arch/ppc64/kernel/kprobes.c

   1 /*
   2  *  Kernel Probes (KProbes)
   3  *  arch/ppc64/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 contributions from
  23  *              Rusty Russell).
  24  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  25  *              interface to access function arguments.
  26  * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
  27  *              for PPC64
  28  */
  29
  30 #include <linux/config.h>
  31 #include <linux/kprobes.h>
  32 #include <linux/ptrace.h>
  33 #include <linux/spinlock.h>
  34 #include <linux/preempt.h>
  35 #include <asm/cacheflush.h>
  36 #include <asm/kdebug.h>
  37 #include <asm/sstep.h>
  38
  39 static DECLARE_MUTEX(kprobe_mutex);
  40
  41 static struct kprobe *current_kprobe;
  42 static unsigned long kprobe_status, kprobe_saved_msr;
  43 static struct kprobe *kprobe_prev;
  44 static unsigned long kprobe_status_prev, kprobe_saved_msr_prev;
  45 static struct pt_regs jprobe_saved_regs;
  46
  47 int arch_prepare_kprobe(struct kprobe *p)
  48 {
  49         int ret = 0;
  50         kprobe_opcode_t insn = *p->addr;
  51
  52         if ((unsigned long)p->addr & 0x03) {
  53                 printk("Attempt to register kprobe at an unaligned address\n");
  54                 ret = -EINVAL;
  55         } else if (IS_MTMSRD(insn) || IS_RFID(insn)) {
  56                 printk("Cannot register a kprobe on rfid or mtmsrd\n");
  57                 ret = -EINVAL;
  58         }
  59
  60         /* insn must be on a special executable page on ppc64 */
  61         if (!ret) {
  62                 up(&kprobe_mutex);
  63                 p->ainsn.insn = get_insn_slot();
  64                 down(&kprobe_mutex);
  65                 if (!p->ainsn.insn)
  66                         ret = -ENOMEM;
  67         }
  68         return ret;
  69 }
  70
  71 void arch_copy_kprobe(struct kprobe *p)
  72 {
  73         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  74         p->opcode = *p->addr;
  75 }
  76
  77 void arch_arm_kprobe(struct kprobe *p)
  78 {
  79         *p->addr = BREAKPOINT_INSTRUCTION;
  80         flush_icache_range((unsigned long) p->addr,
  81                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  82 }
  83
  84 void arch_disarm_kprobe(struct kprobe *p)
  85 {
  86         *p->addr = p->opcode;
  87         flush_icache_range((unsigned long) p->addr,
  88                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  89 }
  90
  91 void arch_remove_kprobe(struct kprobe *p)
  92 {
  93         up(&kprobe_mutex);
  94         free_insn_slot(p->ainsn.insn);
  95         down(&kprobe_mutex);
  96 }
  97
  98 static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
  99 {
 100         kprobe_opcode_t insn = *p->ainsn.insn;
 101
 102         regs->msr |= MSR_SE;
 103
 104         /* single step inline if it is a trap variant */
 105         if (IS_TW(insn) || IS_TD(insn) || IS_TWI(insn) || IS_TDI(insn))
 106                 regs->nip = (unsigned long)p->addr;
 107         else
 108                 regs->nip = (unsigned long)p->ainsn.insn;
 109 }
 110
 111 static inline void save_previous_kprobe(void)
 112 {
 113         kprobe_prev = current_kprobe;
 114         kprobe_status_prev = kprobe_status;
 115         kprobe_saved_msr_prev = kprobe_saved_msr;
 116 }
 117
 118 static inline void restore_previous_kprobe(void)
 119 {
 120         current_kprobe = kprobe_prev;
 121         kprobe_status = kprobe_status_prev;
 122         kprobe_saved_msr = kprobe_saved_msr_prev;
 123 }
 124
 125 void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs)
 126 {
 127         struct kretprobe_instance *ri;
 128
 129         if ((ri = get_free_rp_inst(rp)) != NULL) {
 130                 ri->rp = rp;
 131                 ri->task = current;
 132                 ri->ret_addr = (kprobe_opcode_t *)regs->link;
 133
 134                 /* Replace the return addr with trampoline addr */
 135                 regs->link = (unsigned long)kretprobe_trampoline;
 136                 add_rp_inst(ri);
 137         } else {
 138                 rp->nmissed++;
 139         }
 140 }
 141
 142 static inline int kprobe_handler(struct pt_regs *regs)
 143 {
 144         struct kprobe *p;
 145         int ret = 0;
 146         unsigned int *addr = (unsigned int *)regs->nip;
 147
 148         /* Check we're not actually recursing */
 149         if (kprobe_running()) {
 150                 /* We *are* holding lock here, so this is safe.
