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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 <asm/cacheflush.h>
34 #include <asm/kdebug.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, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
63                 p->opcode = *p->addr;
64                 flush_icache_range((unsigned long)p->ainsn.insn,
65                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
66         }
67
68         return ret;
69 }
70
71 void __kprobes arch_arm_kprobe(struct kprobe *p)
72 {
73         *p->addr = BREAKPOINT_INSTRUCTION;
74         flush_icache_range((unsigned long) p->addr,
75                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
76 }
77
78 void __kprobes arch_disarm_kprobe(struct kprobe *p)
79 {
80         *p->addr = p->opcode;
81         flush_icache_range((unsigned long) p->addr,
82                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
83 }
84
85 void __kprobes arch_remove_kprobe(struct kprobe *p)
86 {
87         mutex_lock(&kprobe_mutex);
88         free_insn_slot(p->ainsn.insn, 0);
89         mutex_unlock(&kprobe_mutex);
90 }
91
92 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
93 {
94         regs->msr |= MSR_SE;
95
96         /*
97          * On powerpc we should single step on the original
98          * instruction even if the probed insn is a trap
99          * variant as values in regs could play a part in
100          * if the trap is taken or not
101          */
102         regs->nip = (unsigned long)p->ainsn.insn;
103 }
104
105 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
106 {
107         kcb->prev_kprobe.kp = kprobe_running();
108         kcb->prev_kprobe.status = kcb->kprobe_status;
109         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
110 }
111
112 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
113 {
114         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
115         kcb->kprobe_status = kcb->prev_kprobe.status;
116         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
117 }
118
119 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
120                                 struct kprobe_ctlblk *kcb)
121 {
122         __get_cpu_var(current_kprobe) = p;
123         kcb->kprobe_saved_msr = regs->msr;
124 }
125
126 /* Called with kretprobe_lock held */
127 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
128                                       struct pt_regs *regs)
129 {
130         struct kretprobe_instance *ri;
131
132         if ((ri = get_free_rp_inst(rp)) != NULL) {
133                 ri->rp = rp;
134                 ri->task = current;
135                 ri->ret_addr = (kprobe_opcode_t *)regs->link;
136
137                 /* Replace the return addr with trampoline addr */
138                 regs->link = (unsigned long)kretprobe_trampoline;
139                 add_rp_inst(ri);
140         } else {
141                 rp->nmissed++;
142         }
143 }
144
145 static int __kprobes kprobe_handler(struct pt_regs *regs)
146 {
147         struct kprobe *p;
148         int ret = 0;
149         unsigned int *addr = (unsigned int *)regs->nip;
150         struct kprobe_ctlblk *kcb;
151
152         /*
153          * We don't want to be preempted for the entire
154          * duration of kprobe processing
155          */
156         preempt_disable();
157         kcb = get_kprobe_ctlblk();
158
159         /* Check we're not actually recursing */
160         if (kprobe_running()) {
161                 p = get_kprobe(addr);
162                 if (p) {
163                         kprobe_opcode_t insn = *p->ainsn.insn;
164                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
165                                         is_trap(insn)) {
166                                 regs->msr &= ~MSR_SE;
167                                 regs->msr |= kcb->kprobe_saved_msr;
168                                 goto no_kprobe;
169                         }
170                         /* We have reentered the kprobe_handler(), since
171                          * another probe was hit while within the handler.
172                          * We here save the original kprobes variables and
173                          * just single step on the instruction of the new probe
174                          * without calling any user handlers.
175                          */
176                         save_previous_kprobe(kcb);
177                         set_current_kprobe(p, regs, kcb);
178                         kcb->kprobe_saved_msr = regs->msr;
179                         kprobes_inc_nmissed_count(p);
180                         prepare_singlestep(p, regs);
181                         kcb->kprobe_status = KPROBE_REENTER;
182                         return 1;
183                 } else {
184                         if (*addr != BREAKPOINT_INSTRUCTION) {
185                                 /* If trap variant, then it belongs not to us */
186                                 kprobe_opcode_t cur_insn = *addr;
187                                 if (is_trap(cur_insn))
188                                         goto no_kprobe;
189                                 /* The breakpoint instruction was removed by
190                                  * another cpu right after we hit, no further
191                                  * handling of this interrupt is appropriate
192                                  */
193                                 ret = 1;
194                                 goto no_kprobe;
195                         }
196                         p = __get_cpu_var(current_kprobe);
197                         if (p->break_handler && p->break_handler(p, regs)) {
198                                 goto ss_probe;
199                         }
200                 }
201                 goto no_kprobe;
202         }
203
204         p = get_kprobe(addr);
205         if (!p) {
206                 if (*addr != BREAKPOINT_INSTRUCTION) {
207                         /*
208                          * PowerPC has multiple variants of the "trap"
209                          * instruction. If the current instruction is a
210                          * trap variant, it could belong to someone else
211                          */
212                         kprobe_opcode_t cur_insn = *addr;
213                         if (is_trap(cur_insn))
214                                 goto no_kprobe;
215                         /*
216                          * The breakpoint instruction was removed right
217                          * after we hit it.  Another cpu has removed
218                          * either a probepoint or a debugger breakpoint
219                          * at this address.  In either case, no further
220                          * handling of this interrupt is appropriate.
