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 <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 static DEFINE_SPINLOCK(kprobe_lock);    /* Protects kprobe_table */
  52 DEFINE_SPINLOCK(kretprobe_lock);        /* Protects kretprobe_inst_table */
  53 static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
  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 /* We have preemption disabled.. so it is safe to use __ versions */
 156 static inline void set_kprobe_instance(struct kprobe *kp)
 157 {
 158         __get_cpu_var(kprobe_instance) = kp;
 159 }
 160
 161 static inline void reset_kprobe_instance(void)
 162 {
 163         __get_cpu_var(kprobe_instance) = NULL;
 164 }
 165
 166 /*
 167  * This routine is called either:
 168  *      - under the kprobe_lock spinlock - during kprobe_[un]register()
 169  *                              OR
 170  *      - with preemption disabled - from arch/xxx/kernel/kprobes.c
 171  */
 172 struct kprobe __kprobes *get_kprobe(void *addr)
 173 {
 174         struct hlist_head *head;
 175         struct hlist_node *node;
 176         struct kprobe *p;
 177
 178         head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
 179         hlist_for_each_entry_rcu(p, node, head, hlist) {
 180                 if (p->addr == addr)
 181                         return p;
 182         }
 183         return NULL;
 184 }
 185
 186 /*
 187  * Aggregate handlers for multiple kprobes support - these handlers
 188  * take care of invoking the individual kprobe handlers on p->list
 189  */
 190 static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
 191 {
 192         struct kprobe *kp;
 193
 194         list_for_each_entry_rcu(kp, &p->list, list) {
 195                 if (kp->pre_handler) {
 196                         set_kprobe_instance(kp);
 197                         if (kp->pre_handler(kp, regs))
 198                                 return 1;
 199                 }
 200                 reset_kprobe_instance();
 201         }
 202         return 0;
 203 }
 204
 205 static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
 206                                         unsigned long flags)
 207 {
 208         struct kprobe *kp;
 209
 210         list_for_each_entry_rcu(kp, &p->list, list) {
 211                 if (kp->post_handler) {
 212                         set_kprobe_instance(kp);
 213                         kp->post_handler(kp, regs, flags);
 214                         reset_kprobe_instance();
 215                 }
 216         }
 217         return;
 218 }
 219
 220 static int __kprobes aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
 221                                         int trapnr)
 222 {
 223         struct kprobe *cur = __get_cpu_var(kprobe_instance);
 224
 225         /*
 226          * if we faulted "during" the execution of a user specified
 227          * probe handler, invoke just that probe's fault handler
 228          */
 229         if (cur && cur->fault_handler) {
 230                 if (cur->fault_handler(cur, regs, trapnr))
 231                         return 1;
 232         }
 233         return 0;
 234 }
 235
 236 static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
 237 {
 238         struct kprobe *cur = __get_cpu_var(kprobe_instance);
 239         int ret = 0;
 240
 241         if (cur && cur->break_handler) {
 242                 if (cur->break_handler(cur, regs))
 243                         ret = 1;
 244         }
 245         reset_kprobe_instance();
 246         return ret;
 247 }
 248
 249 /* Called with kretprobe_lock held */
 250 struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
 251 {
 252         struct hlist_node *node;
 253         struct kretprobe_instance *ri;
 254         hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
 255                 return ri;
 256         return NULL;
 257 }
 258
 259 /* Called with kretprobe_lock held */
 260 static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
 261                                                               *rp)
 262 {
 263         struct hlist_node *node;
