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/spinlock.h>
  36 #include <linux/hash.h>
  37 #include <linux/init.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
  51 unsigned int kprobe_cpu = NR_CPUS;
  52 static DEFINE_SPINLOCK(kprobe_lock);
  53 static struct kprobe *curr_kprobe;
  54
  55 /*
  56  * kprobe->ainsn.insn points to the copy of the instruction to be
  57  * single-stepped. x86_64, POWER4 and above have no-exec support and
  58  * stepping on the instruction on a vmalloced/kmalloced/data page
  59  * is a recipe for disaster
  60  */
  61 #define INSNS_PER_PAGE  (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
  62
  63 struct kprobe_insn_page {
  64         struct hlist_node hlist;
  65         kprobe_opcode_t *insns;         /* Page of instruction slots */
  66         char slot_used[INSNS_PER_PAGE];
  67         int nused;
  68 };
  69
  70 static struct hlist_head kprobe_insn_pages;
  71
  72 /**
  73  * get_insn_slot() - Find a slot on an executable page for an instruction.
  74  * We allocate an executable page if there's no room on existing ones.
  75  */
  76 kprobe_opcode_t __kprobes *get_insn_slot(void)
  77 {
  78         struct kprobe_insn_page *kip;
  79         struct hlist_node *pos;
  80
  81         hlist_for_each(pos, &kprobe_insn_pages) {
  82                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
  83                 if (kip->nused < INSNS_PER_PAGE) {
  84                         int i;
  85                         for (i = 0; i < INSNS_PER_PAGE; i++) {
  86                                 if (!kip->slot_used[i]) {
  87                                         kip->slot_used[i] = 1;
  88                                         kip->nused++;
  89                                         return kip->insns + (i * MAX_INSN_SIZE);
  90                                 }
  91                         }
  92                         /* Surprise!  No unused slots.  Fix kip->nused. */
  93                         kip->nused = INSNS_PER_PAGE;
  94                 }
  95         }
  96
  97         /* All out of space.  Need to allocate a new page. Use slot 0.*/
  98         kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
  99         if (!kip) {
 100                 return NULL;
 101         }
 102
 103         /*
 104          * Use module_alloc so this page is within +/- 2GB of where the
 105          * kernel image and loaded module images reside. This is required
 106          * so x86_64 can correctly handle the %rip-relative fixups.
 107          */
 108         kip->insns = module_alloc(PAGE_SIZE);
 109         if (!kip->insns) {
 110                 kfree(kip);
 111                 return NULL;
 112         }
 113         INIT_HLIST_NODE(&kip->hlist);
 114         hlist_add_head(&kip->hlist, &kprobe_insn_pages);
 115         memset(kip->slot_used, 0, INSNS_PER_PAGE);
 116         kip->slot_used[0] = 1;
 117         kip->nused = 1;
 118         return kip->insns;
 119 }
 120
 121 void __kprobes free_insn_slot(kprobe_opcode_t *slot)
 122 {
 123         struct kprobe_insn_page *kip;
 124         struct hlist_node *pos;
 125
 126         hlist_for_each(pos, &kprobe_insn_pages) {
 127                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
 128                 if (kip->insns <= slot &&
 129                     slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
 130                         int i = (slot - kip->insns) / MAX_INSN_SIZE;
 131                         kip->slot_used[i] = 0;
 132                         kip->nused--;
 133                         if (kip->nused == 0) {
 134                                 /*
 135                                  * Page is no longer in use.  Free it unless
 136                                  * it's the last one.  We keep the last one
 137                                  * so as not to have to set it up again the
 138                                  * next time somebody inserts a probe.
