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 <linux/set_memory.h>
23 #include <linux/execmem.h>
24 #include <asm/code-patching.h>
25 #include <asm/cacheflush.h>
26 #include <asm/sstep.h>
27 #include <asm/sections.h>
28 #include <asm/inst.h>
29 #include <linux/uaccess.h>
30
31 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
32 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
33
34 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
35
36 bool arch_within_kprobe_blacklist(unsigned long addr)
37 {
38 return (addr >= (unsigned long)__kprobes_text_start &&
39 addr < (unsigned long)__kprobes_text_end) ||
40 (addr >= (unsigned long)_stext &&
41 addr < (unsigned long)__head_end);
42 }
43
44 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
45 {
46 kprobe_opcode_t *addr = NULL;
47
48 #ifdef CONFIG_PPC64_ELF_ABI_V2
49 /* PPC64 ABIv2 needs local entry point */
50 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
51 if (addr && !offset) {
52 #ifdef CONFIG_KPROBES_ON_FTRACE
53 unsigned long faddr;
54 /*
55 * Per livepatch.h, ftrace location is always within the first
56 * 16 bytes of a function on powerpc with -mprofile-kernel.
57 */
58 faddr = ftrace_location_range((unsigned long)addr,
59 (unsigned long)addr + 16);
60 if (faddr)
61 addr = (kprobe_opcode_t *)faddr;
62 else
63 #endif
64 addr = (kprobe_opcode_t *)ppc_function_entry(addr);
65 }
66 #elif defined(CONFIG_PPC64_ELF_ABI_V1)
67 /*
68 * 64bit powerpc ABIv1 uses function descriptors:
69 * - Check for the dot variant of the symbol first.
70 * - If that fails, try looking up the symbol provided.
71 *
72 * This ensures we always get to the actual symbol and not
73 * the descriptor.
74 *
75 * Also handle <module:symbol> format.
76 */
77 char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
78 bool dot_appended = false;
79 const char *c;
80 ssize_t ret = 0;
81 int len = 0;
82
83 if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
84 c++;
85 len = c - name;
86 memcpy(dot_name, name, len);
87 } else
88 c = name;
89
90 if (*c != '\0' && *c != '.') {
91 dot_name[len++] = '.';
92 dot_appended = true;
93 }
94 ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
95 if (ret > 0)
96 addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
97
98 /* Fallback to the original non-dot symbol lookup */
99 if (!addr && dot_appended)
100 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
101 #else
102 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
103 #endif
104
105 return addr;
106 }
107
108 static bool arch_kprobe_on_func_entry(unsigned long offset)
109 {
110 #ifdef CONFIG_PPC64_ELF_ABI_V2
111 #ifdef CONFIG_KPROBES_ON_FTRACE
112 return offset <= 16;
113 #else
114 return offset <= 8;
115 #endif
116 #else
117 return !offset;
118 #endif
119 }
120
121 /* XXX try and fold the magic of kprobe_lookup_name() in this */
122 kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
123 bool *on_func_entry)
124 {
125 *on_func_entry = arch_kprobe_on_func_entry(offset);
126 return (kprobe_opcode_t *)(addr + offset);
127 }
128
129 int arch_prepare_kprobe(struct kprobe *p)
130 {
131 int ret = 0;
132 struct kprobe *prev;
133 ppc_inst_t insn = ppc_inst_read(p->addr);
134
135 if ((unsigned long)p->addr & 0x03) {
136 printk("Attempt to register kprobe at an unaligned address\n");
137 ret = -EINVAL;
138 } else if (!can_single_step(ppc_inst_val(insn))) {
139 printk("Cannot register a kprobe on instructions that can't be single stepped\n");
140 ret = -EINVAL;
141 } else if ((unsigned long)p->addr & ~PAGE_MASK &&
142 ppc_inst_prefixed(ppc_inst_read(p->addr - 1))) {
143 printk("Cannot register a kprobe on the second word of prefixed instruction\n");
144 ret = -EINVAL;
145 }
146 prev = get_kprobe(p->addr - 1);
147
148 /*
149 * When prev is a ftrace-based kprobe, we don't have an insn, and it
150 * doesn't probe for prefixed instruction.
