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Linux/arch/powerpc/kernel/kprobes.c

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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 <linux/kdebug.h>
 34 #include <linux/slab.h>
 35 #include <asm/code-patching.h>
 36 #include <asm/cacheflush.h>
 37 #include <asm/sstep.h>
 38 #include <asm/uaccess.h>
 39 
 40 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 41 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 42 
 43 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
 44 
 45 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 46 {
 47         int ret = 0;
 48         kprobe_opcode_t insn = *p->addr;
 49 
 50         if ((unsigned long)p->addr & 0x03) {
 51                 printk("Attempt to register kprobe at an unaligned address\n");
 52                 ret = -EINVAL;
 53         } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
 54                 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
 55                 ret = -EINVAL;
 56         }
 57 
 58         /* insn must be on a special executable page on ppc64.  This is
 59          * not explicitly required on ppc32 (right now), but it doesn't hurt */
 60         if (!ret) {
 61                 p->ainsn.insn = get_insn_slot();
 62                 if (!p->ainsn.insn)
 63                         ret = -ENOMEM;
 64         }
 65 
 66         if (!ret) {
 67                 memcpy(p->ainsn.insn, p->addr,
 68                                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 69                 p->opcode = *p->addr;
 70                 flush_icache_range((unsigned long)p->ainsn.insn,
 71                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
 72         }
 73 
 74         p->ainsn.boostable = 0;
 75         return ret;
 76 }
 77 
 78 void __kprobes arch_arm_kprobe(struct kprobe *p)
 79 {
 80         *p->addr = BREAKPOINT_INSTRUCTION;
 81         flush_icache_range((unsigned long) p->addr,
 82                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 83 }
 84 
 85 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 86 {
 87         *p->addr = p->opcode;
 88         flush_icache_range((unsigned long) p->addr,
 89                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 90 }
 91 
 92 void __kprobes arch_remove_kprobe(struct kprobe *p)
 93 {
 94         if (p->ainsn.insn) {
 95                 free_insn_slot(p->ainsn.insn, 0);
 96                 p->ainsn.insn = NULL;
 97         }
 98 }
 99 
100 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
101 {
102         enable_single_step(regs);
103 
104         /*
105          * On powerpc we should single step on the original
106          * instruction even if the probed insn is a trap
107          * variant as values in regs could play a part in
108          * if the trap is taken or not
109          */
110         regs->nip = (unsigned long)p->ainsn.insn;
111 }
112 
113 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
114 {
115         kcb->prev_kprobe.kp = kprobe_running();
116         kcb->prev_kprobe.status = kcb->kprobe_status;
117         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
118 }
119 
120 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
121 {
122         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
123         kcb->kprobe_status = kcb->prev_kprobe.status;
124         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
125 }
126 
127 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
128                                 struct kprobe_ctlblk *kcb)
129 {
130         __get_cpu_var(current_kprobe) = p;
131         kcb->kprobe_saved_msr = regs->msr;
132 }
133 
134 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
135                                       struct pt_regs *regs)
136 {
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 }
142 
143 static int __kprobes kprobe_handler(struct pt_regs *regs)
144 {
145         struct kprobe *p;
146         int ret = 0;
147         unsigned int *addr = (unsigned int *)regs->nip;
148         struct kprobe_ctlblk *kcb;
149 
150         /*
151          * We don't want to be preempted for the entire
152          * duration of kprobe processing
153          */
154         preempt_disable();
155         kcb = get_kprobe_ctlblk();
156 
157         /* Check we're not actually recursing */
158         if (kprobe_running()) {
159                 p = get_kprobe(addr);
160                 if (p) {
161                         kprobe_opcode_t insn = *p->ainsn.insn;
162                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
163                                         is_trap(insn)) {
164                                 /* Turn off 'trace' bits */
165                                 regs->msr &= ~MSR_SINGLESTEP;
166                                 regs->msr |= kcb->kprobe_saved_msr;
167                                 goto no_kprobe;
168                         }
169                         /* We have reentered the kprobe_handler(), since
170                          * another probe was hit while within the handler.
