1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * Copyright (C) 2007 Alan Stern
4 * Copyright (C) IBM Corporation, 2009
5 * Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
6 *
7 * Thanks to Ingo Molnar for his many suggestions.
8 *
9 * Authors: Alan Stern <stern@rowland.harvard.edu>
10 * K.Prasad <prasad@linux.vnet.ibm.com>
11 * Frederic Weisbecker <fweisbec@gmail.com>
12 */
13
14 /*
15 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
16 * using the CPU's debug registers.
17 * This file contains the arch-independent routines.
18 */
19
20 #include <linux/irqflags.h>
21 #include <linux/kallsyms.h>
22 #include <linux/notifier.h>
23 #include <linux/kprobes.h>
24 #include <linux/kdebug.h>
25 #include <linux/kernel.h>
26 #include <linux/module.h>
27 #include <linux/percpu.h>
28 #include <linux/sched.h>
29 #include <linux/init.h>
30 #include <linux/slab.h>
31 #include <linux/list.h>
32 #include <linux/cpu.h>
33 #include <linux/smp.h>
34 #include <linux/bug.h>
35
36 #include <linux/hw_breakpoint.h>
37 /*
38 * Constraints data
39 */
40 struct bp_cpuinfo {
41 /* Number of pinned cpu breakpoints in a cpu */
42 unsigned int cpu_pinned;
43 /* tsk_pinned[n] is the number of tasks having n+1 breakpoints */
44 unsigned int *tsk_pinned;
45 /* Number of non-pinned cpu/task breakpoints in a cpu */
46 unsigned int flexible; /* XXX: placeholder, see fetch_this_slot() */
47 };
48
49 static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
50 static int nr_slots[TYPE_MAX];
51
52 static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
53 {
54 return per_cpu_ptr(bp_cpuinfo + type, cpu);
55 }
56
57 /* Keep track of the breakpoints attached to tasks */
58 static LIST_HEAD(bp_task_head);
59
60 static int constraints_initialized;
61
62 /* Gather the number of total pinned and un-pinned bp in a cpuset */
63 struct bp_busy_slots {
64 unsigned int pinned;
65 unsigned int flexible;
66 };
67
68 /* Serialize accesses to the above constraints */
69 static DEFINE_MUTEX(nr_bp_mutex);
70
71 __weak int hw_breakpoint_weight(struct perf_event *bp)
72 {
73 return 1;
74 }
75
76 static inline enum bp_type_idx find_slot_idx(u64 bp_type)
77 {
78 if (bp_type & HW_BREAKPOINT_RW)
79 return TYPE_DATA;
80
81 return TYPE_INST;
82 }
83
84 /*
85 * Report the maximum number of pinned breakpoints a task
86 * have in this cpu
87 */
88 static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
89 {
90 unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
91 int i;
92
93 for (i = nr_slots[type] - 1; i >= 0; i--) {
94 if (tsk_pinned[i] > 0)
95 return i + 1;
96 }
97
98 return 0;
99 }
100
101 /*
102 * Count the number of breakpoints of the same type and same task.
103 * The given event must be not on the list.
104 */
105 static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
106 {
107 struct task_struct *tsk = bp->hw.target;
108 struct perf_event *iter;
109 int count = 0;
110
111 list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
112 if (iter->hw.target == tsk &&
113 find_slot_idx(iter->attr.bp_type) == type &&
114 (iter->cpu < 0 || cpu == iter->cpu))
115 count += hw_breakpoint_weight(iter);
116 }
117
118 return count;
119 }
120
121 static const struct cpumask *cpumask_of_bp(struct perf_event *bp)
122 {
123 if (bp->cpu >= 0)
124 return cpumask_of(bp->cpu);
125 return cpu_possible_mask;
126 }
127
128 /*
129 * Report the number of pinned/un-pinned breakpoints we have in
130 * a given cpu (cpu > -1) or in all of them (cpu = -1).