151 */
152 if (prev && !kprobe_ftrace(prev) &&
153 ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) {
154 printk("Cannot register a kprobe on the second word of prefixed instruction\n");
155 ret = -EINVAL;
156 }
157
158 /* insn must be on a special executable page on ppc64. This is
159 * not explicitly required on ppc32 (right now), but it doesn't hurt */
160 if (!ret) {
161 p->ainsn.insn = get_insn_slot();
162 if (!p->ainsn.insn)
163 ret = -ENOMEM;
164 }
165
166 if (!ret) {
167 patch_instruction(p->ainsn.insn, insn);
168 p->opcode = ppc_inst_val(insn);
169 }
170
171 p->ainsn.boostable = 0;
172 return ret;
173 }
174 NOKPROBE_SYMBOL(arch_prepare_kprobe);
175
176 void arch_arm_kprobe(struct kprobe *p)
177 {
178 WARN_ON_ONCE(patch_instruction(p->addr, ppc_inst(BREAKPOINT_INSTRUCTION)));
179 }
180 NOKPROBE_SYMBOL(arch_arm_kprobe);
181
182 void arch_disarm_kprobe(struct kprobe *p)
183 {
184 WARN_ON_ONCE(patch_instruction(p->addr, ppc_inst(p->opcode)));
185 }
186 NOKPROBE_SYMBOL(arch_disarm_kprobe);
187
188 void arch_remove_kprobe(struct kprobe *p)
189 {
190 if (p->ainsn.insn) {
191 free_insn_slot(p->ainsn.insn, 0);
192 p->ainsn.insn = NULL;
193 }
194 }
195 NOKPROBE_SYMBOL(arch_remove_kprobe);
196
197 static nokprobe_inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
198 {
199 enable_single_step(regs);
200
201 /*
202 * On powerpc we should single step on the original
203 * instruction even if the probed insn is a trap
204 * variant as values in regs could play a part in
205 * if the trap is taken or not
206 */
207 regs_set_return_ip(regs, (unsigned long)p->ainsn.insn);
208 }
209
210 static nokprobe_inline void save_previous_kprobe(struct kprobe_ctlblk *kcb)
211 {
212 kcb->prev_kprobe.kp = kprobe_running();
213 kcb->prev_kprobe.status = kcb->kprobe_status;
214 kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
215 }
216
217 static nokprobe_inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
218 {
219 __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
220 kcb->kprobe_status = kcb->prev_kprobe.status;
221 kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
222 }
223
224 static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
225 struct kprobe_ctlblk *kcb)
226 {
227 __this_cpu_write(current_kprobe, p);
228 kcb->kprobe_saved_msr = regs->msr;
229 }
230
231 void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
232 {
233 ri->ret_addr = (kprobe_opcode_t *)regs->link;
234 ri->fp = NULL;
235
236 /* Replace the return addr with trampoline addr */
237 regs->link = (unsigned long)__kretprobe_trampoline;
238 }
239 NOKPROBE_SYMBOL(arch_prepare_kretprobe);
240
241 static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
242 {
243 int ret;
244 ppc_inst_t insn = ppc_inst_read(p->ainsn.insn);
245
246 /* regs->nip is also adjusted if emulate_step returns 1 */
247 ret = emulate_step(regs, insn);
248 if (ret > 0) {
249 /*
250 * Once this instruction has been boosted
251 * successfully, set the boostable flag
252 */
253 if (unlikely(p->ainsn.boostable == 0))
254 p->ainsn.boostable = 1;
255 } else if (ret < 0) {
256 /*
257 * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
258 * So, we should never get here... but, its still
259 * good to catch them, just in case...
260 */
261 printk("Can't step on instruction %08lx\n", ppc_inst_as_ulong(insn));
262 BUG();
263 } else {
264 /*
265 * If we haven't previously emulated this instruction, then it
266 * can't be boosted. Note it down so we don't try to do so again.
267 *
268 * If, however, we had emulated this instruction in the past,
269 * then this is just an error with the current run (for
270 * instance, exceptions due to a load/store). We return 0 so
271 * that this is now single-stepped, but continue to try
272 * emulating it in subsequent probe hits.
