1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Kernel Probes (KProbes)
4 *
5 * Copyright (C) IBM Corporation, 2002, 2004
6 *
7 * 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
8 * Probes initial implementation ( includes contributions from
9 * Rusty Russell).
10 * 2004-July Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
11 * interface to access function arguments.
12 * 2004-Nov Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
13 * for PPC64
14 */
15
16 #include <linux/kprobes.h>
17 #include <linux/ptrace.h>
18 #include <linux/preempt.h>
19 #include <linux/extable.h>
20 #include <linux/kdebug.h>
21 #include <linux/slab.h>
22 #include <asm/code-patching.h>
23 #include <asm/cacheflush.h>
24 #include <asm/sstep.h>
25 #include <asm/sections.h>
26 #include <linux/uaccess.h>
27
28 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
29 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
30
31 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
32
33 bool arch_within_kprobe_blacklist(unsigned long addr)
34 {
35 return (addr >= (unsigned long)__kprobes_text_start &&
36 addr < (unsigned long)__kprobes_text_end) ||
37 (addr >= (unsigned long)_stext &&
38 addr < (unsigned long)__head_end);
39 }
40
41 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
42 {
43 kprobe_opcode_t *addr = NULL;
44
45 #ifdef PPC64_ELF_ABI_v2
46 /* PPC64 ABIv2 needs local entry point */
47 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
48 if (addr && !offset) {
49 #ifdef CONFIG_KPROBES_ON_FTRACE
50 unsigned long faddr;
51 /*
52 * Per livepatch.h, ftrace location is always within the first
53 * 16 bytes of a function on powerpc with -mprofile-kernel.
54 */
55 faddr = ftrace_location_range((unsigned long)addr,
56 (unsigned long)addr + 16);
57 if (faddr)
58 addr = (kprobe_opcode_t *)faddr;
59 else
60 #endif
61 addr = (kprobe_opcode_t *)ppc_function_entry(addr);
62 }
63 #elif defined(PPC64_ELF_ABI_v1)
64 /*
65 * 64bit powerpc ABIv1 uses function descriptors:
66 * - Check for the dot variant of the symbol first.
67 * - If that fails, try looking up the symbol provided.
68 *
69 * This ensures we always get to the actual symbol and not
70 * the descriptor.
71 *
72 * Also handle <module:symbol> format.
73 */
74 char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
75 bool dot_appended = false;
76 const char *c;
77 ssize_t ret = 0;
78 int len = 0;
79
80 if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
81 c++;
82 len = c - name;
83 memcpy(dot_name, name, len);
84 } else
85 c = name;
86
87 if (*c != '\0' && *c != '.') {
88 dot_name[len++] = '.';
89 dot_appended = true;
90 }
91 ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
92 if (ret > 0)
93 addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
94
95 /* Fallback to the original non-dot symbol lookup */
96 if (!addr && dot_appended)
97 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
98 #else
99 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
100 #endif
101
102 return addr;
103 }
104
105 int arch_prepare_kprobe(struct kprobe *p)
106 {
107 int ret = 0;
108 kprobe_opcode_t insn = *p->addr;
109
110 if ((unsigned long)p->addr & 0x03) {
111 printk("Attempt to register kprobe at an unaligned address\n");
112 ret = -EINVAL;
113 } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
114 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
115 ret = -EINVAL;
116 }
117
118 /* insn must be on a special executable page on ppc64. This is
119 * not explicitly required on ppc32 (right now), but it doesn't hurt */
120 if (!ret) {
121 p->ainsn.insn = get_insn_slot();
122 if (!p->ainsn.insn)
123 ret = -ENOMEM;
124 }
125
126 if (!ret) {
127 memcpy(p->ainsn.insn, p->addr,
128 MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
129 p->opcode = *p->addr;
130 flush_icache_range((unsigned long)p->ainsn.insn,
131 (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
132 }
133
134 p->ainsn.boostable = 0;
135 return ret;
136 }
137 NOKPROBE_SYMBOL(arch_prepare_kprobe);
138
139 void arch_arm_kprobe(struct kprobe *p)
140 {
141 patch_instruction(p->addr, BREAKPOINT_INSTRUCTION);
142 }
143 NOKPROBE_SYMBOL(arch_arm_kprobe);
144
145 void arch_disarm_kprobe(struct kprobe *p)
146 {
147 patch_instruction(p->addr, p->opcode);
