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/cacheflush.h>
  41 #include <asm/errno.h>
  42 #include <asm/kdebug.h>
  43
  44 #define KPROBE_HASH_BITS 6
  45 #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
  46
  47 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
  48 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
  49
  50 unsigned int kprobe_cpu = NR_CPUS;
  51 static DEFINE_SPINLOCK(kprobe_lock);
  52 static struct kprobe *curr_kprobe;
  53
  54 /*
  55  * kprobe->ainsn.insn points to the copy of the instruction to be
  56  * single-stepped. x86_64, POWER4 and above have no-exec support and
  57  * stepping on the instruction on a vmalloced/kmalloced/data page
  58  * is a recipe for disaster
  59  */
  60 #define INSNS_PER_PAGE  (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
  61
  62 struct kprobe_insn_page {
  63         struct hlist_node hlist;
  64         kprobe_opcode_t *insns;         /* Page of instruction slots */
  65         char slot_used[INSNS_PER_PAGE];
  66         int nused;
  67 };
  68
  69 static struct hlist_head kprobe_insn_pages;
  70
  71 /**
  72  * get_insn_slot() - Find a slot on an executable page for an instruction.
  73  * We allocate an executable page if there's no room on existing ones.
  74  */
  75 kprobe_opcode_t *get_insn_slot(void)
  76 {
  77         struct kprobe_insn_page *kip;
  78         struct hlist_node *pos;
  79
  80         hlist_for_each(pos, &kprobe_insn_pages) {
  81                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
  82                 if (kip->nused < INSNS_PER_PAGE) {
  83                         int i;
  84                         for (i = 0; i < INSNS_PER_PAGE; i++) {
  85                                 if (!kip->slot_used[i]) {
  86                                         kip->slot_used[i] = 1;
  87                                         kip->nused++;
  88                                         return kip->insns + (i * MAX_INSN_SIZE);
  89                                 }
  90                         }
  91                         /* Surprise!  No unused slots.  Fix kip->nused. */
  92                         kip->nused = INSNS_PER_PAGE;
  93                 }
  94         }
  95
  96         /* All out of space.  Need to allocate a new page. Use slot 0.*/
  97         kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
  98         if (!kip) {
  99                 return NULL;
 100         }
 101
 102         /*
 103          * Use module_alloc so this page is within +/- 2GB of where the
 104          * kernel image and loaded module images reside. This is required
 105          * so x86_64 can correctly handle the %rip-relative fixups.
 106          */
 107         kip->insns = module_alloc(PAGE_SIZE);
 108         if (!kip->insns) {
 109                 kfree(kip);
 110                 return NULL;
 111         }
 112         INIT_HLIST_NODE(&kip->hlist);
 113         hlist_add_head(&kip->hlist, &kprobe_insn_pages);
 114         memset(kip->slot_used, 0, INSNS_PER_PAGE);
 115         kip->slot_used[0] = 1;
 116         kip->nused = 1;
 117         return kip->insns;
 118 }
 119
 120 void free_insn_slot(kprobe_opcode_t *slot)
 121 {
 122         struct kprobe_insn_page *kip;
 123         struct hlist_node *pos;
 124
 125         hlist_for_each(pos, &kprobe_insn_pages) {
 126                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
 127                 if (kip->insns <= slot &&
 128                     slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
 129                         int i = (slot - kip->insns) / MAX_INSN_SIZE;
 130                         kip->slot_used[i] = 0;
 131                         kip->nused--;
 132                         if (kip->nused == 0) {
 133                                 /*
 134                                  * Page is no longer in use.  Free it unless
 135                                  * it's the last one.  We keep the last one
 136                                  * so as not to have to set it up again the
 137                                  * next time somebody inserts a probe.