273 */
274 if (unlikely(p->ainsn.boostable != 1))
275 p->ainsn.boostable = -1;
276 }
277
278 return ret;
279 }
280 NOKPROBE_SYMBOL(try_to_emulate);
281
282 int kprobe_handler(struct pt_regs *regs)
283 {
284 struct kprobe *p;
285 int ret = 0;
286 unsigned int *addr = (unsigned int *)regs->nip;
287 struct kprobe_ctlblk *kcb;
288
289 if (user_mode(regs))
290 return 0;
291
292 if (!IS_ENABLED(CONFIG_BOOKE) &&
293 (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR)))
294 return 0;
295
296 /*
297 * We don't want to be preempted for the entire
298 * duration of kprobe processing
299 */
300 preempt_disable();
301 kcb = get_kprobe_ctlblk();
302
303 p = get_kprobe(addr);
304 if (!p) {
305 unsigned int instr;
306
307 if (get_kernel_nofault(instr, addr))
308 goto no_kprobe;
309
310 if (instr != BREAKPOINT_INSTRUCTION) {
311 /*
312 * PowerPC has multiple variants of the "trap"
313 * instruction. If the current instruction is a
314 * trap variant, it could belong to someone else
315 */
316 if (is_trap(instr))
317 goto no_kprobe;
318 /*
319 * The breakpoint instruction was removed right
320 * after we hit it. Another cpu has removed
321 * either a probepoint or a debugger breakpoint
322 * at this address. In either case, no further
323 * handling of this interrupt is appropriate.
324 */
325 ret = 1;
326 }
327 /* Not one of ours: let kernel handle it */
328 goto no_kprobe;
329 }
330
331 /* Check we're not actually recursing */
332 if (kprobe_running()) {
333 kprobe_opcode_t insn = *p->ainsn.insn;
334 if (kcb->kprobe_status == KPROBE_HIT_SS && is_trap(insn)) {
335 /* Turn off 'trace' bits */
336 regs_set_return_msr(regs,
337 (regs->msr & ~MSR_SINGLESTEP) |
338 kcb->kprobe_saved_msr);
339 goto no_kprobe;
340 }
341
342 /*
343 * We have reentered the kprobe_handler(), since another probe
344 * was hit while within the handler. We here save the original
345 * kprobes variables and just single step on the instruction of
346 * the new probe without calling any user handlers.
347 */
348 save_previous_kprobe(kcb);
349 set_current_kprobe(p, regs, kcb);
350 kprobes_inc_nmissed_count(p);
351 kcb->kprobe_status = KPROBE_REENTER;
352 if (p->ainsn.boostable >= 0) {
353 ret = try_to_emulate(p, regs);
354
355 if (ret > 0) {
356 restore_previous_kprobe(kcb);
357 preempt_enable();
358 return 1;
359 }
360 }
361 prepare_singlestep(p, regs);
362 return 1;
363 }
364
365 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
366 set_current_kprobe(p, regs, kcb);
367 if (p->pre_handler && p->pre_handler(p, regs)) {
368 /* handler changed execution path, so skip ss setup */
369 reset_current_kprobe();
370 preempt_enable();
371 return 1;
372 }
373
374 if (p->ainsn.boostable >= 0) {
375 ret = try_to_emulate(p, regs);
376
377 if (ret > 0) {
378 if (p->post_handler)
379 p->post_handler(p, regs, 0);
380
381 kcb->kprobe_status = KPROBE_HIT_SSDONE;
382 reset_current_kprobe();
383 preempt_enable();
384 return 1;
385 }
386 }
387 prepare_singlestep(p, regs);
388 kcb->kprobe_status = KPROBE_HIT_SS;
389 return 1;
390
391 no_kprobe:
392 preempt_enable();
393 return ret;
394 }
395 NOKPROBE_SYMBOL(kprobe_handler);
396
397 /*
398 * Function return probe trampoline:
399 * - init_kprobes() establishes a probepoint here
400 * - When the probed function returns, this probe
401 * causes the handlers to fire
402 */
403 asm(".global __kretprobe_trampoline\n"
404 ".type __kretprobe_trampoline, @function\n"
405 "__kretprobe_trampoline:\n"
406 "nop\n"
407 "blr\n"
408 ".size __kretprobe_trampoline, .-__kretprobe_trampoline\n");
409
410 /*
411 * Called when the probe at kretprobe trampoline is hit
412 */
413 static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
414 {
415 unsigned long orig_ret_address;
416
417 orig_ret_address = __kretprobe_trampoline_handler(regs, NULL);
418 /*
419 * We get here through one of two paths:
420 * 1. by taking a trap -> kprobe_handler() -> here
421 * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
422 *
423 * When going back through (1), we need regs->nip to be setup properly
424 * as it is used to determine the return address from the trap.
425 * For (2), since nip is not honoured with optprobes, we instead setup
426 * the link register properly so that the subsequent 'blr' in
427 * __kretprobe_trampoline jumps back to the right instruction.
