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 <asm/cacheflush.h>
  40 #include <asm/errno.h>
  41 #include <asm/kdebug.h>
  42
  43 #define KPROBE_HASH_BITS 6
  44 #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
  45
  46 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
  47 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
  48
  49 unsigned int kprobe_cpu = NR_CPUS;
  50 static DEFINE_SPINLOCK(kprobe_lock);
  51 static struct kprobe *curr_kprobe;
  52
  53 /* Locks kprobe: irqs must be disabled */
  54 void lock_kprobes(void)
  55 {
  56         spin_lock(&kprobe_lock);
  57         kprobe_cpu = smp_processor_id();
  58 }
  59
  60 void unlock_kprobes(void)
  61 {
  62         kprobe_cpu = NR_CPUS;
  63         spin_unlock(&kprobe_lock);
  64 }
  65
  66 /* You have to be holding the kprobe_lock */
  67 struct kprobe *get_kprobe(void *addr)
  68 {
  69         struct hlist_head *head;
  70         struct hlist_node *node;
  71
  72         head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
  73         hlist_for_each(node, head) {
  74                 struct kprobe *p = hlist_entry(node, struct kprobe, hlist);
  75                 if (p->addr == addr)
  76                         return p;
  77         }
  78         return NULL;
  79 }
  80
  81 /*
  82  * Aggregate handlers for multiple kprobes support - these handlers
  83  * take care of invoking the individual kprobe handlers on p->list
  84  */
  85 static int aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
  86 {
  87         struct kprobe *kp;
  88
  89         list_for_each_entry(kp, &p->list, list) {
  90                 if (kp->pre_handler) {
  91                         curr_kprobe = kp;
  92                         kp->pre_handler(kp, regs);
  93                         curr_kprobe = NULL;
  94                 }
  95         }
  96         return 0;
  97 }
  98
  99 static void aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
 100                               unsigned long flags)
 101 {
 102         struct kprobe *kp;
 103
 104         list_for_each_entry(kp, &p->list, list) {
 105                 if (kp->post_handler) {
 106                         curr_kprobe = kp;
 107                         kp->post_handler(kp, regs, flags);
 108                         curr_kprobe = NULL;
 109                 }
 110         }
 111         return;
 112 }
 113
 114 static int aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
 115                               int trapnr)
 116 {
 117         /*
 118          * if we faulted "during" the execution of a user specified
 119          * probe handler, invoke just that probe's fault handler
 120          */
 121         if (curr_kprobe && curr_kprobe->fault_handler) {
 122                 if (curr_kprobe->fault_handler(curr_kprobe, regs, trapnr))
 123                         return 1;
 124         }
 125         return 0;
 126 }
 127
 128 struct kprobe trampoline_p = {
 129                 .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 130                 .pre_handler = trampoline_probe_handler,
 131                 .post_handler = trampoline_post_handler
 132 };
 133
 134 struct kretprobe_instance *get_free_rp_inst(struct kretprobe *rp)
 135 {
 136         struct hlist_node *node;
 137         struct kretprobe_instance *ri;
 138         hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
 139                 return ri;
 140         return NULL;
 141 }
 142
 143 static struct kretprobe_instance *get_used_rp_inst(struct kretprobe *rp)