 138                                  */
 139                                 hlist_del(&kip->hlist);
 140                                 if (hlist_empty(&kprobe_insn_pages)) {
 141                                         INIT_HLIST_NODE(&kip->hlist);
 142                                         hlist_add_head(&kip->hlist,
 143                                                 &kprobe_insn_pages);
 144                                 } else {
 145                                         module_free(NULL, kip->insns);
 146                                         kfree(kip);
 147                                 }
 148                         }
 149                         return;
 150                 }
 151         }
 152 }
 153
 154 /* Locks kprobe: irqs must be disabled */
 155 void lock_kprobes(void)
 156 {
 157         spin_lock(&kprobe_lock);
 158         kprobe_cpu = smp_processor_id();
 159 }
 160
 161 void unlock_kprobes(void)
 162 {
 163         kprobe_cpu = NR_CPUS;
 164         spin_unlock(&kprobe_lock);
 165 }
 166
 167 /* You have to be holding the kprobe_lock */
 168 struct kprobe *get_kprobe(void *addr)
 169 {
 170         struct hlist_head *head;
 171         struct hlist_node *node;
 172
 173         head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
 174         hlist_for_each(node, head) {
 175                 struct kprobe *p = hlist_entry(node, struct kprobe, hlist);
 176                 if (p->addr == addr)
 177                         return p;
 178         }
 179         return NULL;
 180 }
 181
 182 /*
 183  * Aggregate handlers for multiple kprobes support - these handlers
 184  * take care of invoking the individual kprobe handlers on p->list
 185  */
 186 static int aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
 187 {
 188         struct kprobe *kp;
 189
 190         list_for_each_entry(kp, &p->list, list) {
 191                 if (kp->pre_handler) {
 192                         curr_kprobe = kp;
 193                         if (kp->pre_handler(kp, regs))
 194                                 return 1;
 195                 }
 196                 curr_kprobe = NULL;
 197         }
 198         return 0;
 199 }
 200
 201 static void aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
 202                               unsigned long flags)
 203 {
 204         struct kprobe *kp;
 205
 206         list_for_each_entry(kp, &p->list, list) {
 207                 if (kp->post_handler) {
 208                         curr_kprobe = kp;
 209                         kp->post_handler(kp, regs, flags);
 210                         curr_kprobe = NULL;
 211                 }
 212         }
 213         return;
 214 }
 215
 216 static int aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
 217                               int trapnr)
 218 {
 219         /*
 220          * if we faulted "during" the execution of a user specified
 221          * probe handler, invoke just that probe's fault handler
 222          */
 223         if (curr_kprobe && curr_kprobe->fault_handler) {
 224                 if (curr_kprobe->fault_handler(curr_kprobe, regs, trapnr))
 225                         return 1;
 226         }
 227         return 0;
 228 }
 229
 230 static int aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
 231 {
 232         struct kprobe *kp = curr_kprobe;
 233         if (curr_kprobe && kp->break_handler) {
 234                 if (kp->break_handler(kp, regs)) {
 235                         curr_kprobe = NULL;
 236                         return 1;
 237                 }
 238         }
 239         curr_kprobe = NULL;
 240         return 0;
 241 }
 242
 243 struct kprobe trampoline_p = {
 244                 .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 245                 .pre_handler = trampoline_probe_handler,
 246                 .post_handler = trampoline_post_handler
 247 };
 248
 249 struct kretprobe_instance *get_free_rp_inst(struct kretprobe *rp)
 250 {
 251         struct hlist_node *node;
 252         struct kretprobe_instance *ri;
 253         hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
 254                 return ri;
 255         return NULL;