131 */
132 static void
133 fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
134 enum bp_type_idx type)
135 {
136 const struct cpumask *cpumask = cpumask_of_bp(bp);
137 int cpu;
138
139 for_each_cpu(cpu, cpumask) {
140 struct bp_cpuinfo *info = get_bp_info(cpu, type);
141 int nr;
142
143 nr = info->cpu_pinned;
144 if (!bp->hw.target)
145 nr += max_task_bp_pinned(cpu, type);
146 else
147 nr += task_bp_pinned(cpu, bp, type);
148
149 if (nr > slots->pinned)
150 slots->pinned = nr;
151
152 nr = info->flexible;
153 if (nr > slots->flexible)
154 slots->flexible = nr;
155 }
156 }
157
158 /*
159 * For now, continue to consider flexible as pinned, until we can
160 * ensure no flexible event can ever be scheduled before a pinned event
161 * in a same cpu.
162 */
163 static void
164 fetch_this_slot(struct bp_busy_slots *slots, int weight)
165 {
166 slots->pinned += weight;
167 }
168
169 /*
170 * Add a pinned breakpoint for the given task in our constraint table
171 */
172 static void toggle_bp_task_slot(struct perf_event *bp, int cpu,
173 enum bp_type_idx type, int weight)
174 {
175 unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
176 int old_idx, new_idx;
177
178 old_idx = task_bp_pinned(cpu, bp, type) - 1;
179 new_idx = old_idx + weight;
180
181 if (old_idx >= 0)
182 tsk_pinned[old_idx]--;
183 if (new_idx >= 0)
184 tsk_pinned[new_idx]++;
185 }
186
187 /*
188 * Add/remove the given breakpoint in our constraint table
189 */
190 static void
191 toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
192 int weight)
193 {
194 const struct cpumask *cpumask = cpumask_of_bp(bp);
195 int cpu;
196
197 if (!enable)
198 weight = -weight;
199
200 /* Pinned counter cpu profiling */
201 if (!bp->hw.target) {
202 get_bp_info(bp->cpu, type)->cpu_pinned += weight;
203 return;
204 }
205
206 /* Pinned counter task profiling */
207 for_each_cpu(cpu, cpumask)
208 toggle_bp_task_slot(bp, cpu, type, weight);
209
210 if (enable)
211 list_add_tail(&bp->hw.bp_list, &bp_task_head);
212 else
213 list_del(&bp->hw.bp_list);
214 }
215
216 /*
217 * Function to perform processor-specific cleanup during unregistration
218 */
219 __weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
220 {
221 /*
222 * A weak stub function here for those archs that don't define
223 * it inside arch/.../kernel/hw_breakpoint.c
224 */
225 }
226
227 /*
228 * Constraints to check before allowing this new breakpoint counter:
229 *
230 * == Non-pinned counter == (Considered as pinned for now)
231 *
232 * - If attached to a single cpu, check:
233 *
234 * (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
235 * + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
236 *
237 * -> If there are already non-pinned counters in this cpu, it means
238 * there is already a free slot for them.
239 * Otherwise, we check that the maximum number of per task
240 * breakpoints (for this cpu) plus the number of per cpu breakpoint
241 * (for this cpu) doesn't cover every registers.
242 *
243 * - If attached to every cpus, check:
244 *
245 * (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
246 * + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
247 *
248 * -> This is roughly the same, except we check the number of per cpu
249 * bp for every cpu and we keep the max one. Same for the per tasks
250 * breakpoints.
251 *
252 *
253 * == Pinned counter ==
254 *
255 * - If attached to a single cpu, check:
256 *
257 * ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
258 * + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
259 *
260 * -> Same checks as before. But now the info->flexible, if any, must keep
261 * one register at least (or they will never be fed).