 139                                  */
 140                                 hlist_del(&kip->hlist);
 141                                 if (hlist_empty(&kprobe_insn_pages)) {
 142                                         INIT_HLIST_NODE(&kip->hlist);
 143                                         hlist_add_head(&kip->hlist,
 144                                                 &kprobe_insn_pages);
 145                                 } else {
 146                                         module_free(NULL, kip->insns);
 147                                         kfree(kip);
 148                                 }
 149                         }
 150                         return;
 151                 }
 152         }
 153 }
 154
 155 /* Locks kprobe: irqs must be disabled */
 156 void __kprobes lock_kprobes(void)
 157 {
 158         spin_lock(&kprobe_lock);
 159         kprobe_cpu = smp_processor_id();
 160 }
 161
 162 void __kprobes unlock_kprobes(void)
 163 {
 164         kprobe_cpu = NR_CPUS;
 165         spin_unlock(&kprobe_lock);
 166 }
 167
 168 /* You have to be holding the kprobe_lock */
 169 struct kprobe __kprobes *get_kprobe(void *addr)
 170 {
 171         struct hlist_head *head;
 172         struct hlist_node *node;
 173
 174         head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
 175         hlist_for_each(node, head) {
 176                 struct kprobe *p = hlist_entry(node, struct kprobe, hlist);
 177                 if (p->addr == addr)
 178                         return p;
 179         }
 180         return NULL;
 181 }
 182
 183 /*
 184  * Aggregate handlers for multiple kprobes support - these handlers
 185  * take care of invoking the individual kprobe handlers on p->list
 186  */
 187 static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
 188 {
 189         struct kprobe *kp;
 190
 191         list_for_each_entry(kp, &p->list, list) {
 192                 if (kp->pre_handler) {
 193                         curr_kprobe = kp;
 194                         if (kp->pre_handler(kp, regs))
 195                                 return 1;
 196                 }
 197                 curr_kprobe = NULL;
 198         }
 199         return 0;
 200 }
 201
 202 static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
 203                                         unsigned long flags)
 204 {
 205         struct kprobe *kp;
 206
 207         list_for_each_entry(kp, &p->list, list) {
 208                 if (kp->post_handler) {
 209                         curr_kprobe = kp;
 210                         kp->post_handler(kp, regs, flags);
 211                         curr_kprobe = NULL;
 212                 }
 213         }
 214         return;
 215 }
 216
 217 static int __kprobes aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
 218                                         int trapnr)
 219 {
 220         /*
 221          * if we faulted "during" the execution of a user specified
 222          * probe handler, invoke just that probe's fault handler
 223          */
 224         if (curr_kprobe && curr_kprobe->fault_handler) {
 225                 if (curr_kprobe->fault_handler(curr_kprobe, regs, trapnr))
 226                         return 1;
 227         }
 228         return 0;
 229 }
 230
 231 static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
 232 {
 233         struct kprobe *kp = curr_kprobe;
 234         if (curr_kprobe && kp->break_handler) {
 235                 if (kp->break_handler(kp, regs)) {
 236                         curr_kprobe = NULL;
 237                         return 1;
 238                 }
 239         }
 240         curr_kprobe = NULL;
 241         return 0;
 242 }
 243
 244 struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
 245 {
 246         struct hlist_node *node;
 247         struct kretprobe_instance *ri;
 248         hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
 249                 return ri;
 250         return NULL;
 251 }
 252
 253 static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
 254                                                               *rp)
 255 {
 256         struct hlist_node *node;
 257         struct kretprobe_instance *ri;
 258         hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
 259                 return ri;
 260         return NULL;
 261 }
 262
 263 void __kprobes add_rp_inst(struct kretprobe_instance *ri)
 264 {
 265         /*
 266          * Remove rp inst off the free list -
 267          * Add it back when probed function returns
 268          */
 269         hlist_del(&ri->uflist);
 270
 271         /* Add rp inst onto table */
 272         INIT_HLIST_NODE(&ri->hlist);
 273         hlist_add_head(&ri->hlist,
 274                         &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);
 275
 276         /* Also add this rp inst to the used list. */
 277         INIT_HLIST_NODE(&ri->uflist);
 278         hlist_add_head(&ri->uflist, &ri->rp->used_instances);
 279 }
 280
 281 void __kprobes recycle_rp_inst(struct kretprobe_instance *ri)
 282 {
 283         /* remove rp inst off the rprobe_inst_table */
 284         hlist_del(&ri->hlist);
 285         if (ri->rp) {
 286                 /* remove rp inst off the used list */
 287                 hlist_del(&ri->uflist);
 288                 /* put rp inst back onto the free list */
 289                 INIT_HLIST_NODE(&ri->uflist);
 290                 hlist_add_head(&ri->uflist, &ri->rp->free_instances);
 291         } else
 292                 /* Unregistering */
 293                 kfree(ri);
 294 }
 295
 296 struct hlist_head __kprobes *kretprobe_inst_table_head(struct task_struct *tsk)
 297 {
 298         return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
 299 }
 300
 301 /*
 302  * This function is called from exit_thread or flush_thread when task tk's
 303  * stack is being recycled so that we can recycle any function-return probe
 304  * instances associated with this task. These left over instances represent
 305  * probed functions that have been called but will never return.