428 *
429 * For nip, we should set the address to the previous instruction since
430 * we end up emulating it in kprobe_handler(), which increments the nip
431 * again.
432 */
433 regs_set_return_ip(regs, orig_ret_address - 4);
434 regs->link = orig_ret_address;
435
436 return 0;
437 }
438 NOKPROBE_SYMBOL(trampoline_probe_handler);
439
440 /*
441 * Called after single-stepping. p->addr is the address of the
442 * instruction whose first byte has been replaced by the "breakpoint"
443 * instruction. To avoid the SMP problems that can occur when we
444 * temporarily put back the original opcode to single-step, we
445 * single-stepped a copy of the instruction. The address of this
446 * copy is p->ainsn.insn.
447 */
448 int kprobe_post_handler(struct pt_regs *regs)
449 {
450 int len;
451 struct kprobe *cur = kprobe_running();
452 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
453
454 if (!cur || user_mode(regs))
455 return 0;
456
457 len = ppc_inst_len(ppc_inst_read(cur->ainsn.insn));
458 /* make sure we got here for instruction we have a kprobe on */
459 if (((unsigned long)cur->ainsn.insn + len) != regs->nip)
460 return 0;
461
462 if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
463 kcb->kprobe_status = KPROBE_HIT_SSDONE;
464 cur->post_handler(cur, regs, 0);
465 }
466
467 /* Adjust nip to after the single-stepped instruction */
468 regs_set_return_ip(regs, (unsigned long)cur->addr + len);
469 regs_set_return_msr(regs, regs->msr | kcb->kprobe_saved_msr);
470
471 /*Restore back the original saved kprobes variables and continue. */
472 if (kcb->kprobe_status == KPROBE_REENTER) {
473 restore_previous_kprobe(kcb);
474 goto out;
475 }
476 reset_current_kprobe();
477 out:
478 preempt_enable();
479
480 /*
481 * if somebody else is singlestepping across a probe point, msr
482 * will have DE/SE set, in which case, continue the remaining processing
483 * of do_debug, as if this is not a probe hit.
484 */
485 if (regs->msr & MSR_SINGLESTEP)
486 return 0;
487
488 return 1;
489 }
490 NOKPROBE_SYMBOL(kprobe_post_handler);
491
492 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
493 {
494 struct kprobe *cur = kprobe_running();
495 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
496 const struct exception_table_entry *entry;
497
498 switch(kcb->kprobe_status) {
499 case KPROBE_HIT_SS:
500 case KPROBE_REENTER:
501 /*
502 * We are here because the instruction being single
503 * stepped caused a page fault. We reset the current
504 * kprobe and the nip points back to the probe address
505 * and allow the page fault handler to continue as a
506 * normal page fault.
507 */
508 regs_set_return_ip(regs, (unsigned long)cur->addr);
509 /* Turn off 'trace' bits */
510 regs_set_return_msr(regs,
511 (regs->msr & ~MSR_SINGLESTEP) |
512 kcb->kprobe_saved_msr);
513 if (kcb->kprobe_status == KPROBE_REENTER)
514 restore_previous_kprobe(kcb);
515 else
516 reset_current_kprobe();
517 preempt_enable();
518 break;
519 case KPROBE_HIT_ACTIVE:
520 case KPROBE_HIT_SSDONE:
521 /*
522 * In case the user-specified fault handler returned
523 * zero, try to fix up.
524 */
525 if ((entry = search_exception_tables(regs->nip)) != NULL) {
526 regs_set_return_ip(regs, extable_fixup(entry));
527 return 1;
528 }
529
530 /*
531 * fixup_exception() could not handle it,
532 * Let do_page_fault() fix it.
533 */
534 break;
535 default:
536 break;
537 }
538 return 0;
539 }
540 NOKPROBE_SYMBOL(kprobe_fault_handler);
541
542 static struct kprobe trampoline_p = {
543 .addr = (kprobe_opcode_t *) &__kretprobe_trampoline,
544 .pre_handler = trampoline_probe_handler
545 };
546
547 int __init arch_init_kprobes(void)
548 {
549 return register_kprobe(&trampoline_p);
550 }
551
552 int arch_trampoline_kprobe(struct kprobe *p)
553 {
554 if (p->addr == (kprobe_opcode_t *)&__kretprobe_trampoline)
555 return 1;
556
557 return 0;
558 }
559 NOKPROBE_SYMBOL(arch_trampoline_kprobe);
560
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