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