 125          */
 126         kip->insns = module_alloc(PAGE_SIZE);
 127         if (!kip->insns) {
 128                 kfree(kip);
 129                 return NULL;
 130         }
 131         INIT_HLIST_NODE(&kip->hlist);
 132         hlist_add_head(&kip->hlist, &kprobe_insn_pages);
 133         memset(kip->slot_used, 0, INSNS_PER_PAGE);
 134         kip->slot_used[0] = 1;
 135         kip->nused = 1;
 136         return kip->insns;
 137 }
 138
 139 void __kprobes free_insn_slot(kprobe_opcode_t *slot)
 140 {
 141         struct kprobe_insn_page *kip;
 142         struct hlist_node *pos;
 143
 144         hlist_for_each(pos, &kprobe_insn_pages) {
 145                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
 146                 if (kip->insns <= slot &&
 147                     slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
 148                         int i = (slot - kip->insns) / MAX_INSN_SIZE;
 149                         kip->slot_used[i] = 0;
 150                         kip->nused--;
 151                         if (kip->nused == 0) {
 152                                 /*
 153                                  * Page is no longer in use.  Free it unless
 154                                  * it's the last one.  We keep the last one
 155                                  * so as not to have to set it up again the
 156                                  * next time somebody inserts a probe.
 157                                  */
 158                                 hlist_del(&kip->hlist);
 159                                 if (hlist_empty(&kprobe_insn_pages)) {
 160                                         INIT_HLIST_NODE(&kip->hlist);
 161                                         hlist_add_head(&kip->hlist,
 162                                                 &kprobe_insn_pages);
 163                                 } else {
 164                                         module_free(NULL, kip->insns);
 165                                         kfree(kip);
 166                                 }
 167                         }
 168                         return;
 169                 }
 170         }
 171 }
 172 #endif
 173
 174 /* We have preemption disabled.. so it is safe to use __ versions */
 175 static inline void set_kprobe_instance(struct kprobe *kp)
 176 {
 177         __get_cpu_var(kprobe_instance) = kp;
 178 }
 179
 180 static inline void reset_kprobe_instance(void)
 181 {
 182         __get_cpu_var(kprobe_instance) = NULL;
 183 }
 184
 185 /*
 186  * This routine is called either:
 187  *      - under the kprobe_mutex - during kprobe_[un]register()
 188  *                              OR
 189  *      - with preemption disabled - from arch/xxx/kernel/kprobes.c
 190  */
 191 struct kprobe __kprobes *get_kprobe(void *addr)
 192 {
 193         struct hlist_head *head;
 194         struct hlist_node *node;
 195         struct kprobe *p;
 196
 197         head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
 198         hlist_for_each_entry_rcu(p, node, head, hlist) {
 199                 if (p->addr == addr)
 200                         return p;
 201         }
 202         return NULL;
 203 }
 204
 205 /*
 206  * Aggregate handlers for multiple kprobes support - these handlers
 207  * take care of invoking the individual kprobe handlers on p->list
 208  */
 209 static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
 210 {
 211         struct kprobe *kp;
 212
 213         list_for_each_entry_rcu(kp, &p->list, list) {
 214                 if (kp->pre_handler) {
 215                         set_kprobe_instance(kp);
 216                         if (kp->pre_handler(kp, regs))
 217                                 return 1;
 218                 }
 219                 reset_kprobe_instance();
 220         }
 221         return 0;
 222 }
 223
 224 static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
 225                                         unsigned long flags)
 226 {
 227         struct kprobe *kp;
 228
 229         list_for_each_entry_rcu(kp, &p->list, list) {
 230                 if (kp->post_handler) {
 231                         set_kprobe_instance(kp);
 232                         kp->post_handler(kp, regs, flags);
 233                         reset_kprobe_instance();
 234                 }
 235         }
 236         return;
 237 }
 238
 239 static int __kprobes aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
 240                                         int trapnr)
 241 {