 264         struct kretprobe_instance *ri;
 265         hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
 266                 return ri;
 267         return NULL;
 268 }
 269
 270 /* Called with kretprobe_lock held */
 271 void __kprobes add_rp_inst(struct kretprobe_instance *ri)
 272 {
 273         /*
 274          * Remove rp inst off the free list -
 275          * Add it back when probed function returns
 276          */
 277         hlist_del(&ri->uflist);
 278
 279         /* Add rp inst onto table */
 280         INIT_HLIST_NODE(&ri->hlist);
 281         hlist_add_head(&ri->hlist,
 282                         &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);
 283
 284         /* Also add this rp inst to the used list. */
 285         INIT_HLIST_NODE(&ri->uflist);
 286         hlist_add_head(&ri->uflist, &ri->rp->used_instances);
 287 }
 288
 289 /* Called with kretprobe_lock held */
 290 void __kprobes recycle_rp_inst(struct kretprobe_instance *ri)
 291 {
 292         /* remove rp inst off the rprobe_inst_table */
 293         hlist_del(&ri->hlist);
 294         if (ri->rp) {
 295                 /* remove rp inst off the used list */
 296                 hlist_del(&ri->uflist);
 297                 /* put rp inst back onto the free list */
 298                 INIT_HLIST_NODE(&ri->uflist);
 299                 hlist_add_head(&ri->uflist, &ri->rp->free_instances);
 300         } else
 301                 /* Unregistering */
 302                 kfree(ri);
 303 }
 304
 305 struct hlist_head __kprobes *kretprobe_inst_table_head(struct task_struct *tsk)
 306 {
 307         return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
 308 }
 309
 310 /*
 311  * This function is called from exit_thread or flush_thread when task tk's
 312  * stack is being recycled so that we can recycle any function-return probe
 313  * instances associated with this task. These left over instances represent
 314  * probed functions that have been called but will never return.
 315  */
 316 void __kprobes kprobe_flush_task(struct task_struct *tk)
 317 {
 318         struct kretprobe_instance *ri;
 319         struct hlist_head *head;
 320         struct hlist_node *node, *tmp;
 321         unsigned long flags = 0;
 322
 323         spin_lock_irqsave(&kretprobe_lock, flags);
 324         head = kretprobe_inst_table_head(current);
 325         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 326                 if (ri->task == tk)
 327                         recycle_rp_inst(ri);
 328         }
 329         spin_unlock_irqrestore(&kretprobe_lock, flags);
 330 }
 331
 332 /*
 333  * This kprobe pre_handler is registered with every kretprobe. When probe
 334  * hits it will set up the return probe.
 335  */
 336 static int __kprobes pre_handler_kretprobe(struct kprobe *p,
 337                                            struct pt_regs *regs)
 338 {
 339         struct kretprobe *rp = container_of(p, struct kretprobe, kp);
 340         unsigned long flags = 0;
 341
 342         /*TODO: consider to only swap the RA after the last pre_handler fired */
 343         spin_lock_irqsave(&kretprobe_lock, flags);
 344         arch_prepare_kretprobe(rp, regs);
 345         spin_unlock_irqrestore(&kretprobe_lock, flags);
 346         return 0;
 347 }
 348
 349 static inline void free_rp_inst(struct kretprobe *rp)
 350 {
 351         struct kretprobe_instance *ri;
 352         while ((ri = get_free_rp_inst(rp)) != NULL) {
 353                 hlist_del(&ri->uflist);
 354                 kfree(ri);
 355         }
 356 }
 357
 358 /*
 359  * Keep all fields in the kprobe consistent
 360  */
 361 static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
 362 {
 363         memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
 364         memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
 365 }
 366
 367 /*
 368 * Add the new probe to old_p->list. Fail if this is the
 369 * second jprobe at the address - two jprobes can't coexist
 370 */
 371 static int __kprobes add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
 372 {
 373         struct kprobe *kp;