 144 {
 145         struct hlist_node *node;
 146         struct kretprobe_instance *ri;
 147         hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
 148                 return ri;
 149         return NULL;
 150 }
 151
 152 struct kretprobe_instance *get_rp_inst(void *sara)
 153 {
 154         struct hlist_head *head;
 155         struct hlist_node *node;
 156         struct task_struct *tsk;
 157         struct kretprobe_instance *ri;
 158
 159         tsk = arch_get_kprobe_task(sara);
 160         head = &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
 161         hlist_for_each_entry(ri, node, head, hlist) {
 162                 if (ri->stack_addr == sara)
 163                         return ri;
 164         }
 165         return NULL;
 166 }
 167
 168 void add_rp_inst(struct kretprobe_instance *ri)
 169 {
 170         struct task_struct *tsk;
 171         /*
 172          * Remove rp inst off the free list -
 173          * Add it back when probed function returns
 174          */
 175         hlist_del(&ri->uflist);
 176         tsk = arch_get_kprobe_task(ri->stack_addr);
 177         /* Add rp inst onto table */
 178         INIT_HLIST_NODE(&ri->hlist);
 179         hlist_add_head(&ri->hlist,
 180                         &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)]);
 181
 182         /* Also add this rp inst to the used list. */
 183         INIT_HLIST_NODE(&ri->uflist);
 184         hlist_add_head(&ri->uflist, &ri->rp->used_instances);
 185 }
 186
 187 void recycle_rp_inst(struct kretprobe_instance *ri)
 188 {
 189         /* remove rp inst off the rprobe_inst_table */
 190         hlist_del(&ri->hlist);
 191         if (ri->rp) {
 192                 /* remove rp inst off the used list */
 193                 hlist_del(&ri->uflist);
 194                 /* put rp inst back onto the free list */
 195                 INIT_HLIST_NODE(&ri->uflist);
 196                 hlist_add_head(&ri->uflist, &ri->rp->free_instances);
 197         } else
 198                 /* Unregistering */
 199                 kfree(ri);
 200 }
 201
 202 struct hlist_head * kretprobe_inst_table_head(struct task_struct *tsk)
 203 {
 204         return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
 205 }
 206
 207 struct kretprobe_instance *get_rp_inst_tsk(struct task_struct *tk)
 208 {
 209         struct task_struct *tsk;
 210         struct hlist_head *head;
 211         struct hlist_node *node;
 212         struct kretprobe_instance *ri;
 213
 214         head = &kretprobe_inst_table[hash_ptr(tk, KPROBE_HASH_BITS)];
 215
 216         hlist_for_each_entry(ri, node, head, hlist) {
 217                 tsk = arch_get_kprobe_task(ri->stack_addr);
 218                 if (tsk == tk)
 219                         return ri;
 220         }
 221         return NULL;
 222 }
 223
 224 /*
 225  * This function is called from do_exit or do_execv when task tk's stack is
 226  * about to be recycled. Recycle any function-return probe instances
 227  * associated with this task. These represent probed functions that have
 228  * been called but may never return.
 229  */
 230 void kprobe_flush_task(struct task_struct *tk)
 231 {
 232         unsigned long flags = 0;
 233         spin_lock_irqsave(&kprobe_lock, flags);
 234         arch_kprobe_flush_task(tk);
 235         spin_unlock_irqrestore(&kprobe_lock, flags);
 236 }
 237
 238 /*
 239  * This kprobe pre_handler is registered with every kretprobe. When probe
 240  * hits it will set up the return probe.