 242         struct kprobe *cur = __get_cpu_var(kprobe_instance);
 243
 244         /*
 245          * if we faulted "during" the execution of a user specified
 246          * probe handler, invoke just that probe's fault handler
 247          */
 248         if (cur && cur->fault_handler) {
 249                 if (cur->fault_handler(cur, regs, trapnr))
 250                         return 1;
 251         }
 252         return 0;
 253 }
 254
 255 static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
 256 {
 257         struct kprobe *cur = __get_cpu_var(kprobe_instance);
 258         int ret = 0;
 259
 260         if (cur && cur->break_handler) {
 261                 if (cur->break_handler(cur, regs))
 262                         ret = 1;
 263         }
 264         reset_kprobe_instance();
 265         return ret;
 266 }
 267
 268 /* Walks the list and increments nmissed count for multiprobe case */
 269 void __kprobes kprobes_inc_nmissed_count(struct kprobe *p)
 270 {
 271         struct kprobe *kp;
 272         if (p->pre_handler != aggr_pre_handler) {
 273                 p->nmissed++;
 274         } else {
 275                 list_for_each_entry_rcu(kp, &p->list, list)
 276                         kp->nmissed++;
 277         }
 278         return;
 279 }
 280
 281 /* Called with kretprobe_lock held */
 282 struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
 283 {
 284         struct hlist_node *node;
 285         struct kretprobe_instance *ri;
 286         hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
 287                 return ri;
 288         return NULL;
 289 }
 290
 291 /* Called with kretprobe_lock held */
 292 static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
 293                                                               *rp)
 294 {
 295         struct hlist_node *node;
 296         struct kretprobe_instance *ri;
 297         hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
 298                 return ri;
 299         return NULL;
 300 }
 301
 302 /* Called with kretprobe_lock held */
 303 void __kprobes add_rp_inst(struct kretprobe_instance *ri)
 304 {
 305         /*
 306          * Remove rp inst off the free list -
 307          * Add it back when probed function returns
 308          */
 309         hlist_del(&ri->uflist);
 310
 311         /* Add rp inst onto table */
 312         INIT_HLIST_NODE(&ri->hlist);
 313         hlist_add_head(&ri->hlist,
 314                         &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);
 315
 316         /* Also add this rp inst to the used list. */
 317         INIT_HLIST_NODE(&ri->uflist);
 318         hlist_add_head(&ri->uflist, &ri->rp->used_instances);
 319 }
 320
 321 /* Called with kretprobe_lock held */
 322 void __kprobes recycle_rp_inst(struct kretprobe_instance *ri)
 323 {
 324         /* remove rp inst off the rprobe_inst_table */
 325         hlist_del(&ri->hlist);
 326         if (ri->rp) {
 327                 /* remove rp inst off the used list */
 328                 hlist_del(&ri->uflist);
 329                 /* put rp inst back onto the free list */
 330                 INIT_HLIST_NODE(&ri->uflist);
 331                 hlist_add_head(&ri->uflist, &ri->rp->free_instances);
 332         } else
 333                 /* Unregistering */
 334                 kfree(ri);
 335 }
 336
 337 struct hlist_head __kprobes *kretprobe_inst_table_head(struct task_struct *tsk)
 338 {
 339         return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
 340 }
 341
 342 /*
 343  * This function is called from finish_task_switch when task tk becomes dead,
 344  * so that we can recycle any function-return probe instances associated
 345  * with this task. These left over instances represent probed functions
 346  * that have been called but will never return.
 347  */
 348 void __kprobes kprobe_flush_task(struct task_struct *tk)
 349 {
 350         struct kretprobe_instance *ri;
 351         struct hlist_head *head;
 352         struct hlist_node *node, *tmp;
 353         unsigned long flags = 0;
 354
 355         spin_lock_irqsave(&kretprobe_lock, flags);
 356         head = kretprobe_inst_table_head(tk);
 357         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 358                 if (ri->task == tk)
 359                         recycle_rp_inst(ri);
 360         }
 361         spin_unlock_irqrestore(&kretprobe_lock, flags);
 362 }
 363
 364 static inline void free_rp_inst(struct kretprobe *rp)
 365 {