171                          * We here save the original kprobes variables and
172                          * just single step on the instruction of the new probe
173                          * without calling any user handlers.
174                          */
175                         save_previous_kprobe(kcb);
176                         set_current_kprobe(p, regs, kcb);
177                         kcb->kprobe_saved_msr = regs->msr;
178                         kprobes_inc_nmissed_count(p);
179                         prepare_singlestep(p, regs);
180                         kcb->kprobe_status = KPROBE_REENTER;
181                         return 1;
182                 } else {
183                         if (*addr != BREAKPOINT_INSTRUCTION) {
184                                 /* If trap variant, then it belongs not to us */
185                                 kprobe_opcode_t cur_insn = *addr;
186                                 if (is_trap(cur_insn))
187                                         goto no_kprobe;
188                                 /* The breakpoint instruction was removed by
189                                  * another cpu right after we hit, no further
190                                  * handling of this interrupt is appropriate
191                                  */
192                                 ret = 1;
193                                 goto no_kprobe;
194                         }
195                         p = __get_cpu_var(current_kprobe);
196                         if (p->break_handler && p->break_handler(p, regs)) {
197                                 goto ss_probe;
198                         }
199                 }
200                 goto no_kprobe;
201         }
202 
203         p = get_kprobe(addr);
204         if (!p) {
205                 if (*addr != BREAKPOINT_INSTRUCTION) {
206                         /*
207                          * PowerPC has multiple variants of the "trap"
208                          * instruction. If the current instruction is a
209                          * trap variant, it could belong to someone else
210                          */
211                         kprobe_opcode_t cur_insn = *addr;
212                         if (is_trap(cur_insn))
213                                 goto no_kprobe;
214                         /*
215                          * The breakpoint instruction was removed right
216                          * after we hit it.  Another cpu has removed
217                          * either a probepoint or a debugger breakpoint
218                          * at this address.  In either case, no further
219                          * handling of this interrupt is appropriate.
220                          */
221                         ret = 1;
222                 }
223                 /* Not one of ours: let kernel handle it */
224                 goto no_kprobe;
225         }
226 
227         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
228         set_current_kprobe(p, regs, kcb);
229         if (p->pre_handler && p->pre_handler(p, regs))
230                 /* handler has already set things up, so skip ss setup */
231                 return 1;
232 
233 ss_probe:
234         if (p->ainsn.boostable >= 0) {
235                 unsigned int insn = *p->ainsn.insn;
236 
237                 /* regs->nip is also adjusted if emulate_step returns 1 */
238                 ret = emulate_step(regs, insn);
239                 if (ret > 0) {
240                         /*
241                          * Once this instruction has been boosted
242                          * successfully, set the boostable flag
243                          */
244                         if (unlikely(p->ainsn.boostable == 0))
245                                 p->ainsn.boostable = 1;
246 
247                         if (p->post_handler)
248                                 p->post_handler(p, regs, 0);
249 
250                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
251                         reset_current_kprobe();
252                         preempt_enable_no_resched();
253                         return 1;
254                 } else if (ret < 0) {
255                         /*
256                          * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
257                          * So, we should never get here... but, its still
258                          * good to catch them, just in case...
259                          */
260                         printk("Can't step on instruction %x\n", insn);
261                         BUG();
262                 } else if (ret == 0)
263                         /* This instruction can't be boosted */
264                         p->ainsn.boostable = -1;
265         }
266         prepare_singlestep(p, regs);
267         kcb->kprobe_status = KPROBE_HIT_SS;
268         return 1;
269 
270 no_kprobe:
271         preempt_enable_no_resched();
272         return ret;
273 }
274 
275 /*
276  * Function return probe trampoline:
277  *      - init_kprobes() establishes a probepoint here
278  *      - When the probed function returns, this probe
279  *              causes the handlers to fire
280  */
281 static void __used kretprobe_trampoline_holder(void)
282 {
283         asm volatile(".global kretprobe_trampoline\n"
284                         "kretprobe_trampoline:\n"
285                         "nop\n");
286 }
287 
288 /*
289  * Called when the probe at kretprobe trampoline is hit
290  */
291 static int __kprobes trampoline_probe_handler(struct kprobe *p,
292                                                 struct pt_regs *regs)
293 {
294         struct kretprobe_instance *ri = NULL;
295         struct hlist_head *head, empty_rp;
296         struct hlist_node *tmp;
297         unsigned long flags, orig_ret_address = 0;
298         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
299 
300         INIT_HLIST_HEAD(&empty_rp);
301         kretprobe_hash_lock(current, &head, &flags);
302 
303         /*
304          * It is possible to have multiple instances associated with a given
305          * task either because an multiple functions in the call path
306          * have a return probe installed on them, and/or more than one return
307          * return probe was registered for a target function.