221                          */
222                         ret = 1;
223                 }
224                 /* Not one of ours: let kernel handle it */
225                 goto no_kprobe;
226         }
227
228         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
229         set_current_kprobe(p, regs, kcb);
230         if (p->pre_handler && p->pre_handler(p, regs))
231                 /* handler has already set things up, so skip ss setup */
232                 return 1;
233
234 ss_probe:
235         prepare_singlestep(p, regs);
236         kcb->kprobe_status = KPROBE_HIT_SS;
237         return 1;
238
239 no_kprobe:
240         preempt_enable_no_resched();
241         return ret;
242 }
243
244 /*
245  * Function return probe trampoline:
246  *      - init_kprobes() establishes a probepoint here
247  *      - When the probed function returns, this probe
248  *              causes the handlers to fire
249  */
250 void kretprobe_trampoline_holder(void)
251 {
252         asm volatile(".global kretprobe_trampoline\n"
253                         "kretprobe_trampoline:\n"
254                         "nop\n");
255 }
256
257 /*
258  * Called when the probe at kretprobe trampoline is hit
259  */
260 int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
261 {
262         struct kretprobe_instance *ri = NULL;
263         struct hlist_head *head, empty_rp;
264         struct hlist_node *node, *tmp;
265         unsigned long flags, orig_ret_address = 0;
266         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
267
268         INIT_HLIST_HEAD(&empty_rp);
269         spin_lock_irqsave(&kretprobe_lock, flags);
270         head = kretprobe_inst_table_head(current);
271
272         /*
273          * It is possible to have multiple instances associated with a given
274          * task either because an multiple functions in the call path
275          * have a return probe installed on them, and/or more then one return
276          * return probe was registered for a target function.
277          *
278          * We can handle this because:
279          *     - instances are always inserted at the head of the list
280          *     - when multiple return probes are registered for the same
281          *       function, the first instance's ret_addr will point to the
282          *       real return address, and all the rest will point to
283          *       kretprobe_trampoline
284          */
285         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
286                 if (ri->task != current)
287                         /* another task is sharing our hash bucket */
288                         continue;
289
290                 if (ri->rp && ri->rp->handler)
291                         ri->rp->handler(ri, regs);
292
293                 orig_ret_address = (unsigned long)ri->ret_addr;
294                 recycle_rp_inst(ri, &empty_rp);
295
296                 if (orig_ret_address != trampoline_address)
297                         /*
298                          * This is the real return address. Any other
299                          * instances associated with this task are for
300                          * other calls deeper on the call stack
301                          */
302                         break;
303         }
304
305         BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
306         regs->nip = orig_ret_address;
307
308         reset_current_kprobe();
309         spin_unlock_irqrestore(&kretprobe_lock, flags);
310         preempt_enable_no_resched();
311
312         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
313                 hlist_del(&ri->hlist);
314                 kfree(ri);
315         }
316         /*
317          * By returning a non-zero value, we are telling
318          * kprobe_handler() that we don't want the post_handler
319          * to run (and have re-enabled preemption)
320          */
321         return 1;
322 }
323
324 /*
325  * Called after single-stepping.  p->addr is the address of the
326  * instruction whose first byte has been replaced by the "breakpoint"
327  * instruction.  To avoid the SMP problems that can occur when we
328  * temporarily put back the original opcode to single-step, we
329  * single-stepped a copy of the instruction.  The address of this
330  * copy is p->ainsn.insn.
331  */
332 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
333 {
334         int ret;
335         unsigned int insn = *p->ainsn.insn;
336
337         regs->nip = (unsigned long)p->addr;
338         ret = emulate_step(regs, insn);
339         if (ret == 0)
340                 regs->nip = (unsigned long)p->addr + 4;
341 }
342
343 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
344 {
345         struct kprobe *cur = kprobe_running();
346         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
347
348         if (!cur)
349                 return 0;
350
351         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
352                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
353                 cur->post_handler(cur, regs, 0);
354         }
355
356         resume_execution(cur, regs);
357         regs->msr |= kcb->kprobe_saved_msr;
358
359         /*Restore back the original saved kprobes variables and continue. */
360         if (kcb->kprobe_status == KPROBE_REENTER) {
361                 restore_previous_kprobe(kcb);
362                 goto out;
363         }
364         reset_current_kprobe();
365 out:
366         preempt_enable_no_resched();
367
368         /*
369          * if somebody else is singlestepping across a probe point, msr
370          * will have SE set, in which case, continue the remaining processing
371          * of do_debug, as if this is not a probe hit.
