3d54ad7dd1f9150afc9c12e118686cf523da7254
[linux-2.6.git] / arch / powerpc / kernel / kprobes.c
1 /*
2  *  Kernel Probes (KProbes)
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17  *
18  * Copyright (C) IBM Corporation, 2002, 2004
19  *
20  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
21  *              Probes initial implementation ( includes contributions from
22  *              Rusty Russell).
23  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
24  *              interface to access function arguments.
25  * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
26  *              for PPC64
27  */
28
29 #include <linux/kprobes.h>
30 #include <linux/ptrace.h>
31 #include <linux/preempt.h>
32 #include <linux/module.h>
33 #include <linux/kdebug.h>
34 #include <asm/cacheflush.h>
35 #include <asm/sstep.h>
36 #include <asm/uaccess.h>
37
38 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
39 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
40
41 int __kprobes arch_prepare_kprobe(struct kprobe *p)
42 {
43         int ret = 0;
44         kprobe_opcode_t insn = *p->addr;
45
46         if ((unsigned long)p->addr & 0x03) {
47                 printk("Attempt to register kprobe at an unaligned address\n");
48                 ret = -EINVAL;
49         } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
50                 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
51                 ret = -EINVAL;
52         }
53
54         /* insn must be on a special executable page on ppc64 */
55         if (!ret) {
56                 p->ainsn.insn = get_insn_slot();
57                 if (!p->ainsn.insn)
58                         ret = -ENOMEM;
59         }
60
61         if (!ret) {
62                 memcpy(p->ainsn.insn, p->addr,
63                                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
64                 p->opcode = *p->addr;
65                 flush_icache_range((unsigned long)p->ainsn.insn,
66                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
67         }
68
69         p->ainsn.boostable = 0;
70         return ret;
71 }
72
73 void __kprobes arch_arm_kprobe(struct kprobe *p)
74 {
75         *p->addr = BREAKPOINT_INSTRUCTION;
76         flush_icache_range((unsigned long) p->addr,
77                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
78 }
79
80 void __kprobes arch_disarm_kprobe(struct kprobe *p)
81 {
82         *p->addr = p->opcode;
83         flush_icache_range((unsigned long) p->addr,
84                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
85 }
86
87 void __kprobes arch_remove_kprobe(struct kprobe *p)
88 {
89         mutex_lock(&kprobe_mutex);
90         free_insn_slot(p->ainsn.insn, 0);
91         mutex_unlock(&kprobe_mutex);
92 }
93
94 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
95 {
96         regs->msr |= MSR_SE;
97
98         /*
99          * On powerpc we should single step on the original
100          * instruction even if the probed insn is a trap
101          * variant as values in regs could play a part in
102          * if the trap is taken or not
103          */
104         regs->nip = (unsigned long)p->ainsn.insn;
105 }
106
107 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
108 {
109         kcb->prev_kprobe.kp = kprobe_running();
110         kcb->prev_kprobe.status = kcb->kprobe_status;
111         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
112 }
113
114 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
115 {
116         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
117         kcb->kprobe_status = kcb->prev_kprobe.status;
118         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
119 }
120
121 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
122                                 struct kprobe_ctlblk *kcb)
123 {
124         __get_cpu_var(current_kprobe) = p;
125         kcb->kprobe_saved_msr = regs->msr;
126 }
127
128 /* Called with kretprobe_lock held */
129 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
130                                       struct pt_regs *regs)
131 {
132         struct kretprobe_instance *ri;
133
134         if ((ri = get_free_rp_inst(rp)) != NULL) {
135                 ri->rp = rp;
136                 ri->task = current;
137                 ri->ret_addr = (kprobe_opcode_t *)regs->link;
138
139                 /* Replace the return addr with trampoline addr */
140                 regs->link = (unsigned long)kretprobe_trampoline;
141                 add_rp_inst(ri);
142         } else {
143                 rp->nmissed++;
144         }
145 }
146
147 static int __kprobes kprobe_handler(struct pt_regs *regs)
148 {
149         struct kprobe *p;
150         int ret = 0;
151         unsigned int *addr = (unsigned int *)regs->nip;
152         struct kprobe_ctlblk *kcb;
153
154         /*
155          * We don't want to be preempted for the entire
156          * duration of kprobe processing
157          */
158         preempt_disable();
159         kcb = get_kprobe_ctlblk();
160
161         /* Check we're not actually recursing */
162         if (kprobe_running()) {
163                 p = get_kprobe(addr);
164                 if (p) {
165                         kprobe_opcode_t insn = *p->ainsn.insn;
166                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
167                                         is_trap(insn)) {
168                                 regs->msr &= ~MSR_SE;
169                                 regs->msr |= kcb->kprobe_saved_msr;
170                                 goto no_kprobe;
171                         }
172                         /* We have reentered the kprobe_handler(), since
173                          * another probe was hit while within the handler.