 241  */
 242 static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
 243 {
 244         struct kretprobe *rp = container_of(p, struct kretprobe, kp);
 245
 246         /*TODO: consider to only swap the RA after the last pre_handler fired */
 247         arch_prepare_kretprobe(rp, regs);
 248         return 0;
 249 }
 250
 251 static inline void free_rp_inst(struct kretprobe *rp)
 252 {
 253         struct kretprobe_instance *ri;
 254         while ((ri = get_free_rp_inst(rp)) != NULL) {
 255                 hlist_del(&ri->uflist);
 256                 kfree(ri);
 257         }
 258 }
 259
 260 /*
 261  * Fill in the required fields of the "manager kprobe". Replace the
 262  * earlier kprobe in the hlist with the manager kprobe
 263  */
 264 static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 265 {
 266         ap->addr = p->addr;
 267         memcpy(&ap->opcode, &p->opcode, sizeof(kprobe_opcode_t));
 268         memcpy(&ap->ainsn, &p->ainsn, sizeof(struct arch_specific_insn));
 269
 270         ap->pre_handler = aggr_pre_handler;
 271         ap->post_handler = aggr_post_handler;
 272         ap->fault_handler = aggr_fault_handler;
 273
 274         INIT_LIST_HEAD(&ap->list);
 275         list_add(&p->list, &ap->list);
 276
 277         INIT_HLIST_NODE(&ap->hlist);
 278         hlist_del(&p->hlist);
 279         hlist_add_head(&ap->hlist,
 280                 &kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
 281 }
 282
 283 /*
 284  * This is the second or subsequent kprobe at the address - handle
 285  * the intricacies
 286  * TODO: Move kcalloc outside the spinlock
 287  */
 288 static int register_aggr_kprobe(struct kprobe *old_p, struct kprobe *p)
 289 {
 290         int ret = 0;
 291         struct kprobe *ap;
 292
 293         if (old_p->break_handler || p->break_handler) {
 294                 ret = -EEXIST;  /* kprobe and jprobe can't (yet) coexist */
 295         } else if (old_p->pre_handler == aggr_pre_handler) {
 296                 list_add(&p->list, &old_p->list);
 297         } else {
 298                 ap = kcalloc(1, sizeof(struct kprobe), GFP_ATOMIC);
 299                 if (!ap)
 300                         return -ENOMEM;
 301                 add_aggr_kprobe(ap, old_p);
 302                 list_add(&p->list, &ap->list);
 303         }
 304         return ret;
 305 }
 306
 307 /* kprobe removal house-keeping routines */
 308 static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
 309 {
 310         arch_disarm_kprobe(p);
 311         hlist_del(&p->hlist);
 312         spin_unlock_irqrestore(&kprobe_lock, flags);
 313         arch_remove_kprobe(p);
 314 }
 315
 316 static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
 317                 struct kprobe *p, unsigned long flags)
 318 {
 319         list_del(&p->list);
 320         if (list_empty(&old_p->list)) {
 321                 cleanup_kprobe(old_p, flags);
 322                 kfree(old_p);
 323         } else
 324                 spin_unlock_irqrestore(&kprobe_lock, flags);
 325 }
 326
 327 int register_kprobe(struct kprobe *p)
 328 {
 329         int ret = 0;
 330         unsigned long flags = 0;
 331         struct kprobe *old_p;
 332
 333         if ((ret = arch_prepare_kprobe(p)) != 0) {
 334                 goto rm_kprobe;
 335         }
 336         spin_lock_irqsave(&kprobe_lock, flags);
 337         old_p = get_kprobe(p->addr);
 338         p->nmissed = 0;
 339         if (old_p) {
 340                 ret = register_aggr_kprobe(old_p, p);
 341                 goto out;
 342         }
 343
 344         arch_copy_kprobe(p);
 345         INIT_HLIST_NODE(&p->hlist);
 346         hlist_add_head(&p->hlist,
 347                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 348
 349         arch_arm_kprobe(p);
 350
 351 out:
 352         spin_unlock_irqrestore(&kprobe_lock, flags);
 353 rm_kprobe:
 354         if (ret == -EEXIST)
 355                 arch_remove_kprobe(p);
 356         return ret;
 357 }
 358
 359 void unregister_kprobe(struct kprobe *p)
 360 {