 366         struct kretprobe_instance *ri;
 367         while ((ri = get_free_rp_inst(rp)) != NULL) {
 368                 hlist_del(&ri->uflist);
 369                 kfree(ri);
 370         }
 371 }
 372
 373 /*
 374  * Keep all fields in the kprobe consistent
 375  */
 376 static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
 377 {
 378         memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
 379         memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
 380 }
 381
 382 /*
 383 * Add the new probe to old_p->list. Fail if this is the
 384 * second jprobe at the address - two jprobes can't coexist
 385 */
 386 static int __kprobes add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
 387 {
 388         if (p->break_handler) {
 389                 if (old_p->break_handler)
 390                         return -EEXIST;
 391                 list_add_tail_rcu(&p->list, &old_p->list);
 392                 old_p->break_handler = aggr_break_handler;
 393         } else
 394                 list_add_rcu(&p->list, &old_p->list);
 395         if (p->post_handler && !old_p->post_handler)
 396                 old_p->post_handler = aggr_post_handler;
 397         return 0;
 398 }
 399
 400 /*
 401  * Fill in the required fields of the "manager kprobe". Replace the
 402  * earlier kprobe in the hlist with the manager kprobe
 403  */
 404 static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 405 {
 406         copy_kprobe(p, ap);
 407         flush_insn_slot(ap);
 408         ap->addr = p->addr;
 409         ap->pre_handler = aggr_pre_handler;
 410         ap->fault_handler = aggr_fault_handler;
 411         if (p->post_handler)
 412                 ap->post_handler = aggr_post_handler;
 413         if (p->break_handler)
 414                 ap->break_handler = aggr_break_handler;
 415
 416         INIT_LIST_HEAD(&ap->list);
 417         list_add_rcu(&p->list, &ap->list);
 418
 419         hlist_replace_rcu(&p->hlist, &ap->hlist);
 420 }
 421
 422 /*
 423  * This is the second or subsequent kprobe at the address - handle
 424  * the intricacies
 425  */
 426 static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
 427                                           struct kprobe *p)
 428 {
 429         int ret = 0;
 430         struct kprobe *ap;
 431
 432         if (old_p->pre_handler == aggr_pre_handler) {
 433                 copy_kprobe(old_p, p);
 434                 ret = add_new_kprobe(old_p, p);
 435         } else {
 436                 ap = kzalloc(sizeof(struct kprobe), GFP_KERNEL);
 437                 if (!ap)
 438                         return -ENOMEM;
 439                 add_aggr_kprobe(ap, old_p);
 440                 copy_kprobe(ap, p);
 441                 ret = add_new_kprobe(ap, p);
 442         }
 443         return ret;
 444 }
 445
 446 static int __kprobes in_kprobes_functions(unsigned long addr)
 447 {
 448         if (addr >= (unsigned long)__kprobes_text_start
 449                 && addr < (unsigned long)__kprobes_text_end)
 450                 return -EINVAL;
 451         return 0;
 452 }
 453
 454 static int __kprobes __register_kprobe(struct kprobe *p,
 455         unsigned long called_from)
 456 {
 457         int ret = 0;
 458         struct kprobe *old_p;
 459         struct module *probed_mod;
 460
 461         /*
 462          * If we have a symbol_name argument look it up,
 463          * and add it to the address.  That way the addr
 464          * field can either be global or relative to a symbol.
 465          */
 466         if (p->symbol_name) {
 467                 if (p->addr)
 468                         return -EINVAL;
 469                 kprobe_lookup_name(p->symbol_name, p->addr);
 470         }
 471
 472         if (!p->addr)
 473                 return -EINVAL;
 474         p->addr = (kprobe_opcode_t *)(((char *)p->addr)+ p->offset);
 475
 476         if ((!kernel_text_address((unsigned long) p->addr)) ||
 477                 in_kprobes_functions((unsigned long) p->addr))
 478                 return -EINVAL;
 479
 480         p->mod_refcounted = 0;
 481         /* Check are we probing a module */
 482         if ((probed_mod = module_text_address((unsigned long) p->addr))) {
 483                 struct module *calling_mod = module_text_address(called_from);
 484                 /* We must allow modules to probe themself and
 485                  * in this case avoid incrementing the module refcount,
 486                  * so as to allow unloading of self probing modules.