174                          * We here save the original kprobes variables and
175                          * just single step on the instruction of the new probe
176                          * without calling any user handlers.
177                          */
178                         save_previous_kprobe(kcb);
179                         set_current_kprobe(p, regs, kcb);
180                         kcb->kprobe_saved_msr = regs->msr;
181                         kprobes_inc_nmissed_count(p);
182                         prepare_singlestep(p, regs);
183                         kcb->kprobe_status = KPROBE_REENTER;
184                         return 1;
185                 } else {
186                         if (*addr != BREAKPOINT_INSTRUCTION) {
187                                 /* If trap variant, then it belongs not to us */
188                                 kprobe_opcode_t cur_insn = *addr;
189                                 if (is_trap(cur_insn))
190                                         goto no_kprobe;
191                                 /* The breakpoint instruction was removed by
192                                  * another cpu right after we hit, no further
193                                  * handling of this interrupt is appropriate
194                                  */
195                                 ret = 1;
196                                 goto no_kprobe;
197                         }
198                         p = __get_cpu_var(current_kprobe);
199                         if (p->break_handler && p->break_handler(p, regs)) {
200                                 goto ss_probe;
201                         }
202                 }
203                 goto no_kprobe;
204         }
205
206         p = get_kprobe(addr);
207         if (!p) {
208                 if (*addr != BREAKPOINT_INSTRUCTION) {
209                         /*
210                          * PowerPC has multiple variants of the "trap"
211                          * instruction. If the current instruction is a
212                          * trap variant, it could belong to someone else
213                          */
214                         kprobe_opcode_t cur_insn = *addr;
215                         if (is_trap(cur_insn))
216                                 goto no_kprobe;
217                         /*
218                          * The breakpoint instruction was removed right
219                          * after we hit it.  Another cpu has removed
220                          * either a probepoint or a debugger breakpoint
221                          * at this address.  In either case, no further
222                          * handling of this interrupt is appropriate.
223                          */
224                         ret = 1;
225                 }
226                 /* Not one of ours: let kernel handle it */
227                 goto no_kprobe;
228         }
229
230         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
231         set_current_kprobe(p, regs, kcb);
232         if (p->pre_handler && p->pre_handler(p, regs))
233                 /* handler has already set things up, so skip ss setup */
234                 return 1;
235
236 ss_probe:
237         if (p->ainsn.boostable >= 0) {
238                 unsigned int insn = *p->ainsn.insn;
239
240                 /* regs->nip is also adjusted if emulate_step returns 1 */
241                 ret = emulate_step(regs, insn);
242                 if (ret > 0) {
243                         /*
244                          * Once this instruction has been boosted
245                          * successfully, set the boostable flag
246                          */
247                         if (unlikely(p->ainsn.boostable == 0))
248                                 p->ainsn.boostable = 1;
249
250                         if (p->post_handler)
251                                 p->post_handler(p, regs, 0);
252
253                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
254                         reset_current_kprobe();
255                         preempt_enable_no_resched();
256                         return 1;
257                 } else if (ret < 0) {
258                         /*
259                          * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
260                          * So, we should never get here... but, its still
261                          * good to catch them, just in case...