 361         unsigned long flags;
 362         struct kprobe *old_p;
 363
 364         spin_lock_irqsave(&kprobe_lock, flags);
 365         old_p = get_kprobe(p->addr);
 366         if (old_p) {
 367                 if (old_p->pre_handler == aggr_pre_handler)
 368                         cleanup_aggr_kprobe(old_p, p, flags);
 369                 else
 370                         cleanup_kprobe(p, flags);
 371         } else
 372                 spin_unlock_irqrestore(&kprobe_lock, flags);
 373 }
 374
 375 static struct notifier_block kprobe_exceptions_nb = {
 376         .notifier_call = kprobe_exceptions_notify,
 377         .priority = 0x7fffffff /* we need to notified first */
 378 };
 379
 380 int register_jprobe(struct jprobe *jp)
 381 {
 382         /* Todo: Verify probepoint is a function entry point */
 383         jp->kp.pre_handler = setjmp_pre_handler;
 384         jp->kp.break_handler = longjmp_break_handler;
 385
 386         return register_kprobe(&jp->kp);
 387 }
 388
 389 void unregister_jprobe(struct jprobe *jp)
 390 {
 391         unregister_kprobe(&jp->kp);
 392 }
 393
 394 #ifdef ARCH_SUPPORTS_KRETPROBES
 395
 396 int register_kretprobe(struct kretprobe *rp)
 397 {
 398         int ret = 0;
 399         struct kretprobe_instance *inst;
 400         int i;
 401
 402         rp->kp.pre_handler = pre_handler_kretprobe;
 403
 404         /* Pre-allocate memory for max kretprobe instances */
 405         if (rp->maxactive <= 0) {
 406 #ifdef CONFIG_PREEMPT
 407                 rp->maxactive = max(10, 2 * NR_CPUS);
 408 #else
 409                 rp->maxactive = NR_CPUS;
 410 #endif
 411         }
 412         INIT_HLIST_HEAD(&rp->used_instances);
 413         INIT_HLIST_HEAD(&rp->free_instances);
 414         for (i = 0; i < rp->maxactive; i++) {
 415                 inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
 416                 if (inst == NULL) {
 417                         free_rp_inst(rp);
 418                         return -ENOMEM;
 419                 }
 420                 INIT_HLIST_NODE(&inst->uflist);
 421                 hlist_add_head(&inst->uflist, &rp->free_instances);
 422         }
 423
 424         rp->nmissed = 0;
 425         /* Establish function entry probe point */
 426         if ((ret = register_kprobe(&rp->kp)) != 0)
 427                 free_rp_inst(rp);
 428         return ret;
 429 }
 430
 431 #else /* ARCH_SUPPORTS_KRETPROBES */
 432
 433 int register_kretprobe(struct kretprobe *rp)
 434 {
 435         return -ENOSYS;
 436 }
 437
 438 #endif /* ARCH_SUPPORTS_KRETPROBES */
 439
 440 void unregister_kretprobe(struct kretprobe *rp)
 441 {
 442         unsigned long flags;
 443         struct kretprobe_instance *ri;
 444
 445         unregister_kprobe(&rp->kp);
 446         /* No race here */
 447         spin_lock_irqsave(&kprobe_lock, flags);
 448         free_rp_inst(rp);
 449         while ((ri = get_used_rp_inst(rp)) != NULL) {
 450                 ri->rp = NULL;
 451                 hlist_del(&ri->uflist);
 452         }
 453         spin_unlock_irqrestore(&kprobe_lock, flags);
 454 }
 455
 456 static int __init init_kprobes(void)
 457 {
 458         int i, err = 0;
 459
 460         /* FIXME allocate the probe table, currently defined statically */
 461         /* initialize all list heads */
 462         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 463                 INIT_HLIST_HEAD(&kprobe_table[i]);
 464                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
 465         }
 466
 467         err = register_die_notifier(&kprobe_exceptions_nb);
 468         /* Register the trampoline probe for return probe */
 469         register_kprobe(&trampoline_p);
 470         return err;
 471 }
 472
 473 __initcall(init_kprobes);
 474
 475 EXPORT_SYMBOL_GPL(register_kprobe);
 476 EXPORT_SYMBOL_GPL(unregister_kprobe);
 477 EXPORT_SYMBOL_GPL(register_jprobe);
 478 EXPORT_SYMBOL_GPL(unregister_jprobe);
 479 EXPORT_SYMBOL_GPL(jprobe_return);
 480 EXPORT_SYMBOL_GPL(register_kretprobe);
 481 EXPORT_SYMBOL_GPL(unregister_kretprobe);
 482