 306  */
 307 void __kprobes kprobe_flush_task(struct task_struct *tk)
 308 {
 309         struct kretprobe_instance *ri;
 310         struct hlist_head *head;
 311         struct hlist_node *node, *tmp;
 312         unsigned long flags = 0;
 313
 314         spin_lock_irqsave(&kprobe_lock, flags);
 315         head = kretprobe_inst_table_head(current);
 316         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 317                 if (ri->task == tk)
 318                         recycle_rp_inst(ri);
 319         }
 320         spin_unlock_irqrestore(&kprobe_lock, flags);
 321 }
 322
 323 /*
 324  * This kprobe pre_handler is registered with every kretprobe. When probe
 325  * hits it will set up the return probe.
 326  */
 327 static int __kprobes pre_handler_kretprobe(struct kprobe *p,
 328                                            struct pt_regs *regs)
 329 {
 330         struct kretprobe *rp = container_of(p, struct kretprobe, kp);
 331
 332         /*TODO: consider to only swap the RA after the last pre_handler fired */
 333         arch_prepare_kretprobe(rp, regs);
 334         return 0;
 335 }
 336
 337 static inline void free_rp_inst(struct kretprobe *rp)
 338 {
 339         struct kretprobe_instance *ri;
 340         while ((ri = get_free_rp_inst(rp)) != NULL) {
 341                 hlist_del(&ri->uflist);
 342                 kfree(ri);
 343         }
 344 }
 345
 346 /*
 347  * Keep all fields in the kprobe consistent
 348  */
 349 static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
 350 {
 351         memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
 352         memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
 353 }
 354
 355 /*
 356 * Add the new probe to old_p->list. Fail if this is the
 357 * second jprobe at the address - two jprobes can't coexist
 358 */
 359 static int __kprobes add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
 360 {
 361         struct kprobe *kp;
 362
 363         if (p->break_handler) {
 364                 list_for_each_entry(kp, &old_p->list, list) {
 365                         if (kp->break_handler)
 366                                 return -EEXIST;
 367                 }
 368                 list_add_tail(&p->list, &old_p->list);
 369         } else
 370                 list_add(&p->list, &old_p->list);
 371         return 0;
 372 }
 373
 374 /*
 375  * Fill in the required fields of the "manager kprobe". Replace the
 376  * earlier kprobe in the hlist with the manager kprobe
 377  */
 378 static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 379 {
 380         copy_kprobe(p, ap);
 381         ap->addr = p->addr;
 382         ap->pre_handler = aggr_pre_handler;
 383         ap->post_handler = aggr_post_handler;
 384         ap->fault_handler = aggr_fault_handler;
 385         ap->break_handler = aggr_break_handler;
 386
 387         INIT_LIST_HEAD(&ap->list);
 388         list_add(&p->list, &ap->list);
 389
 390         INIT_HLIST_NODE(&ap->hlist);
 391         hlist_del(&p->hlist);
 392         hlist_add_head(&ap->hlist,
 393                 &kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
 394 }
 395
 396 /*
 397  * This is the second or subsequent kprobe at the address - handle
 398  * the intricacies
 399  * TODO: Move kcalloc outside the spinlock
 400  */
 401 static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