262 *
263 * - If attached to every cpus, check:
264 *
265 * ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
266 * + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
267 */
268 static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
269 {
270 struct bp_busy_slots slots = {0};
271 enum bp_type_idx type;
272 int weight;
273
274 /* We couldn't initialize breakpoint constraints on boot */
275 if (!constraints_initialized)
276 return -ENOMEM;
277
278 /* Basic checks */
279 if (bp_type == HW_BREAKPOINT_EMPTY ||
280 bp_type == HW_BREAKPOINT_INVALID)
281 return -EINVAL;
282
283 type = find_slot_idx(bp_type);
284 weight = hw_breakpoint_weight(bp);
285
286 fetch_bp_busy_slots(&slots, bp, type);
287 /*
288 * Simulate the addition of this breakpoint to the constraints
289 * and see the result.
290 */
291 fetch_this_slot(&slots, weight);
292
293 /* Flexible counters need to keep at least one slot */
294 if (slots.pinned + (!!slots.flexible) > nr_slots[type])
295 return -ENOSPC;
296
297 toggle_bp_slot(bp, true, type, weight);
298
299 return 0;
300 }
301
302 int reserve_bp_slot(struct perf_event *bp)
303 {
304 int ret;
305
306 mutex_lock(&nr_bp_mutex);
307
308 ret = __reserve_bp_slot(bp, bp->attr.bp_type);
309
310 mutex_unlock(&nr_bp_mutex);
311
312 return ret;
313 }
314
315 static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
316 {
317 enum bp_type_idx type;
318 int weight;
319
320 type = find_slot_idx(bp_type);
321 weight = hw_breakpoint_weight(bp);
322 toggle_bp_slot(bp, false, type, weight);
323 }
324
325 void release_bp_slot(struct perf_event *bp)
326 {
327 mutex_lock(&nr_bp_mutex);
328
329 arch_unregister_hw_breakpoint(bp);
330 __release_bp_slot(bp, bp->attr.bp_type);
331
332 mutex_unlock(&nr_bp_mutex);
333 }
334
335 static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
336 {
337 int err;
338
339 __release_bp_slot(bp, old_type);
340
341 err = __reserve_bp_slot(bp, new_type);
342 if (err) {
343 /*
344 * Reserve the old_type slot back in case
345 * there's no space for the new type.
346 *
347 * This must succeed, because we just released
348 * the old_type slot in the __release_bp_slot
349 * call above. If not, something is broken.
350 */
351 WARN_ON(__reserve_bp_slot(bp, old_type));
352 }
353
354 return err;
355 }
356
357 static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
358 {
359 int ret;
360
361 mutex_lock(&nr_bp_mutex);
362 ret = __modify_bp_slot(bp, old_type, new_type);
363 mutex_unlock(&nr_bp_mutex);
364 return ret;
365 }
366
367 /*
368 * Allow the kernel debugger to reserve breakpoint slots without
369 * taking a lock using the dbg_* variant of for the reserve and
370 * release breakpoint slots.
371 */
372 int dbg_reserve_bp_slot(struct perf_event *bp)
373 {
374 if (mutex_is_locked(&nr_bp_mutex))
375 return -1;
376
377 return __reserve_bp_slot(bp, bp->attr.bp_type);
378 }
379
380 int dbg_release_bp_slot(struct perf_event *bp)
381 {
382 if (mutex_is_locked(&nr_bp_mutex))
383 return -1;
384
385 __release_bp_slot(bp, bp->attr.bp_type);
386
387 return 0;
388 }
389
390 static int hw_breakpoint_parse(struct perf_event *bp,
391 const struct perf_event_attr *attr,
392 struct arch_hw_breakpoint *hw)
393 {
394 int err;
395
396 err = hw_breakpoint_arch_parse(bp, attr, hw);
397 if (err)
398 return err;
399
400 if (arch_check_bp_in_kernelspace(hw)) {
401 if (attr->exclude_kernel)
402 return -EINVAL;
403 /*
404 * Don't let unprivileged users set a breakpoint in the trap
405 * path to avoid trap recursion attacks.