 151                    Disarm the probe we just hit, and ignore it. */
 152                 p = get_kprobe(addr);
 153                 if (p) {
 154                         if (kprobe_status == KPROBE_HIT_SS) {
 155                                 regs->msr &= ~MSR_SE;
 156                                 regs->msr |= kprobe_saved_msr;
 157                                 unlock_kprobes();
 158                                 goto no_kprobe;
 159                         }
 160                         /* We have reentered the kprobe_handler(), since
 161                          * another probe was hit while within the handler.
 162                          * We here save the original kprobes variables and
 163                          * just single step on the instruction of the new probe
 164                          * without calling any user handlers.
 165                          */
 166                         save_previous_kprobe();
 167                         current_kprobe = p;
 168                         kprobe_saved_msr = regs->msr;
 169                         p->nmissed++;
 170                         prepare_singlestep(p, regs);
 171                         kprobe_status = KPROBE_REENTER;
 172                         return 1;
 173                 } else {
 174                         p = current_kprobe;
 175                         if (p->break_handler && p->break_handler(p, regs)) {
 176                                 goto ss_probe;
 177                         }
 178                 }
 179                 /* If it's not ours, can't be delete race, (we hold lock). */
 180                 goto no_kprobe;
 181         }
 182
 183         lock_kprobes();
 184         p = get_kprobe(addr);
 185         if (!p) {
 186                 unlock_kprobes();
 187                 if (*addr != BREAKPOINT_INSTRUCTION) {
 188                         /*
 189                          * PowerPC has multiple variants of the "trap"
 190                          * instruction. If the current instruction is a
 191                          * trap variant, it could belong to someone else
 192                          */
 193                         kprobe_opcode_t cur_insn = *addr;
 194                         if (IS_TW(cur_insn) || IS_TD(cur_insn) ||
 195                                         IS_TWI(cur_insn) || IS_TDI(cur_insn))
 196                                 goto no_kprobe;
 197                         /*
 198                          * The breakpoint instruction was removed right
 199                          * after we hit it.  Another cpu has removed
 200                          * either a probepoint or a debugger breakpoint
 201                          * at this address.  In either case, no further
 202                          * handling of this interrupt is appropriate.
 203                          */
 204                         ret = 1;
 205                 }
 206                 /* Not one of ours: let kernel handle it */
 207                 goto no_kprobe;
 208         }
 209
 210         kprobe_status = KPROBE_HIT_ACTIVE;
 211         current_kprobe = p;
 212         kprobe_saved_msr = regs->msr;
 213         if (p->pre_handler && p->pre_handler(p, regs))
 214                 /* handler has already set things up, so skip ss setup */
 215                 return 1;
 216
 217 ss_probe:
 218         prepare_singlestep(p, regs);
 219         kprobe_status = KPROBE_HIT_SS;
 220         /*
 221          * This preempt_disable() matches the preempt_enable_no_resched()
 222          * in post_kprobe_handler().
 223          */
 224         preempt_disable();
 225         return 1;
 226
 227 no_kprobe:
 228         return ret;
 229 }
 230
 231 /*
 232  * Function return probe trampoline:
 233  *      - init_kprobes() establishes a probepoint here
 234  *      - When the probed function returns, this probe
 235  *              causes the handlers to fire
 236  */
 237 void kretprobe_trampoline_holder(void)
 238 {
 239         asm volatile(".global kretprobe_trampoline\n"
 240                         "kretprobe_trampoline:\n"
 241                         "nop\n");
 242 }
 243
 244 /*
 245  * Called when the probe at kretprobe trampoline is hit
 246  */
 247 int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 248 {
 249         struct kretprobe_instance *ri = NULL;
 250         struct hlist_head *head;
 251         struct hlist_node *node, *tmp;
 252         unsigned long orig_ret_address = 0;
 253         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 254
 255         head = kretprobe_inst_table_head(current);
 256
 257         /*
 258          * It is possible to have multiple instances associated with a given
 259          * task either because an multiple functions in the call path
 260          * have a return probe installed on them, and/or more then one return
 261          * return probe was registered for a target function.
 262          *
 263          * We can handle this because:
 264          *     - instances are always inserted at the head of the list
 265          *     - when multiple return probes are registered for the same
 266          *       function, the first instance's ret_addr will point to the
 267          *       real return address, and all the rest will point to
 268          *       kretprobe_trampoline
 269          */
 270         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 271                 if (ri->task != current)
 272                         /* another task is sharing our hash bucket */
 273                         continue;
 274
 275                 if (ri->rp && ri->rp->handler)
 276                         ri->rp->handler(ri, regs);
 277
 278                 orig_ret_address = (unsigned long)ri->ret_addr;
 279                 recycle_rp_inst(ri);
 280
 281                 if (orig_ret_address != trampoline_address)
 282                         /*
 283                          * This is the real return address. Any other
 284                          * instances associated with this task are for
 285                          * other calls deeper on the call stack
 286                          */
 287                         break;
 288         }
 289
 290         BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
 291         regs->nip = orig_ret_address;
 292
 293         unlock_kprobes();
 294
 295         /*
 296          * By returning a non-zero value, we are telling
 297          * kprobe_handler() that we have handled unlocking
 298          * and re-enabling preemption.