 487                  */
 488                 if (calling_mod && (calling_mod != probed_mod)) {
 489                         if (unlikely(!try_module_get(probed_mod)))
 490                                 return -EINVAL;
 491                         p->mod_refcounted = 1;
 492                 } else
 493                         probed_mod = NULL;
 494         }
 495
 496         p->nmissed = 0;
 497         mutex_lock(&kprobe_mutex);
 498         old_p = get_kprobe(p->addr);
 499         if (old_p) {
 500                 ret = register_aggr_kprobe(old_p, p);
 501                 if (!ret)
 502                         atomic_inc(&kprobe_count);
 503                 goto out;
 504         }
 505
 506         if ((ret = arch_prepare_kprobe(p)) != 0)
 507                 goto out;
 508
 509         INIT_HLIST_NODE(&p->hlist);
 510         hlist_add_head_rcu(&p->hlist,
 511                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 512
 513         if (atomic_add_return(1, &kprobe_count) == \
 514                                 (ARCH_INACTIVE_KPROBE_COUNT + 1))
 515                 register_page_fault_notifier(&kprobe_page_fault_nb);
 516
 517         arch_arm_kprobe(p);
 518
 519 out:
 520         mutex_unlock(&kprobe_mutex);
 521
 522         if (ret && probed_mod)
 523                 module_put(probed_mod);
 524         return ret;
 525 }
 526
 527 int __kprobes register_kprobe(struct kprobe *p)
 528 {
 529         return __register_kprobe(p,
 530                 (unsigned long)__builtin_return_address(0));
 531 }
 532
 533 void __kprobes unregister_kprobe(struct kprobe *p)
 534 {
 535         struct module *mod;
 536         struct kprobe *old_p, *list_p;
 537         int cleanup_p;
 538
 539         mutex_lock(&kprobe_mutex);
 540         old_p = get_kprobe(p->addr);
 541         if (unlikely(!old_p)) {
 542                 mutex_unlock(&kprobe_mutex);
 543                 return;
 544         }
 545         if (p != old_p) {
 546                 list_for_each_entry_rcu(list_p, &old_p->list, list)
 547                         if (list_p == p)
 548                         /* kprobe p is a valid probe */
 549                                 goto valid_p;
 550                 mutex_unlock(&kprobe_mutex);
 551                 return;
 552         }
 553 valid_p:
 554         if ((old_p == p) || ((old_p->pre_handler == aggr_pre_handler) &&
 555                 (p->list.next == &old_p->list) &&
 556                 (p->list.prev == &old_p->list))) {
 557                 /* Only probe on the hash list */
 558                 arch_disarm_kprobe(p);
 559                 hlist_del_rcu(&old_p->hlist);
 560                 cleanup_p = 1;
 561         } else {
 562                 list_del_rcu(&p->list);
 563                 cleanup_p = 0;
 564         }
 565
 566         mutex_unlock(&kprobe_mutex);
 567
 568         synchronize_sched();
 569         if (p->mod_refcounted &&
 570             (mod = module_text_address((unsigned long)p->addr)))
 571                 module_put(mod);
 572
 573         if (cleanup_p) {
 574                 if (p != old_p) {
 575                         list_del_rcu(&p->list);
 576                         kfree(old_p);
 577                 }
 578                 arch_remove_kprobe(p);
 579         } else {
 580                 mutex_lock(&kprobe_mutex);
 581                 if (p->break_handler)
 582                         old_p->break_handler = NULL;
 583                 if (p->post_handler){
 584                         list_for_each_entry_rcu(list_p, &old_p->list, list){
 585                                 if (list_p->post_handler){
 586                                         cleanup_p = 2;
 587                                         break;
 588                                 }
 589                         }
 590                         if (cleanup_p == 0)
 591                                 old_p->post_handler = NULL;
 592                 }
 593                 mutex_unlock(&kprobe_mutex);
 594         }
 595
 596         /* Call unregister_page_fault_notifier()
 597          * if no probes are active
 598          */
 599         mutex_lock(&kprobe_mutex);
 600         if (atomic_add_return(-1, &kprobe_count) == \
 601                                 ARCH_INACTIVE_KPROBE_COUNT)
 602                 unregister_page_fault_notifier(&kprobe_page_fault_nb);
 603         mutex_unlock(&kprobe_mutex);
 604         return;
 605 }
 606
 607 static struct notifier_block kprobe_exceptions_nb = {
 608         .notifier_call = kprobe_exceptions_notify,
 609         .priority = 0x7fffffff /* we need to be notified first */
 610 };
 611
 612
 613 int __kprobes register_jprobe(struct jprobe *jp)
 614 {
 615         /* Todo: Verify probepoint is a function entry point */
 616         jp->kp.pre_handler = setjmp_pre_handler;
 617         jp->kp.break_handler = longjmp_break_handler;
 618
 619         return __register_kprobe(&jp->kp,
 620                 (unsigned long)__builtin_return_address(0));
 621 }
 622
 623 void __kprobes unregister_jprobe(struct jprobe *jp)
 624 {
 625         unregister_kprobe(&jp->kp);
 626 }
 627
 628 #ifdef ARCH_SUPPORTS_KRETPROBES
 629
 630 /*
 631  * This kprobe pre_handler is registered with every kretprobe. When probe
 632  * hits it will set up the return probe.