 256 }
 257
 258 static struct kretprobe_instance *get_used_rp_inst(struct kretprobe *rp)
 259 {
 260         struct hlist_node *node;
 261         struct kretprobe_instance *ri;
 262         hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
 263                 return ri;
 264         return NULL;
 265 }
 266
 267 struct kretprobe_instance *get_rp_inst(void *sara)
 268 {
 269         struct hlist_head *head;
 270         struct hlist_node *node;
 271         struct task_struct *tsk;
 272         struct kretprobe_instance *ri;
 273
 274         tsk = arch_get_kprobe_task(sara);
 275         head = &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
 276         hlist_for_each_entry(ri, node, head, hlist) {
 277                 if (ri->stack_addr == sara)
 278                         return ri;
 279         }
 280         return NULL;
 281 }
 282
 283 void add_rp_inst(struct kretprobe_instance *ri)
 284 {
 285         struct task_struct *tsk;
 286         /*
 287          * Remove rp inst off the free list -
 288          * Add it back when probed function returns
 289          */
 290         hlist_del(&ri->uflist);
 291         tsk = arch_get_kprobe_task(ri->stack_addr);
 292         /* Add rp inst onto table */
 293         INIT_HLIST_NODE(&ri->hlist);
 294         hlist_add_head(&ri->hlist,
 295                         &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)]);
 296
 297         /* Also add this rp inst to the used list. */
 298         INIT_HLIST_NODE(&ri->uflist);
 299         hlist_add_head(&ri->uflist, &ri->rp->used_instances);
 300 }
 301
 302 void recycle_rp_inst(struct kretprobe_instance *ri)
 303 {
 304         /* remove rp inst off the rprobe_inst_table */
 305         hlist_del(&ri->hlist);
 306         if (ri->rp) {
 307                 /* remove rp inst off the used list */
 308                 hlist_del(&ri->uflist);
 309                 /* put rp inst back onto the free list */
 310                 INIT_HLIST_NODE(&ri->uflist);
 311                 hlist_add_head(&ri->uflist, &ri->rp->free_instances);
 312         } else
 313                 /* Unregistering */
 314                 kfree(ri);
 315 }
 316
 317 struct hlist_head * kretprobe_inst_table_head(struct task_struct *tsk)
 318 {
 319         return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
 320 }
 321
 322 struct kretprobe_instance *get_rp_inst_tsk(struct task_struct *tk)
 323 {
 324         struct task_struct *tsk;
 325         struct hlist_head *head;
 326         struct hlist_node *node;
 327         struct kretprobe_instance *ri;
 328
 329         head = &kretprobe_inst_table[hash_ptr(tk, KPROBE_HASH_BITS)];
 330
 331         hlist_for_each_entry(ri, node, head, hlist) {
 332                 tsk = arch_get_kprobe_task(ri->stack_addr);
 333                 if (tsk == tk)
 334                         return ri;
 335         }
 336         return NULL;
 337 }
 338
 339 /*
 340  * This function is called from do_exit or do_execv when task tk's stack is
 341  * about to be recycled. Recycle any function-return probe instances
 342  * associated with this task. These represent probed functions that have
 343  * been called but may never return.
 344  */
 345 void kprobe_flush_task(struct task_struct *tk)
 346 {
 347         unsigned long flags = 0;
 348         spin_lock_irqsave(&kprobe_lock, flags);
 349         arch_kprobe_flush_task(tk);
 350         spin_unlock_irqrestore(&kprobe_lock, flags);
 351 }
 352
 353 /*
 354  * This kprobe pre_handler is registered with every kretprobe. When probe
 355  * hits it will set up the return probe.
 356  */
 357 static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
 358 {
 359         struct kretprobe *rp = container_of(p, struct kretprobe, kp);
 360
 361         /*TODO: consider to only swap the RA after the last pre_handler fired */
 362         arch_prepare_kretprobe(rp, regs);
 363         return 0;
 364 }
 365
 366 static inline void free_rp_inst(struct kretprobe *rp)
 367 {
 368         struct kretprobe_instance *ri;
 369         while ((ri = get_free_rp_inst(rp)) != NULL) {
 370                 hlist_del(&ri->uflist);
 371                 kfree(ri);