 374
 375         if (p->break_handler) {
 376                 list_for_each_entry_rcu(kp, &old_p->list, list) {
 377                         if (kp->break_handler)
 378                                 return -EEXIST;
 379                 }
 380                 list_add_tail_rcu(&p->list, &old_p->list);
 381         } else
 382                 list_add_rcu(&p->list, &old_p->list);
 383         return 0;
 384 }
 385
 386 /*
 387  * Fill in the required fields of the "manager kprobe". Replace the
 388  * earlier kprobe in the hlist with the manager kprobe
 389  */
 390 static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 391 {
 392         copy_kprobe(p, ap);
 393         ap->addr = p->addr;
 394         ap->pre_handler = aggr_pre_handler;
 395         ap->post_handler = aggr_post_handler;
 396         ap->fault_handler = aggr_fault_handler;
 397         ap->break_handler = aggr_break_handler;
 398
 399         INIT_LIST_HEAD(&ap->list);
 400         list_add_rcu(&p->list, &ap->list);
 401
 402         INIT_HLIST_NODE(&ap->hlist);
 403         hlist_del_rcu(&p->hlist);
 404         hlist_add_head_rcu(&ap->hlist,
 405                 &kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
 406 }
 407
 408 /*
 409  * This is the second or subsequent kprobe at the address - handle
 410  * the intricacies
 411  * TODO: Move kcalloc outside the spin_lock
 412  */
 413 static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
 414                                           struct kprobe *p)
 415 {
 416         int ret = 0;
 417         struct kprobe *ap;
 418
 419         if (old_p->pre_handler == aggr_pre_handler) {
 420                 copy_kprobe(old_p, p);
 421                 ret = add_new_kprobe(old_p, p);
 422         } else {
 423                 ap = kcalloc(1, sizeof(struct kprobe), GFP_ATOMIC);
 424                 if (!ap)
 425                         return -ENOMEM;
 426                 add_aggr_kprobe(ap, old_p);
 427                 copy_kprobe(ap, p);
 428                 ret = add_new_kprobe(ap, p);
 429         }
 430         return ret;
 431 }
 432
 433 /* kprobe removal house-keeping routines */
 434 static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
 435 {
 436         arch_disarm_kprobe(p);
 437         hlist_del_rcu(&p->hlist);
 438         spin_unlock_irqrestore(&kprobe_lock, flags);
 439         arch_remove_kprobe(p);
 440 }
 441
 442 static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
 443                 struct kprobe *p, unsigned long flags)
 444 {
 445         list_del_rcu(&p->list);
 446         if (list_empty(&old_p->list))
 447                 cleanup_kprobe(old_p, flags);
 448         else
 449                 spin_unlock_irqrestore(&kprobe_lock, flags);
 450 }
 451
 452 static int __kprobes in_kprobes_functions(unsigned long addr)
 453 {
 454         if (addr >= (unsigned long)__kprobes_text_start
 455                 && addr < (unsigned long)__kprobes_text_end)
 456                 return -EINVAL;
 457         return 0;
 458 }
 459
 460 int __kprobes register_kprobe(struct kprobe *p)
 461 {
 462         int ret = 0;
 463         unsigned long flags = 0;
 464         struct kprobe *old_p;
 465
 466         if ((ret = in_kprobes_functions((unsigned long) p->addr)) != 0)
 467                 return ret;
 468         if ((ret = arch_prepare_kprobe(p)) != 0)
 469                 goto rm_kprobe;
 470
 471         p->nmissed = 0;
 472         spin_lock_irqsave(&kprobe_lock, flags);
 473         old_p = get_kprobe(p->addr);
 474         if (old_p) {
 475                 ret = register_aggr_kprobe(old_p, p);
 476                 goto out;
 477         }
 478
 479         arch_copy_kprobe(p);
 480         INIT_HLIST_NODE(&p->hlist);
 481         hlist_add_head_rcu(&p->hlist,
 482                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 483
 484         arch_arm_kprobe(p);
 485
 486 out:
 487         spin_unlock_irqrestore(&kprobe_lock, flags);
 488 rm_kprobe:
 489         if (ret == -EEXIST)
 490                 arch_remove_kprobe(p);
 491         return ret;
 492 }
 493