 402                                           struct kprobe *p)
 403 {
 404         int ret = 0;
 405         struct kprobe *ap;
 406
 407         if (old_p->pre_handler == aggr_pre_handler) {
 408                 copy_kprobe(old_p, p);
 409                 ret = add_new_kprobe(old_p, p);
 410         } else {
 411                 ap = kcalloc(1, sizeof(struct kprobe), GFP_ATOMIC);
 412                 if (!ap)
 413                         return -ENOMEM;
 414                 add_aggr_kprobe(ap, old_p);
 415                 copy_kprobe(ap, p);
 416                 ret = add_new_kprobe(ap, p);
 417         }
 418         return ret;
 419 }
 420
 421 /* kprobe removal house-keeping routines */
 422 static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
 423 {
 424         arch_disarm_kprobe(p);
 425         hlist_del(&p->hlist);
 426         spin_unlock_irqrestore(&kprobe_lock, flags);
 427         arch_remove_kprobe(p);
 428 }
 429
 430 static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
 431                 struct kprobe *p, unsigned long flags)
 432 {
 433         list_del(&p->list);
 434         if (list_empty(&old_p->list)) {
 435                 cleanup_kprobe(old_p, flags);
 436                 kfree(old_p);
 437         } else
 438                 spin_unlock_irqrestore(&kprobe_lock, flags);
 439 }
 440
 441 static int __kprobes in_kprobes_functions(unsigned long addr)
 442 {
 443         if (addr >= (unsigned long)__kprobes_text_start
 444                 && addr < (unsigned long)__kprobes_text_end)
 445                 return -EINVAL;
 446         return 0;
 447 }
 448
 449 int __kprobes register_kprobe(struct kprobe *p)
 450 {
 451         int ret = 0;
 452         unsigned long flags = 0;
 453         struct kprobe *old_p;
 454
 455         if ((ret = in_kprobes_functions((unsigned long) p->addr)) != 0)
 456                 return ret;
 457         if ((ret = arch_prepare_kprobe(p)) != 0)
 458                 goto rm_kprobe;
 459
 460         spin_lock_irqsave(&kprobe_lock, flags);
 461         old_p = get_kprobe(p->addr);
 462         p->nmissed = 0;
 463         if (old_p) {
 464                 ret = register_aggr_kprobe(old_p, p);
 465                 goto out;
 466         }
 467
 468         arch_copy_kprobe(p);
 469         INIT_HLIST_NODE(&p->hlist);
 470         hlist_add_head(&p->hlist,
 471                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 472
 473         arch_arm_kprobe(p);
 474
 475 out:
 476         spin_unlock_irqrestore(&kprobe_lock, flags);
 477 rm_kprobe:
 478         if (ret == -EEXIST)
 479                 arch_remove_kprobe(p);
 480         return ret;
 481 }
 482
 483 void __kprobes unregister_kprobe(struct kprobe *p)
 484 {
 485         unsigned long flags;
 486         struct kprobe *old_p;
 487
 488         spin_lock_irqsave(&kprobe_lock, flags);
 489         old_p = get_kprobe(p->addr);
 490         if (old_p) {
 491                 if (old_p->pre_handler == aggr_pre_handler)
 492                         cleanup_aggr_kprobe(old_p, p, flags);
 493                 else
 494                         cleanup_kprobe(p, flags);
 495         } else
 496                 spin_unlock_irqrestore(&kprobe_lock, flags);
 497 }
 498
 499 static struct notifier_block kprobe_exceptions_nb = {
 500         .notifier_call = kprobe_exceptions_notify,
 501         .priority = 0x7fffffff /* we need to notified first */