 372         }
 373 }
 374
 375 /*
 376  * Keep all fields in the kprobe consistent
 377  */
 378 static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
 379 {
 380         memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
 381         memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
 382 }
 383
 384 /*
 385 * Add the new probe to old_p->list. Fail if this is the
 386 * second jprobe at the address - two jprobes can't coexist
 387 */
 388 static int add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
 389 {
 390         struct kprobe *kp;
 391
 392         if (p->break_handler) {
 393                 list_for_each_entry(kp, &old_p->list, list) {
 394                         if (kp->break_handler)
 395                                 return -EEXIST;
 396                 }
 397                 list_add_tail(&p->list, &old_p->list);
 398         } else
 399                 list_add(&p->list, &old_p->list);
 400         return 0;
 401 }
 402
 403 /*
 404  * Fill in the required fields of the "manager kprobe". Replace the
 405  * earlier kprobe in the hlist with the manager kprobe
 406  */
 407 static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 408 {
 409         copy_kprobe(p, ap);
 410         ap->addr = p->addr;
 411         ap->pre_handler = aggr_pre_handler;
 412         ap->post_handler = aggr_post_handler;
 413         ap->fault_handler = aggr_fault_handler;
 414         ap->break_handler = aggr_break_handler;
 415
 416         INIT_LIST_HEAD(&ap->list);
 417         list_add(&p->list, &ap->list);
 418
 419         INIT_HLIST_NODE(&ap->hlist);
 420         hlist_del(&p->hlist);
 421         hlist_add_head(&ap->hlist,
 422                 &kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
 423 }
 424
 425 /*
 426  * This is the second or subsequent kprobe at the address - handle
 427  * the intricacies
 428  * TODO: Move kcalloc outside the spinlock
 429  */
 430 static int register_aggr_kprobe(struct kprobe *old_p, struct kprobe *p)
 431 {
 432         int ret = 0;
 433         struct kprobe *ap;
 434
 435         if (old_p->pre_handler == aggr_pre_handler) {
 436                 copy_kprobe(old_p, p);
 437                 ret = add_new_kprobe(old_p, p);
 438         } else {
 439                 ap = kcalloc(1, sizeof(struct kprobe), GFP_ATOMIC);
 440                 if (!ap)
 441                         return -ENOMEM;
 442                 add_aggr_kprobe(ap, old_p);
 443                 copy_kprobe(ap, p);
 444                 ret = add_new_kprobe(ap, p);
 445         }
 446         return ret;
 447 }
 448
 449 /* kprobe removal house-keeping routines */
 450 static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
 451 {
 452         arch_disarm_kprobe(p);
 453         hlist_del(&p->hlist);
 454         spin_unlock_irqrestore(&kprobe_lock, flags);
 455         arch_remove_kprobe(p);
 456 }
 457
 458 static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
 459                 struct kprobe *p, unsigned long flags)
 460 {
 461         list_del(&p->list);
 462         if (list_empty(&old_p->list)) {
 463                 cleanup_kprobe(old_p, flags);
 464                 kfree(old_p);
 465         } else
 466                 spin_unlock_irqrestore(&kprobe_lock, flags);
 467 }
 468
 469 int register_kprobe(struct kprobe *p)
 470 {
 471         int ret = 0;
 472         unsigned long flags = 0;
 473         struct kprobe *old_p;
 474
 475         if ((ret = arch_prepare_kprobe(p)) != 0) {
 476                 goto rm_kprobe;
 477         }
 478         spin_lock_irqsave(&kprobe_lock, flags);
 479         old_p = get_kprobe(p->addr);
 480         p->nmissed = 0;
 481         if (old_p) {
 482                 ret = register_aggr_kprobe(old_p, p);
 483                 goto out;
 484         }
 485
 486         arch_copy_kprobe(p);
 487         INIT_HLIST_NODE(&p->hlist);
 488         hlist_add_head(&p->hlist,
 489                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 490
 491         arch_arm_kprobe(p);
 492
 493 out:
 494         spin_unlock_irqrestore(&kprobe_lock, flags);
 495 rm_kprobe:
 496         if (ret == -EEXIST)
 497                 arch_remove_kprobe(p);