372          */
373         if (regs->msr & MSR_SE)
374                 return 0;
375
376         return 1;
377 }
378
379 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
380 {
381         struct kprobe *cur = kprobe_running();
382         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
383         const struct exception_table_entry *entry;
384
385         switch(kcb->kprobe_status) {
386         case KPROBE_HIT_SS:
387         case KPROBE_REENTER:
388                 /*
389                  * We are here because the instruction being single
390                  * stepped caused a page fault. We reset the current
391                  * kprobe and the nip points back to the probe address
392                  * and allow the page fault handler to continue as a
393                  * normal page fault.
394                  */
395                 regs->nip = (unsigned long)cur->addr;
396                 regs->msr &= ~MSR_SE;
397                 regs->msr |= kcb->kprobe_saved_msr;
398                 if (kcb->kprobe_status == KPROBE_REENTER)
399                         restore_previous_kprobe(kcb);
400                 else
401                         reset_current_kprobe();
402                 preempt_enable_no_resched();
403                 break;
404         case KPROBE_HIT_ACTIVE:
405         case KPROBE_HIT_SSDONE:
406                 /*
407                  * We increment the nmissed count for accounting,
408                  * we can also use npre/npostfault count for accouting
409                  * these specific fault cases.
410                  */
411                 kprobes_inc_nmissed_count(cur);
412
413                 /*
414                  * We come here because instructions in the pre/post
415                  * handler caused the page_fault, this could happen
416                  * if handler tries to access user space by
417                  * copy_from_user(), get_user() etc. Let the
418                  * user-specified handler try to fix it first.
419                  */
420                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
421                         return 1;
422
423                 /*
424                  * In case the user-specified fault handler returned
425                  * zero, try to fix up.
426                  */
427                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
428                         regs->nip = entry->fixup;
429                         return 1;
430                 }
431
432                 /*
433                  * fixup_exception() could not handle it,
434                  * Let do_page_fault() fix it.
435                  */
436                 break;
437         default:
438                 break;
439         }
440         return 0;
441 }
442
443 /*
444  * Wrapper routine to for handling exceptions.
445  */
446 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
447                                        unsigned long val, void *data)
448 {
449         struct die_args *args = (struct die_args *)data;
450         int ret = NOTIFY_DONE;
451
452         if (args->regs && user_mode(args->regs))
453                 return ret;
454
455         switch (val) {
456         case DIE_BPT:
457                 if (kprobe_handler(args->regs))
458                         ret = NOTIFY_STOP;
459                 break;
460         case DIE_SSTEP:
461                 if (post_kprobe_handler(args->regs))
462                         ret = NOTIFY_STOP;
463                 break;
464         case DIE_PAGE_FAULT:
465                 /* kprobe_running() needs smp_processor_id() */
466                 preempt_disable();
467                 if (kprobe_running() &&
468                     kprobe_fault_handler(args->regs, args->trapnr))
469                         ret = NOTIFY_STOP;
470                 preempt_enable();
471                 break;
472         default:
473                 break;
474         }
475         return ret;
476 }
477
478 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
479 {
480         struct jprobe *jp = container_of(p, struct jprobe, kp);
481         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
482
483         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
484
485         /* setup return addr to the jprobe handler routine */
486 #ifdef CONFIG_PPC64
487         regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
488         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
489 #else
490         regs->nip = (unsigned long)jp->entry;
491 #endif
492
493         return 1;
494 }
495
496 void __kprobes jprobe_return(void)
497 {
498         asm volatile("trap" ::: "memory");
499 }
500
501 void __kprobes jprobe_return_end(void)
502 {
503 };
504
505 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
506 {
507         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
508
509         /*
510          * FIXME - we should ideally be validating that we got here 'cos
511          * of the "trap" in jprobe_return() above, before restoring the
512          * saved regs...
513          */
514         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
515         preempt_enable_no_resched();
516         return 1;
517 }
518
519 static struct kprobe trampoline_p = {
520         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
521         .pre_handler = trampoline_probe_handler
522 };
523
524 int __init arch_init_kprobes(void)
525 {
526         return register_kprobe(&trampoline_p);
527 }