262                          */
263                         printk("Can't step on instruction %x\n", insn);
264                         BUG();
265                 } else if (ret == 0)
266                         /* This instruction can't be boosted */
267                         p->ainsn.boostable = -1;
268         }
269         prepare_singlestep(p, regs);
270         kcb->kprobe_status = KPROBE_HIT_SS;
271         return 1;
272
273 no_kprobe:
274         preempt_enable_no_resched();
275         return ret;
276 }
277
278 /*
279  * Function return probe trampoline:
280  *      - init_kprobes() establishes a probepoint here
281  *      - When the probed function returns, this probe
282  *              causes the handlers to fire
283  */
284 void kretprobe_trampoline_holder(void)
285 {
286         asm volatile(".global kretprobe_trampoline\n"
287                         "kretprobe_trampoline:\n"
288                         "nop\n");
289 }
290
291 /*
292  * Called when the probe at kretprobe trampoline is hit
293  */
294 int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
295 {
296         struct kretprobe_instance *ri = NULL;
297         struct hlist_head *head, empty_rp;
298         struct hlist_node *node, *tmp;
299         unsigned long flags, orig_ret_address = 0;
300         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
301
302         INIT_HLIST_HEAD(&empty_rp);
303         spin_lock_irqsave(&kretprobe_lock, flags);
304         head = kretprobe_inst_table_head(current);
305
306         /*
307          * It is possible to have multiple instances associated with a given
308          * task either because an multiple functions in the call path
309          * have a return probe installed on them, and/or more then one return
310          * return probe was registered for a target function.
311          *
312          * We can handle this because:
313          *     - instances are always inserted at the head of the list
314          *     - when multiple return probes are registered for the same
315          *       function, the first instance's ret_addr will point to the
316          *       real return address, and all the rest will point to
317          *       kretprobe_trampoline
318          */
319         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
320                 if (ri->task != current)
321                         /* another task is sharing our hash bucket */
322                         continue;
323
324                 if (ri->rp && ri->rp->handler)
325                         ri->rp->handler(ri, regs);
326
327                 orig_ret_address = (unsigned long)ri->ret_addr;
328                 recycle_rp_inst(ri, &empty_rp);
329
330                 if (orig_ret_address != trampoline_address)
331                         /*
332                          * This is the real return address. Any other
333                          * instances associated with this task are for
334                          * other calls deeper on the call stack
335                          */
336                         break;
337         }
338
339         kretprobe_assert(ri, orig_ret_address, trampoline_address);
340         regs->nip = orig_ret_address;
341
342         reset_current_kprobe();
343         spin_unlock_irqrestore(&kretprobe_lock, flags);
344         preempt_enable_no_resched();
345
346         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
347                 hlist_del(&ri->hlist);
348                 kfree(ri);
349         }
350         /*
351          * By returning a non-zero value, we are telling
352          * kprobe_handler() that we don't want the post_handler
353          * to run (and have re-enabled preemption)
354          */
355         return 1;
356 }
357
358 /*
359  * Called after single-stepping.  p->addr is the address of the
360  * instruction whose first byte has been replaced by the "breakpoint"
361  * instruction.  To avoid the SMP problems that can occur when we
362  * temporarily put back the original opcode to single-step, we
363  * single-stepped a copy of the instruction.  The address of this
364  * copy is p->ainsn.insn.
365  */
366 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
367 {
368         int ret;
369         unsigned int insn = *p->ainsn.insn;
370
371         regs->nip = (unsigned long)p->addr;
372         ret = emulate_step(regs, insn);
373         if (ret == 0)
374                 regs->nip = (unsigned long)p->addr + 4;
375 }
376
377 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
378 {
379         struct kprobe *cur = kprobe_running();
380         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
381
382         if (!cur)
383                 return 0;
384
385         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
386                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
387                 cur->post_handler(cur, regs, 0);
388         }
389
390         resume_execution(cur, regs);
391         regs->msr |= kcb->kprobe_saved_msr;
392
393         /*Restore back the original saved kprobes variables and continue. */
394         if (kcb->kprobe_status == KPROBE_REENTER) {
395                 restore_previous_kprobe(kcb);
396                 goto out;
397         }
398         reset_current_kprobe();
399 out:
400         preempt_enable_no_resched();
401
402         /*
403          * if somebody else is singlestepping across a probe point, msr
404          * will have SE set, in which case, continue the remaining processing
405          * of do_debug, as if this is not a probe hit.