 498         return ret;
 499 }
 500
 501 void unregister_kprobe(struct kprobe *p)
 502 {
 503         unsigned long flags;
 504         struct kprobe *old_p;
 505
 506         spin_lock_irqsave(&kprobe_lock, flags);
 507         old_p = get_kprobe(p->addr);
 508         if (old_p) {
 509                 if (old_p->pre_handler == aggr_pre_handler)
 510                         cleanup_aggr_kprobe(old_p, p, flags);
 511                 else
 512                         cleanup_kprobe(p, flags);
 513         } else
 514                 spin_unlock_irqrestore(&kprobe_lock, flags);
 515 }
 516
 517 static struct notifier_block kprobe_exceptions_nb = {
 518         .notifier_call = kprobe_exceptions_notify,
 519         .priority = 0x7fffffff /* we need to notified first */
 520 };
 521
 522 int register_jprobe(struct jprobe *jp)
 523 {
 524         /* Todo: Verify probepoint is a function entry point */
 525         jp->kp.pre_handler = setjmp_pre_handler;
 526         jp->kp.break_handler = longjmp_break_handler;
 527
 528         return register_kprobe(&jp->kp);
 529 }
 530
 531 void unregister_jprobe(struct jprobe *jp)
 532 {
 533         unregister_kprobe(&jp->kp);
 534 }
 535
 536 #ifdef ARCH_SUPPORTS_KRETPROBES
 537
 538 int register_kretprobe(struct kretprobe *rp)
 539 {
 540         int ret = 0;
 541         struct kretprobe_instance *inst;
 542         int i;
 543
 544         rp->kp.pre_handler = pre_handler_kretprobe;
 545
 546         /* Pre-allocate memory for max kretprobe instances */
 547         if (rp->maxactive <= 0) {
 548 #ifdef CONFIG_PREEMPT
 549                 rp->maxactive = max(10, 2 * NR_CPUS);
 550 #else
 551                 rp->maxactive = NR_CPUS;
 552 #endif
 553         }
 554         INIT_HLIST_HEAD(&rp->used_instances);
 555         INIT_HLIST_HEAD(&rp->free_instances);
 556         for (i = 0; i < rp->maxactive; i++) {
 557                 inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
 558                 if (inst == NULL) {
 559                         free_rp_inst(rp);
 560                         return -ENOMEM;
 561                 }
 562                 INIT_HLIST_NODE(&inst->uflist);
 563                 hlist_add_head(&inst->uflist, &rp->free_instances);
 564         }
 565
 566         rp->nmissed = 0;
 567         /* Establish function entry probe point */
 568         if ((ret = register_kprobe(&rp->kp)) != 0)
 569                 free_rp_inst(rp);
 570         return ret;
 571 }
 572
 573 #else /* ARCH_SUPPORTS_KRETPROBES */
 574
 575 int register_kretprobe(struct kretprobe *rp)
 576 {
 577         return -ENOSYS;
 578 }
 579
 580 #endif /* ARCH_SUPPORTS_KRETPROBES */
 581
 582 void unregister_kretprobe(struct kretprobe *rp)
 583 {
 584         unsigned long flags;
 585         struct kretprobe_instance *ri;
 586
 587         unregister_kprobe(&rp->kp);
 588         /* No race here */
 589         spin_lock_irqsave(&kprobe_lock, flags);
 590         free_rp_inst(rp);
 591         while ((ri = get_used_rp_inst(rp)) != NULL) {
 592                 ri->rp = NULL;
 593                 hlist_del(&ri->uflist);
 594         }
 595         spin_unlock_irqrestore(&kprobe_lock, flags);
 596 }
 597
 598 static int __init init_kprobes(void)
 599 {
 600         int i, err = 0;
 601
 602         /* FIXME allocate the probe table, currently defined statically */
 603         /* initialize all list heads */
 604         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 605                 INIT_HLIST_HEAD(&kprobe_table[i]);
 606                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
 607         }
 608
 609         err = register_die_notifier(&kprobe_exceptions_nb);
 610         /* Register the trampoline probe for return probe */
 611         register_kprobe(&trampoline_p);
 612         return err;
 613 }
 614
 615 __initcall(init_kprobes);
 616
 617 EXPORT_SYMBOL_GPL(register_kprobe);
 618 EXPORT_SYMBOL_GPL(unregister_kprobe);
 619 EXPORT_SYMBOL_GPL(register_jprobe);
 620 EXPORT_SYMBOL_GPL(unregister_jprobe);
 621 EXPORT_SYMBOL_GPL(jprobe_return);
 622 EXPORT_SYMBOL_GPL(register_kretprobe);
 623 EXPORT_SYMBOL_GPL(unregister_kretprobe);
 624