 502 };
 503
 504 int __kprobes register_jprobe(struct jprobe *jp)
 505 {
 506         /* Todo: Verify probepoint is a function entry point */
 507         jp->kp.pre_handler = setjmp_pre_handler;
 508         jp->kp.break_handler = longjmp_break_handler;
 509
 510         return register_kprobe(&jp->kp);
 511 }
 512
 513 void __kprobes unregister_jprobe(struct jprobe *jp)
 514 {
 515         unregister_kprobe(&jp->kp);
 516 }
 517
 518 #ifdef ARCH_SUPPORTS_KRETPROBES
 519
 520 int __kprobes register_kretprobe(struct kretprobe *rp)
 521 {
 522         int ret = 0;
 523         struct kretprobe_instance *inst;
 524         int i;
 525
 526         rp->kp.pre_handler = pre_handler_kretprobe;
 527
 528         /* Pre-allocate memory for max kretprobe instances */
 529         if (rp->maxactive <= 0) {
 530 #ifdef CONFIG_PREEMPT
 531                 rp->maxactive = max(10, 2 * NR_CPUS);
 532 #else
 533                 rp->maxactive = NR_CPUS;
 534 #endif
 535         }
 536         INIT_HLIST_HEAD(&rp->used_instances);
 537         INIT_HLIST_HEAD(&rp->free_instances);
 538         for (i = 0; i < rp->maxactive; i++) {
 539                 inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
 540                 if (inst == NULL) {
 541                         free_rp_inst(rp);
 542                         return -ENOMEM;
 543                 }
 544                 INIT_HLIST_NODE(&inst->uflist);
 545                 hlist_add_head(&inst->uflist, &rp->free_instances);
 546         }
 547
 548         rp->nmissed = 0;
 549         /* Establish function entry probe point */
 550         if ((ret = register_kprobe(&rp->kp)) != 0)
 551                 free_rp_inst(rp);
 552         return ret;
 553 }
 554
 555 #else /* ARCH_SUPPORTS_KRETPROBES */
 556
 557 int __kprobes register_kretprobe(struct kretprobe *rp)
 558 {
 559         return -ENOSYS;
 560 }
 561
 562 #endif /* ARCH_SUPPORTS_KRETPROBES */
 563
 564 void __kprobes unregister_kretprobe(struct kretprobe *rp)
 565 {
 566         unsigned long flags;
 567         struct kretprobe_instance *ri;
 568
 569         unregister_kprobe(&rp->kp);
 570         /* No race here */
 571         spin_lock_irqsave(&kprobe_lock, flags);
 572         free_rp_inst(rp);
 573         while ((ri = get_used_rp_inst(rp)) != NULL) {
 574                 ri->rp = NULL;
 575                 hlist_del(&ri->uflist);
 576         }
 577         spin_unlock_irqrestore(&kprobe_lock, flags);
 578 }
 579
 580 static int __init init_kprobes(void)
 581 {
 582         int i, err = 0;
 583
 584         /* FIXME allocate the probe table, currently defined statically */
 585         /* initialize all list heads */
 586         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 587                 INIT_HLIST_HEAD(&kprobe_table[i]);
 588                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
 589         }
 590
 591         err = arch_init_kprobes();
 592         if (!err)
 593                 err = register_die_notifier(&kprobe_exceptions_nb);
 594
 595         return err;
 596 }
 597
 598 __initcall(init_kprobes);
 599
 600 EXPORT_SYMBOL_GPL(register_kprobe);
 601 EXPORT_SYMBOL_GPL(unregister_kprobe);
 602 EXPORT_SYMBOL_GPL(register_jprobe);
 603 EXPORT_SYMBOL_GPL(unregister_jprobe);
 604 EXPORT_SYMBOL_GPL(jprobe_return);
 605 EXPORT_SYMBOL_GPL(register_kretprobe);
 606 EXPORT_SYMBOL_GPL(unregister_kretprobe);
 607