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