406 */
407 if (!capable(CAP_SYS_ADMIN))
408 return -EPERM;
409 }
410
411 return 0;
412 }
413
414 int register_perf_hw_breakpoint(struct perf_event *bp)
415 {
416 struct arch_hw_breakpoint hw = { };
417 int err;
418
419 err = reserve_bp_slot(bp);
420 if (err)
421 return err;
422
423 err = hw_breakpoint_parse(bp, &bp->attr, &hw);
424 if (err) {
425 release_bp_slot(bp);
426 return err;
427 }
428
429 bp->hw.info = hw;
430
431 return 0;
432 }
433
434 /**
435 * register_user_hw_breakpoint - register a hardware breakpoint for user space
436 * @attr: breakpoint attributes
437 * @triggered: callback to trigger when we hit the breakpoint
438 * @tsk: pointer to 'task_struct' of the process to which the address belongs
439 */
440 struct perf_event *
441 register_user_hw_breakpoint(struct perf_event_attr *attr,
442 perf_overflow_handler_t triggered,
443 void *context,
444 struct task_struct *tsk)
445 {
446 return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
447 context);
448 }
449 EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
450
451 static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
452 struct perf_event_attr *from)
453 {
454 to->bp_addr = from->bp_addr;
455 to->bp_type = from->bp_type;
456 to->bp_len = from->bp_len;
457 to->disabled = from->disabled;
458 }
459
460 int
461 modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
462 bool check)
463 {
464 struct arch_hw_breakpoint hw = { };
465 int err;
466
467 err = hw_breakpoint_parse(bp, attr, &hw);
468 if (err)
469 return err;
470
471 if (check) {
472 struct perf_event_attr old_attr;
473
474 old_attr = bp->attr;
475 hw_breakpoint_copy_attr(&old_attr, attr);
476 if (memcmp(&old_attr, attr, sizeof(*attr)))
477 return -EINVAL;
478 }
479
480 if (bp->attr.bp_type != attr->bp_type) {
481 err = modify_bp_slot(bp, bp->attr.bp_type, attr->bp_type);
482 if (err)
483 return err;
484 }
485
486 hw_breakpoint_copy_attr(&bp->attr, attr);
487 bp->hw.info = hw;
488
489 return 0;
490 }
491
492 /**
493 * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
494 * @bp: the breakpoint structure to modify
495 * @attr: new breakpoint attributes
496 */
497 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
498 {
499 int err;
500
501 /*
502 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
503 * will not be possible to raise IPIs that invoke __perf_event_disable.
504 * So call the function directly after making sure we are targeting the
505 * current task.
506 */
507 if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
508 perf_event_disable_local(bp);
509 else
510 perf_event_disable(bp);
511
512 err = modify_user_hw_breakpoint_check(bp, attr, false);
513
514 if (!bp->attr.disabled)
515 perf_event_enable(bp);
516
517 return err;
518 }
519 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
520
521 /**
522 * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
523 * @bp: the breakpoint structure to unregister
524 */
525 void unregister_hw_breakpoint(struct perf_event *bp)
526 {
527 if (!bp)
528 return;
529 perf_event_release_kernel(bp);
530 }
531 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
532
533 /**
534 * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
535 * @attr: breakpoint attributes
536 * @triggered: callback to trigger when we hit the breakpoint
537 *
538 * @return a set of per_cpu pointers to perf events
539 */
540 struct perf_event * __percpu *
541 register_wide_hw_breakpoint(struct perf_event_attr *attr,
542 perf_overflow_handler_t triggered,
543 void *context)
544 {
545 struct perf_event * __percpu *cpu_events, *bp;
546 long err = 0;
547 int cpu;
548