 299          */
 300         return 1;
 301 }
 302
 303 /*
 304  * Called after single-stepping.  p->addr is the address of the
 305  * instruction whose first byte has been replaced by the "breakpoint"
 306  * instruction.  To avoid the SMP problems that can occur when we
 307  * temporarily put back the original opcode to single-step, we
 308  * single-stepped a copy of the instruction.  The address of this
 309  * copy is p->ainsn.insn.
 310  */
 311 static void resume_execution(struct kprobe *p, struct pt_regs *regs)
 312 {
 313         int ret;
 314         unsigned int insn = *p->ainsn.insn;
 315
 316         regs->nip = (unsigned long)p->addr;
 317         ret = emulate_step(regs, insn);
 318         if (ret == 0)
 319                 regs->nip = (unsigned long)p->addr + 4;
 320 }
 321
 322 static inline int post_kprobe_handler(struct pt_regs *regs)
 323 {
 324         if (!kprobe_running())
 325                 return 0;
 326
 327         if ((kprobe_status != KPROBE_REENTER) && current_kprobe->post_handler) {
 328                 kprobe_status = KPROBE_HIT_SSDONE;
 329                 current_kprobe->post_handler(current_kprobe, regs, 0);
 330         }
 331
 332         resume_execution(current_kprobe, regs);
 333         regs->msr |= kprobe_saved_msr;
 334
 335         /*Restore back the original saved kprobes variables and continue. */
 336         if (kprobe_status == KPROBE_REENTER) {
 337                 restore_previous_kprobe();
 338                 goto out;
 339         }
 340         unlock_kprobes();
 341 out:
 342         preempt_enable_no_resched();
 343
 344         /*
 345          * if somebody else is singlestepping across a probe point, msr
 346          * will have SE set, in which case, continue the remaining processing
 347          * of do_debug, as if this is not a probe hit.
 348          */
 349         if (regs->msr & MSR_SE)
 350                 return 0;
 351
 352         return 1;
 353 }
 354
 355 /* Interrupts disabled, kprobe_lock held. */
 356 static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 357 {
 358         if (current_kprobe->fault_handler
 359             && current_kprobe->fault_handler(current_kprobe, regs, trapnr))
 360                 return 1;
 361
 362         if (kprobe_status & KPROBE_HIT_SS) {
 363                 resume_execution(current_kprobe, regs);
 364                 regs->msr &= ~MSR_SE;
 365                 regs->msr |= kprobe_saved_msr;
 366
 367                 unlock_kprobes();
 368                 preempt_enable_no_resched();
 369         }
 370         return 0;
 371 }
 372
 373 /*
 374  * Wrapper routine to for handling exceptions.
 375  */
 376 int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
 377                              void *data)
 378 {
 379         struct die_args *args = (struct die_args *)data;
 380         int ret = NOTIFY_DONE;
 381
 382         /*
 383          * Interrupts are not disabled here.  We need to disable
 384          * preemption, because kprobe_running() uses smp_processor_id().
 385          */
 386         preempt_disable();
 387         switch (val) {
 388         case DIE_BPT:
 389                 if (kprobe_handler(args->regs))
 390                         ret = NOTIFY_STOP;
 391                 break;
 392         case DIE_SSTEP:
 393                 if (post_kprobe_handler(args->regs))
 394                         ret = NOTIFY_STOP;
 395                 break;
 396         case DIE_GPF:
 397         case DIE_PAGE_FAULT:
 398                 if (kprobe_running() &&
 399                     kprobe_fault_handler(args->regs, args->trapnr))
 400                         ret = NOTIFY_STOP;
 401                 break;
 402         default:
 403                 break;
 404         }
 405         preempt_enable();
 406         return ret;
 407 }
 408
 409 int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 410 {
 411         struct jprobe *jp = container_of(p, struct jprobe, kp);
 412
 413         memcpy(&jprobe_saved_regs, regs, sizeof(struct pt_regs));
 414
 415         /* setup return addr to the jprobe handler routine */
 416         regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
 417         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 418
 419         return 1;
 420 }
 421
 422 void jprobe_return(void)
 423 {
 424         asm volatile("trap" ::: "memory");
 425 }
 426
 427 void jprobe_return_end(void)
 428 {
 429 };
 430
 431 int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 432 {
 433         /*
 434          * FIXME - we should ideally be validating that we got here 'cos
 435          * of the "trap" in jprobe_return() above, before restoring the
 436          * saved regs...
 437          */
 438         memcpy(regs, &jprobe_saved_regs, sizeof(struct pt_regs));
 439         return 1;
 440 }
 441
 442 static struct kprobe trampoline_p = {
 443         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 444         .pre_handler = trampoline_probe_handler
 445 };
 446
 447 int __init arch_init_kprobes(void)
 448 {
 449         return register_kprobe(&trampoline_p);
 450 }