 633  */
 634 static int __kprobes pre_handler_kretprobe(struct kprobe *p,
 635                                            struct pt_regs *regs)
 636 {
 637         struct kretprobe *rp = container_of(p, struct kretprobe, kp);
 638         unsigned long flags = 0;
 639
 640         /*TODO: consider to only swap the RA after the last pre_handler fired */
 641         spin_lock_irqsave(&kretprobe_lock, flags);
 642         arch_prepare_kretprobe(rp, regs);
 643         spin_unlock_irqrestore(&kretprobe_lock, flags);
 644         return 0;
 645 }
 646
 647 int __kprobes register_kretprobe(struct kretprobe *rp)
 648 {
 649         int ret = 0;
 650         struct kretprobe_instance *inst;
 651         int i;
 652
 653         rp->kp.pre_handler = pre_handler_kretprobe;
 654         rp->kp.post_handler = NULL;
 655         rp->kp.fault_handler = NULL;
 656         rp->kp.break_handler = NULL;
 657
 658         /* Pre-allocate memory for max kretprobe instances */
 659         if (rp->maxactive <= 0) {
 660 #ifdef CONFIG_PREEMPT
 661                 rp->maxactive = max(10, 2 * NR_CPUS);
 662 #else
 663                 rp->maxactive = NR_CPUS;
 664 #endif
 665         }
 666         INIT_HLIST_HEAD(&rp->used_instances);
 667         INIT_HLIST_HEAD(&rp->free_instances);
 668         for (i = 0; i < rp->maxactive; i++) {
 669                 inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
 670                 if (inst == NULL) {
 671                         free_rp_inst(rp);
 672                         return -ENOMEM;
 673                 }
 674                 INIT_HLIST_NODE(&inst->uflist);
 675                 hlist_add_head(&inst->uflist, &rp->free_instances);
 676         }
 677
 678         rp->nmissed = 0;
 679         /* Establish function entry probe point */
 680         if ((ret = __register_kprobe(&rp->kp,
 681                 (unsigned long)__builtin_return_address(0))) != 0)
 682                 free_rp_inst(rp);
 683         return ret;
 684 }
 685
 686 #else /* ARCH_SUPPORTS_KRETPROBES */
 687
 688 int __kprobes register_kretprobe(struct kretprobe *rp)
 689 {
 690         return -ENOSYS;
 691 }
 692
 693 #endif /* ARCH_SUPPORTS_KRETPROBES */
 694
 695 void __kprobes unregister_kretprobe(struct kretprobe *rp)
 696 {
 697         unsigned long flags;
 698         struct kretprobe_instance *ri;
 699
 700         unregister_kprobe(&rp->kp);
 701         /* No race here */
 702         spin_lock_irqsave(&kretprobe_lock, flags);
 703         while ((ri = get_used_rp_inst(rp)) != NULL) {
 704                 ri->rp = NULL;
 705                 hlist_del(&ri->uflist);
 706         }
 707         spin_unlock_irqrestore(&kretprobe_lock, flags);
 708         free_rp_inst(rp);
 709 }
 710
 711 static int __init init_kprobes(void)
 712 {
 713         int i, err = 0;
 714
 715         /* FIXME allocate the probe table, currently defined statically */
 716         /* initialize all list heads */
 717         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 718                 INIT_HLIST_HEAD(&kprobe_table[i]);
 719                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
 720         }
 721         atomic_set(&kprobe_count, 0);
 722
 723         err = arch_init_kprobes();
 724         if (!err)
 725                 err = register_die_notifier(&kprobe_exceptions_nb);
 726
 727         return err;
 728 }
 729
 730 __initcall(init_kprobes);
 731
 732 EXPORT_SYMBOL_GPL(register_kprobe);
 733 EXPORT_SYMBOL_GPL(unregister_kprobe);
 734 EXPORT_SYMBOL_GPL(register_jprobe);
 735 EXPORT_SYMBOL_GPL(unregister_jprobe);
 736 EXPORT_SYMBOL_GPL(jprobe_return);
 737 EXPORT_SYMBOL_GPL(register_kretprobe);
 738 EXPORT_SYMBOL_GPL(unregister_kretprobe);
 739