308          *
309          * We can handle this because:
310          *     - instances are always inserted at the head of the list
311          *     - when multiple return probes are registered for the same
312          *       function, the first instance's ret_addr will point to the
313          *       real return address, and all the rest will point to
314          *       kretprobe_trampoline
315          */
316         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
317                 if (ri->task != current)
318                         /* another task is sharing our hash bucket */
319                         continue;
320 
321                 if (ri->rp && ri->rp->handler)
322                         ri->rp->handler(ri, regs);
323 
324                 orig_ret_address = (unsigned long)ri->ret_addr;
325                 recycle_rp_inst(ri, &empty_rp);
326 
327                 if (orig_ret_address != trampoline_address)
328                         /*
329                          * This is the real return address. Any other
330                          * instances associated with this task are for
331                          * other calls deeper on the call stack
332                          */
333                         break;
334         }
335 
336         kretprobe_assert(ri, orig_ret_address, trampoline_address);
337         regs->nip = orig_ret_address;
338 
339         reset_current_kprobe();
340         kretprobe_hash_unlock(current, &flags);
341         preempt_enable_no_resched();
342 
343         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
344                 hlist_del(&ri->hlist);
345                 kfree(ri);
346         }
347         /*
348          * By returning a non-zero value, we are telling
349          * kprobe_handler() that we don't want the post_handler
350          * to run (and have re-enabled preemption)
351          */
352         return 1;
353 }
354 
355 /*
356  * Called after single-stepping.  p->addr is the address of the
357  * instruction whose first byte has been replaced by the "breakpoint"
358  * instruction.  To avoid the SMP problems that can occur when we
359  * temporarily put back the original opcode to single-step, we
360  * single-stepped a copy of the instruction.  The address of this
361  * copy is p->ainsn.insn.
362  */
363 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
364 {
365         struct kprobe *cur = kprobe_running();
366         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
367 
368         if (!cur)
369                 return 0;
370 
371         /* make sure we got here for instruction we have a kprobe on */
372         if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
373                 return 0;
374 
375         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
376                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
377                 cur->post_handler(cur, regs, 0);
378         }
379 
380         /* Adjust nip to after the single-stepped instruction */
381         regs->nip = (unsigned long)cur->addr + 4;
382         regs->msr |= kcb->kprobe_saved_msr;
383 
384         /*Restore back the original saved kprobes variables and continue. */
385         if (kcb->kprobe_status == KPROBE_REENTER) {
386                 restore_previous_kprobe(kcb);
387                 goto out;
388         }
389         reset_current_kprobe();
390 out:
391         preempt_enable_no_resched();
392 
393         /*
394          * if somebody else is singlestepping across a probe point, msr
395          * will have DE/SE set, in which case, continue the remaining processing
396          * of do_debug, as if this is not a probe hit.
397          */
398         if (regs->msr & MSR_SINGLESTEP)
399                 return 0;
400 
401         return 1;
402 }
403 
404 int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
405 {
406         struct kprobe *cur = kprobe_running();
407         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
408         const struct exception_table_entry *entry;
409 
410         switch(kcb->kprobe_status) {
411         case KPROBE_HIT_SS:
412         case KPROBE_REENTER:
413                 /*
414                  * We are here because the instruction being single
415                  * stepped caused a page fault. We reset the current
416                  * kprobe and the nip points back to the probe address
417                  * and allow the page fault handler to continue as a
418                  * normal page fault.