148 }
149 NOKPROBE_SYMBOL(arch_disarm_kprobe);
150
151 void arch_remove_kprobe(struct kprobe *p)
152 {
153 if (p->ainsn.insn) {
154 free_insn_slot(p->ainsn.insn, 0);
155 p->ainsn.insn = NULL;
156 }
157 }
158 NOKPROBE_SYMBOL(arch_remove_kprobe);
159
160 static nokprobe_inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
161 {
162 enable_single_step(regs);
163
164 /*
165 * On powerpc we should single step on the original
166 * instruction even if the probed insn is a trap
167 * variant as values in regs could play a part in
168 * if the trap is taken or not
169 */
170 regs->nip = (unsigned long)p->ainsn.insn;
171 }
172
173 static nokprobe_inline void save_previous_kprobe(struct kprobe_ctlblk *kcb)
174 {
175 kcb->prev_kprobe.kp = kprobe_running();
176 kcb->prev_kprobe.status = kcb->kprobe_status;
177 kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
178 }
179
180 static nokprobe_inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
181 {
182 __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
183 kcb->kprobe_status = kcb->prev_kprobe.status;
184 kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
185 }
186
187 static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
188 struct kprobe_ctlblk *kcb)
189 {
190 __this_cpu_write(current_kprobe, p);
191 kcb->kprobe_saved_msr = regs->msr;
192 }
193
194 bool arch_kprobe_on_func_entry(unsigned long offset)
195 {
196 #ifdef PPC64_ELF_ABI_v2
197 #ifdef CONFIG_KPROBES_ON_FTRACE
198 return offset <= 16;
199 #else
200 return offset <= 8;
201 #endif
202 #else
203 return !offset;
204 #endif
205 }
206
207 void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
208 {
209 ri->ret_addr = (kprobe_opcode_t *)regs->link;
210
211 /* Replace the return addr with trampoline addr */
212 regs->link = (unsigned long)kretprobe_trampoline;
213 }
214 NOKPROBE_SYMBOL(arch_prepare_kretprobe);
215
216 static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
217 {
218 int ret;
219 unsigned int insn = *p->ainsn.insn;
220
221 /* regs->nip is also adjusted if emulate_step returns 1 */
222 ret = emulate_step(regs, insn);
223 if (ret > 0) {
224 /*
225 * Once this instruction has been boosted
226 * successfully, set the boostable flag
227 */
228 if (unlikely(p->ainsn.boostable == 0))
229 p->ainsn.boostable = 1;
230 } else if (ret < 0) {
231 /*
232 * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
233 * So, we should never get here... but, its still
234 * good to catch them, just in case...
235 */
236 printk("Can't step on instruction %x\n", insn);
237 BUG();
238 } else {
239 /*
240 * If we haven't previously emulated this instruction, then it
241 * can't be boosted. Note it down so we don't try to do so again.
242 *
243 * If, however, we had emulated this instruction in the past,
244 * then this is just an error with the current run (for
245 * instance, exceptions due to a load/store). We return 0 so
246 * that this is now single-stepped, but continue to try
247 * emulating it in subsequent probe hits.
248 */
249 if (unlikely(p->ainsn.boostable != 1))
250 p->ainsn.boostable = -1;
251 }
252
253 return ret;
254 }
255 NOKPROBE_SYMBOL(try_to_emulate);
256
257 int kprobe_handler(struct pt_regs *regs)
258 {
259 struct kprobe *p;
260 int ret = 0;
261 unsigned int *addr = (unsigned int *)regs->nip;
262 struct kprobe_ctlblk *kcb;
263
264 if (user_mode(regs))
265 return 0;
266
267 if (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR))
268 return 0;
269
270 /*
271 * We don't want to be preempted for the entire
272 * duration of kprobe processing
273 */
274 preempt_disable();
275 kcb = get_kprobe_ctlblk();
276
277 /* Check we're not actually recursing */
278 if (kprobe_running()) {
279 p = get_kprobe(addr);
280 if (p) {
281 kprobe_opcode_t insn = *p->ainsn.insn;
282 if (kcb->kprobe_status == KPROBE_HIT_SS &&
283 is_trap(insn)) {
284 /* Turn off 'trace' bits */
285 regs->msr &= ~MSR_SINGLESTEP;
286 regs->msr |= kcb->kprobe_saved_msr;
287 goto no_kprobe;
288 }
289 /* We have reentered the kprobe_handler(), since
290 * another probe was hit while within the handler.
291 * We here save the original kprobes variables and
292 * just single step on the instruction of the new probe
293 * without calling any user handlers.