406          */
407         if (regs->msr & MSR_SE)
408                 return 0;
409
410         return 1;
411 }
412
413 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
414 {
415         struct kprobe *cur = kprobe_running();
416         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
417         const struct exception_table_entry *entry;
418
419         switch(kcb->kprobe_status) {
420         case KPROBE_HIT_SS:
421         case KPROBE_REENTER:
422                 /*
423                  * We are here because the instruction being single
424                  * stepped caused a page fault. We reset the current
425                  * kprobe and the nip points back to the probe address
426                  * and allow the page fault handler to continue as a
427                  * normal page fault.
428                  */
429                 regs->nip = (unsigned long)cur->addr;
430                 regs->msr &= ~MSR_SE;
431                 regs->msr |= kcb->kprobe_saved_msr;
432                 if (kcb->kprobe_status == KPROBE_REENTER)
433                         restore_previous_kprobe(kcb);
434                 else
435                         reset_current_kprobe();
436                 preempt_enable_no_resched();
437                 break;
438         case KPROBE_HIT_ACTIVE:
439         case KPROBE_HIT_SSDONE:
440                 /*
441                  * We increment the nmissed count for accounting,
442                  * we can also use npre/npostfault count for accouting
443                  * these specific fault cases.
444                  */
445                 kprobes_inc_nmissed_count(cur);
446
447                 /*
448                  * We come here because instructions in the pre/post
449                  * handler caused the page_fault, this could happen
450                  * if handler tries to access user space by
451                  * copy_from_user(), get_user() etc. Let the
452                  * user-specified handler try to fix it first.
453                  */
454                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
455                         return 1;
456
457                 /*
458                  * In case the user-specified fault handler returned
459                  * zero, try to fix up.
460                  */
461                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
462                         regs->nip = entry->fixup;
463                         return 1;
464                 }
465
466                 /*
467                  * fixup_exception() could not handle it,
468                  * Let do_page_fault() fix it.
469                  */
470                 break;
471         default:
472                 break;
473         }
474         return 0;
475 }
476
477 /*
478  * Wrapper routine to for handling exceptions.
479  */
480 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
481                                        unsigned long val, void *data)
482 {
483         struct die_args *args = (struct die_args *)data;
484         int ret = NOTIFY_DONE;
485
486         if (args->regs && user_mode(args->regs))
487                 return ret;
488
489         switch (val) {
490         case DIE_BPT:
491                 if (kprobe_handler(args->regs))
492                         ret = NOTIFY_STOP;
493                 break;
494         case DIE_SSTEP:
495                 if (post_kprobe_handler(args->regs))
496                         ret = NOTIFY_STOP;
497                 break;
498         case DIE_PAGE_FAULT:
499                 /* kprobe_running() needs smp_processor_id() */
500                 preempt_disable();
501                 if (kprobe_running() &&
502                     kprobe_fault_handler(args->regs, args->trapnr))
503                         ret = NOTIFY_STOP;
504                 preempt_enable();
505                 break;
506         default:
507                 break;
508         }
509         return ret;
510 }
511
512 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
513 {
514         struct jprobe *jp = container_of(p, struct jprobe, kp);
515         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
516
517         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
518
519         /* setup return addr to the jprobe handler routine */
520 #ifdef CONFIG_PPC64
521         regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
522         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
523 #else
524         regs->nip = (unsigned long)jp->entry;
525 #endif
526
527         return 1;
528 }
529
530 void __kprobes jprobe_return(void)
531 {
532         asm volatile("trap" ::: "memory");
533 }
534
535 void __kprobes jprobe_return_end(void)
536 {
537 };
538
539 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
540 {
541         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
542
543         /*
544          * FIXME - we should ideally be validating that we got here 'cos
545          * of the "trap" in jprobe_return() above, before restoring the
546          * saved regs...
547          */
548         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
549         preempt_enable_no_resched();
550         return 1;
551 }
552
553 static struct kprobe trampoline_p = {
554         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
555         .pre_handler = trampoline_probe_handler
556 };
557
558 int __init arch_init_kprobes(void)
559 {
560         return register_kprobe(&trampoline_p);
561 }