 494 void __kprobes unregister_kprobe(struct kprobe *p)
 495 {
 496         unsigned long flags;
 497         struct kprobe *old_p;
 498
 499         spin_lock_irqsave(&kprobe_lock, flags);
 500         old_p = get_kprobe(p->addr);
 501         if (old_p) {
 502                 /* cleanup_*_kprobe() does the spin_unlock_irqrestore */
 503                 if (old_p->pre_handler == aggr_pre_handler)
 504                         cleanup_aggr_kprobe(old_p, p, flags);
 505                 else
 506                         cleanup_kprobe(p, flags);
 507
 508                 synchronize_sched();
 509                 if (old_p->pre_handler == aggr_pre_handler &&
 510                                 list_empty(&old_p->list))
 511                         kfree(old_p);
 512         } else
 513                 spin_unlock_irqrestore(&kprobe_lock, flags);
 514 }
 515
 516 static struct notifier_block kprobe_exceptions_nb = {
 517         .notifier_call = kprobe_exceptions_notify,
 518         .priority = 0x7fffffff /* we need to notified first */
 519 };
 520
 521 int __kprobes register_jprobe(struct jprobe *jp)
 522 {
 523         /* Todo: Verify probepoint is a function entry point */
 524         jp->kp.pre_handler = setjmp_pre_handler;
 525         jp->kp.break_handler = longjmp_break_handler;
 526
 527         return register_kprobe(&jp->kp);
 528 }
 529
 530 void __kprobes unregister_jprobe(struct jprobe *jp)
 531 {
 532         unregister_kprobe(&jp->kp);
 533 }
 534
 535 #ifdef ARCH_SUPPORTS_KRETPROBES
 536
 537 int __kprobes register_kretprobe(struct kretprobe *rp)
 538 {
 539         int ret = 0;
 540         struct kretprobe_instance *inst;
 541         int i;
 542
 543         rp->kp.pre_handler = pre_handler_kretprobe;
 544
 545         /* Pre-allocate memory for max kretprobe instances */
 546         if (rp->maxactive <= 0) {
 547 #ifdef CONFIG_PREEMPT
 548                 rp->maxactive = max(10, 2 * NR_CPUS);
 549 #else
 550                 rp->maxactive = NR_CPUS;
 551 #endif
 552         }
 553         INIT_HLIST_HEAD(&rp->used_instances);
 554         INIT_HLIST_HEAD(&rp->free_instances);
 555         for (i = 0; i < rp->maxactive; i++) {
 556                 inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
 557                 if (inst == NULL) {
 558                         free_rp_inst(rp);
 559                         return -ENOMEM;
 560                 }
 561                 INIT_HLIST_NODE(&inst->uflist);
 562                 hlist_add_head(&inst->uflist, &rp->free_instances);
 563         }
 564
 565         rp->nmissed = 0;
 566         /* Establish function entry probe point */
 567         if ((ret = register_kprobe(&rp->kp)) != 0)
 568                 free_rp_inst(rp);
 569         return ret;
 570 }
 571
 572 #else /* ARCH_SUPPORTS_KRETPROBES */
 573
 574 int __kprobes register_kretprobe(struct kretprobe *rp)
 575 {
 576         return -ENOSYS;
 577 }
 578
 579 #endif /* ARCH_SUPPORTS_KRETPROBES */
 580
 581 void __kprobes unregister_kretprobe(struct kretprobe *rp)
 582 {
 583         unsigned long flags;
 584         struct kretprobe_instance *ri;
 585
 586         unregister_kprobe(&rp->kp);
 587         /* No race here */
 588         spin_lock_irqsave(&kretprobe_lock, flags);
 589         free_rp_inst(rp);
 590         while ((ri = get_used_rp_inst(rp)) != NULL) {
 591                 ri->rp = NULL;
 592                 hlist_del(&ri->uflist);
 593         }
 594         spin_unlock_irqrestore(&kretprobe_lock, flags);
 595 }
 596
 597 static int __init init_kprobes(void)
 598 {
 599         int i, err = 0;
 600
 601         /* FIXME allocate the probe table, currently defined statically */
 602         /* initialize all list heads */
 603         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 604                 INIT_HLIST_HEAD(&kprobe_table[i]);
 605                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
 606         }
 607
 608         err = arch_init_kprobes();
 609         if (!err)
 610                 err = register_die_notifier(&kprobe_exceptions_nb);
 611
 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