294 */
295 save_previous_kprobe(kcb);
296 set_current_kprobe(p, regs, kcb);
297 kprobes_inc_nmissed_count(p);
298 kcb->kprobe_status = KPROBE_REENTER;
299 if (p->ainsn.boostable >= 0) {
300 ret = try_to_emulate(p, regs);
301
302 if (ret > 0) {
303 restore_previous_kprobe(kcb);
304 preempt_enable_no_resched();
305 return 1;
306 }
307 }
308 prepare_singlestep(p, regs);
309 return 1;
310 } else if (*addr != BREAKPOINT_INSTRUCTION) {
311 /* If trap variant, then it belongs not to us */
312 kprobe_opcode_t cur_insn = *addr;
313
314 if (is_trap(cur_insn))
315 goto no_kprobe;
316 /* The breakpoint instruction was removed by
317 * another cpu right after we hit, no further
318 * handling of this interrupt is appropriate
319 */
320 ret = 1;
321 }
322 goto no_kprobe;
323 }
324
325 p = get_kprobe(addr);
326 if (!p) {
327 if (*addr != BREAKPOINT_INSTRUCTION) {
328 /*
329 * PowerPC has multiple variants of the "trap"
330 * instruction. If the current instruction is a
331 * trap variant, it could belong to someone else
332 */
333 kprobe_opcode_t cur_insn = *addr;
334 if (is_trap(cur_insn))
335 goto no_kprobe;
336 /*
337 * The breakpoint instruction was removed right
338 * after we hit it. Another cpu has removed
339 * either a probepoint or a debugger breakpoint
340 * at this address. In either case, no further
341 * handling of this interrupt is appropriate.
342 */
343 ret = 1;
344 }
345 /* Not one of ours: let kernel handle it */
346 goto no_kprobe;
347 }
348
349 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
350 set_current_kprobe(p, regs, kcb);
351 if (p->pre_handler && p->pre_handler(p, regs)) {
352 /* handler changed execution path, so skip ss setup */
353 reset_current_kprobe();
354 preempt_enable_no_resched();
355 return 1;
356 }
357
358 if (p->ainsn.boostable >= 0) {
359 ret = try_to_emulate(p, regs);
360
361 if (ret > 0) {
362 if (p->post_handler)
363 p->post_handler(p, regs, 0);
364
365 kcb->kprobe_status = KPROBE_HIT_SSDONE;
366 reset_current_kprobe();
367 preempt_enable_no_resched();
368 return 1;
369 }
370 }
371 prepare_singlestep(p, regs);
372 kcb->kprobe_status = KPROBE_HIT_SS;
373 return 1;
374
375 no_kprobe:
376 preempt_enable_no_resched();
377 return ret;
378 }
379 NOKPROBE_SYMBOL(kprobe_handler);
380
381 /*
382 * Function return probe trampoline:
383 * - init_kprobes() establishes a probepoint here
384 * - When the probed function returns, this probe
385 * causes the handlers to fire
386 */
387 asm(".global kretprobe_trampoline\n"
388 ".type kretprobe_trampoline, @function\n"
389 "kretprobe_trampoline:\n"
390 "nop\n"
391 "blr\n"
392 ".size kretprobe_trampoline, .-kretprobe_trampoline\n");
393
394 /*
395 * Called when the probe at kretprobe trampoline is hit
396 */
397 static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
398 {
399 struct kretprobe_instance *ri = NULL;
400 struct hlist_head *head, empty_rp;
401 struct hlist_node *tmp;
402 unsigned long flags, orig_ret_address = 0;
403 unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
404
405 INIT_HLIST_HEAD(&empty_rp);
406 kretprobe_hash_lock(current, &head, &flags);
407
408 /*
409 * It is possible to have multiple instances associated with a given
410 * task either because an multiple functions in the call path
411 * have a return probe installed on them, and/or more than one return
412 * return probe was registered for a target function.
413 *
414 * We can handle this because:
415 * - instances are always inserted at the head of the list
416 * - when multiple return probes are registered for the same
417 * function, the first instance's ret_addr will point to the
418 * real return address, and all the rest will point to
419 * kretprobe_trampoline
420 */
421 hlist_for_each_entry_safe(ri, tmp, head, hlist) {
422 if (ri->task != current)
423 /* another task is sharing our hash bucket */
424 continue;
425
426 if (ri->rp && ri->rp->handler)
427 ri->rp->handler(ri, regs);
428
429 orig_ret_address = (unsigned long)ri->ret_addr;
430 recycle_rp_inst(ri, &empty_rp);
431
432 if (orig_ret_address != trampoline_address)
433 /*
434 * This is the real return address. Any other
435 * instances associated with this task are for
436 * other calls deeper on the call stack
437 */
438 break;
439 }
440
441 kretprobe_assert(ri, orig_ret_address, trampoline_address);
442
443 /*
444 * We get here through one of two paths:
445 * 1. by taking a trap -> kprobe_handler() -> here
446 * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
447 *
448 * When going back through (1), we need regs->nip to be setup properly
449 * as it is used to determine the return address from the trap.
450 * For (2), since nip is not honoured with optprobes, we instead setup
451 * the link register properly so that the subsequent 'blr' in
452 * kretprobe_trampoline jumps back to the right instruction.
453 *
454 * For nip, we should set the address to the previous instruction since
455 * we end up emulating it in kprobe_handler(), which increments the nip
456 * again.