549 cpu_events = alloc_percpu(typeof(*cpu_events));
550 if (!cpu_events)
551 return (void __percpu __force *)ERR_PTR(-ENOMEM);
552
553 get_online_cpus();
554 for_each_online_cpu(cpu) {
555 bp = perf_event_create_kernel_counter(attr, cpu, NULL,
556 triggered, context);
557 if (IS_ERR(bp)) {
558 err = PTR_ERR(bp);
559 break;
560 }
561
562 per_cpu(*cpu_events, cpu) = bp;
563 }
564 put_online_cpus();
565
566 if (likely(!err))
567 return cpu_events;
568
569 unregister_wide_hw_breakpoint(cpu_events);
570 return (void __percpu __force *)ERR_PTR(err);
571 }
572 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
573
574 /**
575 * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
576 * @cpu_events: the per cpu set of events to unregister
577 */
578 void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
579 {
580 int cpu;
581
582 for_each_possible_cpu(cpu)
583 unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
584
585 free_percpu(cpu_events);
586 }
587 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
588
589 static struct notifier_block hw_breakpoint_exceptions_nb = {
590 .notifier_call = hw_breakpoint_exceptions_notify,
591 /* we need to be notified first */
592 .priority = 0x7fffffff
593 };
594
595 static void bp_perf_event_destroy(struct perf_event *event)
596 {
597 release_bp_slot(event);
598 }
599
600 static int hw_breakpoint_event_init(struct perf_event *bp)
601 {
602 int err;
603
604 if (bp->attr.type != PERF_TYPE_BREAKPOINT)
605 return -ENOENT;
606
607 /*
608 * no branch sampling for breakpoint events
609 */
610 if (has_branch_stack(bp))
611 return -EOPNOTSUPP;
612
613 err = register_perf_hw_breakpoint(bp);
614 if (err)
615 return err;
616
617 bp->destroy = bp_perf_event_destroy;
618
619 return 0;
620 }
621
622 static int hw_breakpoint_add(struct perf_event *bp, int flags)
623 {
624 if (!(flags & PERF_EF_START))
625 bp->hw.state = PERF_HES_STOPPED;
626
627 if (is_sampling_event(bp)) {
628 bp->hw.last_period = bp->hw.sample_period;
629 perf_swevent_set_period(bp);
630 }
631
632 return arch_install_hw_breakpoint(bp);
633 }
634
635 static void hw_breakpoint_del(struct perf_event *bp, int flags)
636 {
637 arch_uninstall_hw_breakpoint(bp);
638 }
639
640 static void hw_breakpoint_start(struct perf_event *bp, int flags)
641 {
642 bp->hw.state = 0;
643 }
644
645 static void hw_breakpoint_stop(struct perf_event *bp, int flags)
646 {
647 bp->hw.state = PERF_HES_STOPPED;
648 }
649
650 static struct pmu perf_breakpoint = {
651 .task_ctx_nr = perf_sw_context, /* could eventually get its own */
652
653 .event_init = hw_breakpoint_event_init,
654 .add = hw_breakpoint_add,
655 .del = hw_breakpoint_del,
656 .start = hw_breakpoint_start,
657 .stop = hw_breakpoint_stop,
658 .read = hw_breakpoint_pmu_read,
659 };
660
661 int __init init_hw_breakpoint(void)
662 {
663 int cpu, err_cpu;
664 int i;
665
666 for (i = 0; i < TYPE_MAX; i++)
667 nr_slots[i] = hw_breakpoint_slots(i);
668
669 for_each_possible_cpu(cpu) {
670 for (i = 0; i < TYPE_MAX; i++) {
671 struct bp_cpuinfo *info = get_bp_info(cpu, i);
672
673 info->tsk_pinned = kcalloc(nr_slots[i], sizeof(int),
674 GFP_KERNEL);
675 if (!info->tsk_pinned)
676 goto err_alloc;
677 }
678 }
679
680 constraints_initialized = 1;
681
682 perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
683
684 return register_die_notifier(&hw_breakpoint_exceptions_nb);
685
686 err_alloc:
687 for_each_possible_cpu(err_cpu) {
688 for (i = 0; i < TYPE_MAX; i++)
689 kfree(get_bp_info(err_cpu, i)->tsk_pinned);
690 if (err_cpu == cpu)
691 break;
692 }
693
694 return -ENOMEM;
695 }
696
697
698
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.