419                  */
420                 regs->nip = (unsigned long)cur->addr;
421                 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
422                 regs->msr |= kcb->kprobe_saved_msr;
423                 if (kcb->kprobe_status == KPROBE_REENTER)
424                         restore_previous_kprobe(kcb);
425                 else
426                         reset_current_kprobe();
427                 preempt_enable_no_resched();
428                 break;
429         case KPROBE_HIT_ACTIVE:
430         case KPROBE_HIT_SSDONE:
431                 /*
432                  * We increment the nmissed count for accounting,
433                  * we can also use npre/npostfault count for accounting
434                  * these specific fault cases.
435                  */
436                 kprobes_inc_nmissed_count(cur);
437 
438                 /*
439                  * We come here because instructions in the pre/post
440                  * handler caused the page_fault, this could happen
441                  * if handler tries to access user space by
442                  * copy_from_user(), get_user() etc. Let the
443                  * user-specified handler try to fix it first.
444                  */
445                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
446                         return 1;
447 
448                 /*
449                  * In case the user-specified fault handler returned
450                  * zero, try to fix up.
451                  */
452                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
453                         regs->nip = entry->fixup;
454                         return 1;
455                 }
456 
457                 /*
458                  * fixup_exception() could not handle it,
459                  * Let do_page_fault() fix it.
460                  */
461                 break;
462         default:
463                 break;
464         }
465         return 0;
466 }
467 
468 /*
469  * Wrapper routine to for handling exceptions.
470  */
471 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
472                                        unsigned long val, void *data)
473 {
474         struct die_args *args = (struct die_args *)data;
475         int ret = NOTIFY_DONE;
476 
477         if (args->regs && user_mode(args->regs))
478                 return ret;
479 
480         switch (val) {
481         case DIE_BPT:
482                 if (kprobe_handler(args->regs))
483                         ret = NOTIFY_STOP;
484                 break;
485         case DIE_SSTEP:
486                 if (post_kprobe_handler(args->regs))
487                         ret = NOTIFY_STOP;
488                 break;
489         default:
490                 break;
491         }
492         return ret;
493 }
494 
495 unsigned long arch_deref_entry_point(void *entry)
496 {
497         return ppc_global_function_entry(entry);
498 }
499 
500 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
501 {
502         struct jprobe *jp = container_of(p, struct jprobe, kp);
503         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
504 
505         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
506 
507         /* setup return addr to the jprobe handler routine */
508         regs->nip = arch_deref_entry_point(jp->entry);
509 #ifdef CONFIG_PPC64
510 #if defined(_CALL_ELF) && _CALL_ELF == 2
511         regs->gpr[12] = (unsigned long)jp->entry;
512 #else
513         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
514 #endif
515 #endif
516 
517         /*
518          * jprobes use jprobe_return() which skips the normal return
519          * path of the function, and this messes up the accounting of the
520          * function graph tracer.
521          *
522          * Pause function graph tracing while performing the jprobe function.
523          */
524         pause_graph_tracing();
525 
526         return 1;
527 }
528 
529 void __used __kprobes jprobe_return(void)
530 {
531         asm volatile("trap" ::: "memory");
532 }
533 
534 static void __used __kprobes jprobe_return_end(void)
535 {
536 };
537 
538 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
539 {
540         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
541 
542         /*
543          * FIXME - we should ideally be validating that we got here 'cos
544          * of the "trap" in jprobe_return() above, before restoring the
545          * saved regs...
546          */
547         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
548         /* It's OK to start function graph tracing again */
549         unpause_graph_tracing();
550         preempt_enable_no_resched();
551         return 1;
552 }
553 
554 static struct kprobe trampoline_p = {
555         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
556         .pre_handler = trampoline_probe_handler
557 };
558 
559 int __init arch_init_kprobes(void)
560 {
561         return register_kprobe(&trampoline_p);
562 }
563 
564 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
565 {
566         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
567                 return 1;
568 
569         return 0;
570 }
571 

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