457 */
458 regs->nip = orig_ret_address - 4;
459 regs->link = orig_ret_address;
460
461 kretprobe_hash_unlock(current, &flags);
462
463 hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
464 hlist_del(&ri->hlist);
465 kfree(ri);
466 }
467
468 return 0;
469 }
470 NOKPROBE_SYMBOL(trampoline_probe_handler);
471
472 /*
473 * Called after single-stepping. p->addr is the address of the
474 * instruction whose first byte has been replaced by the "breakpoint"
475 * instruction. To avoid the SMP problems that can occur when we
476 * temporarily put back the original opcode to single-step, we
477 * single-stepped a copy of the instruction. The address of this
478 * copy is p->ainsn.insn.
479 */
480 int kprobe_post_handler(struct pt_regs *regs)
481 {
482 struct kprobe *cur = kprobe_running();
483 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
484
485 if (!cur || user_mode(regs))
486 return 0;
487
488 /* make sure we got here for instruction we have a kprobe on */
489 if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
490 return 0;
491
492 if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
493 kcb->kprobe_status = KPROBE_HIT_SSDONE;
494 cur->post_handler(cur, regs, 0);
495 }
496
497 /* Adjust nip to after the single-stepped instruction */
498 regs->nip = (unsigned long)cur->addr + 4;
499 regs->msr |= kcb->kprobe_saved_msr;
500
501 /*Restore back the original saved kprobes variables and continue. */
502 if (kcb->kprobe_status == KPROBE_REENTER) {
503 restore_previous_kprobe(kcb);
504 goto out;
505 }
506 reset_current_kprobe();
507 out:
508 preempt_enable_no_resched();
509
510 /*
511 * if somebody else is singlestepping across a probe point, msr
512 * will have DE/SE set, in which case, continue the remaining processing
513 * of do_debug, as if this is not a probe hit.
514 */
515 if (regs->msr & MSR_SINGLESTEP)
516 return 0;
517
518 return 1;
519 }
520 NOKPROBE_SYMBOL(kprobe_post_handler);
521
522 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
523 {
524 struct kprobe *cur = kprobe_running();
525 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
526 const struct exception_table_entry *entry;
527
528 switch(kcb->kprobe_status) {
529 case KPROBE_HIT_SS:
530 case KPROBE_REENTER:
531 /*
532 * We are here because the instruction being single
533 * stepped caused a page fault. We reset the current
534 * kprobe and the nip points back to the probe address
535 * and allow the page fault handler to continue as a
536 * normal page fault.
537 */
538 regs->nip = (unsigned long)cur->addr;
539 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
540 regs->msr |= kcb->kprobe_saved_msr;
541 if (kcb->kprobe_status == KPROBE_REENTER)
542 restore_previous_kprobe(kcb);
543 else
544 reset_current_kprobe();
545 preempt_enable_no_resched();
546 break;
547 case KPROBE_HIT_ACTIVE:
548 case KPROBE_HIT_SSDONE:
549 /*
550 * We increment the nmissed count for accounting,
551 * we can also use npre/npostfault count for accounting
552 * these specific fault cases.
553 */
554 kprobes_inc_nmissed_count(cur);
555
556 /*
557 * We come here because instructions in the pre/post
558 * handler caused the page_fault, this could happen
559 * if handler tries to access user space by
560 * copy_from_user(), get_user() etc. Let the
561 * user-specified handler try to fix it first.
562 */
563 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
564 return 1;
565
566 /*
567 * In case the user-specified fault handler returned
568 * zero, try to fix up.
569 */
570 if ((entry = search_exception_tables(regs->nip)) != NULL) {
571 regs->nip = extable_fixup(entry);
572 return 1;
573 }
574
575 /*
576 * fixup_exception() could not handle it,
577 * Let do_page_fault() fix it.
578 */
579 break;
580 default:
581 break;
582 }
583 return 0;
584 }
585 NOKPROBE_SYMBOL(kprobe_fault_handler);
586
587 unsigned long arch_deref_entry_point(void *entry)
588 {
589 #ifdef PPC64_ELF_ABI_v1
590 if (!kernel_text_address((unsigned long)entry))
591 return ppc_global_function_entry(entry);
592 else
593 #endif
594 return (unsigned long)entry;
595 }
596 NOKPROBE_SYMBOL(arch_deref_entry_point);
597
598 static struct kprobe trampoline_p = {
599 .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
600 .pre_handler = trampoline_probe_handler
601 };
602
603 int __init arch_init_kprobes(void)
604 {
605 return register_kprobe(&trampoline_p);
606 }
607
608 int arch_trampoline_kprobe(struct kprobe *p)
609 {
610 if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
611 return 1;
612
613 return 0;
614 }
615 NOKPROBE_SYMBOL(arch_trampoline_kprobe);