1 // SPDX-License-Identifier: GPL-2.0
2 /* Support for MMIO probes.
3 * Benefit many code from kprobes
4 * (C) 2002 Louis Zhuang <louis.zhuang@intel.com>.
5 * 2007 Alexander Eichner
6 * 2008 Pekka Paalanen <pq@iki.fi>
7 */
8
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10
11 #include <linux/list.h>
12 #include <linux/rculist.h>
13 #include <linux/spinlock.h>
14 #include <linux/hash.h>
15 #include <linux/export.h>
16 #include <linux/kernel.h>
17 #include <linux/uaccess.h>
18 #include <linux/ptrace.h>
19 #include <linux/preempt.h>
20 #include <linux/percpu.h>
21 #include <linux/kdebug.h>
22 #include <linux/mutex.h>
23 #include <linux/io.h>
24 #include <linux/slab.h>
25 #include <asm/cacheflush.h>
26 #include <asm/tlbflush.h>
27 #include <linux/errno.h>
28 #include <asm/debugreg.h>
29 #include <linux/mmiotrace.h>
30
31 #define KMMIO_PAGE_HASH_BITS 4
32 #define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS)
33
34 struct kmmio_fault_page {
35 struct list_head list;
36 struct kmmio_fault_page *release_next;
37 unsigned long addr; /* the requested address */
38 pteval_t old_presence; /* page presence prior to arming */
39 bool armed;
40
41 /*
42 * Number of times this page has been registered as a part
43 * of a probe. If zero, page is disarmed and this may be freed.
44 * Used only by writers (RCU) and post_kmmio_handler().
45 * Protected by kmmio_lock, when linked into kmmio_page_table.
46 */
47 int count;
48
49 bool scheduled_for_release;
50 };
51
52 struct kmmio_delayed_release {
53 struct rcu_head rcu;
54 struct kmmio_fault_page *release_list;
55 };
56
57 struct kmmio_context {
58 struct kmmio_fault_page *fpage;
59 struct kmmio_probe *probe;
60 unsigned long saved_flags;
61 unsigned long addr;
62 int active;
63 };
64
65 /*
66 * The kmmio_lock is taken in int3 context, which is treated as NMI context.
67 * This causes lockdep to complain about it bein in both NMI and normal
68 * context. Hide it from lockdep, as it should not have any other locks
69 * taken under it, and this is only enabled for debugging mmio anyway.
70 */
71 static arch_spinlock_t kmmio_lock = __ARCH_SPIN_LOCK_UNLOCKED;
72
73 /* Protected by kmmio_lock */
74 unsigned int kmmio_count;
75
76 /* Read-protected by RCU, write-protected by kmmio_lock. */
77 static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
78 static LIST_HEAD(kmmio_probes);
79
80 static struct list_head *kmmio_page_list(unsigned long addr)
81 {
82 unsigned int l;
83 pte_t *pte = lookup_address(addr, &l);
84
85 if (!pte)
86 return NULL;
87 addr &= page_level_mask(l);
88
89 return &kmmio_page_table[hash_long(addr, KMMIO_PAGE_HASH_BITS)];
90 }
91
92 /* Accessed per-cpu */
93 static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx);
94
95 /*
96 * this is basically a dynamic stabbing problem:
97 * Could use the existing prio tree code or
98 * Possible better implementations:
99 * The Interval Skip List: A Data Structure for Finding All Intervals That
100 * Overlap a Point (might be simple)
101 * Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup
102 */
103 /* Get the kmmio at this addr (if any). You must be holding RCU read lock. */
104 static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
105 {
106 struct kmmio_probe *p;
107 list_for_each_entry_rcu(p, &kmmio_probes, list) {
108 if (addr >= p->addr && addr < (p->addr + p->len))
109 return p;
110 }
111 return NULL;
112 }
113
114 /* You must be holding RCU read lock. */
115 static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long addr)
116 {
117 struct list_head *head;
118 struct kmmio_fault_page *f;
119 unsigned int l;
120 pte_t *pte = lookup_address(addr, &l);
121
122 if (!pte)
123 return NULL;
124 addr &= page_level_mask(l);
125 head = kmmio_page_list(addr);
126 list_for_each_entry_rcu(f, head, list) {
127 if (f->addr == addr)
128 return f;
129 }
130 return NULL;
131 }
132
133 static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
134 {
135 pmd_t new_pmd;
136 pmdval_t v = pmd_val(*pmd);
137 if (clear) {
138 *old = v;
139 new_pmd = pmd_mkinvalid(*pmd);
140 } else {
141 /* Presume this has been called with clear==true previously */
142 new_pmd = __pmd(*old);
143 }
144 set_pmd(pmd, new_pmd);
145 }
146
147 static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
148 {
149 pteval_t v = pte_val(*pte);
150 if (clear) {
151 *old = v;
152 /* Nothing should care about address */
153 pte_clear(&init_mm, 0, pte);
154 } else {
155 /* Presume this has been called with clear==true previously */
156 set_pte_atomic(pte, __pte(*old));
157 }
158 }
159
160 static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
161 {
162 unsigned int level;
163 pte_t *pte = lookup_address(f->addr, &level);
164
165 if (!pte) {
166 pr_err("no pte for addr 0x%08lx\n", f->addr);
167 return -1;
168 }
169
170 switch (level) {
171 case PG_LEVEL_2M:
172 clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
173 break;
174 case PG_LEVEL_4K:
175 clear_pte_presence(pte, clear, &f->old_presence);
176 break;
177 default:
178 pr_err("unexpected page level 0x%x.\n", level);
179 return -1;
180 }
181
182 flush_tlb_one_kernel(f->addr);
183 return 0;
184 }
185
186 /*
187 * Mark the given page as not present. Access to it will trigger a fault.
188 *
189 * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
190 * protection is ignored here. RCU read lock is assumed held, so the struct
191 * will not disappear unexpectedly. Furthermore, the caller must guarantee,
192 * that double arming the same virtual address (page) cannot occur.
193 *
194 * Double disarming on the other hand is allowed, and may occur when a fault
195 * and mmiotrace shutdown happen simultaneously.
196 */
197 static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
198 {
199 int ret;
200 WARN_ONCE(f->armed, KERN_ERR pr_fmt("kmmio page already armed.\n"));
201 if (f->armed) {
202 pr_warn("double-arm: addr 0x%08lx, ref %d, old %d\n",
203 f->addr, f->count, !!f->old_presence);
204 }
205 ret = clear_page_presence(f, true);
206 WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming at 0x%08lx failed.\n"),
207 f->addr);
208 f->armed = true;
209 return ret;
210 }
211
212 /** Restore the given page to saved presence state. */
213 static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
214 {
215 int ret = clear_page_presence(f, false);
216 WARN_ONCE(ret < 0,
217 KERN_ERR "kmmio disarming at 0x%08lx failed.\n", f->addr);
218 f->armed = false;
219 }
220
221 /*
222 * This is being called from do_page_fault().
223 *
224 * We may be in an interrupt or a critical section. Also prefecthing may
225 * trigger a page fault. We may be in the middle of process switch.
226 * We cannot take any locks, because we could be executing especially
227 * within a kmmio critical section.
228 *
229 * Local interrupts are disabled, so preemption cannot happen.
230 * Do not enable interrupts, do not sleep, and watch out for other CPUs.
231 */
232 /*
233 * Interrupts are disabled on entry as trap3 is an interrupt gate
234 * and they remain disabled throughout this function.
235 */
236 int kmmio_handler(struct pt_regs *regs, unsigned long addr)
237 {
238 struct kmmio_context *ctx;
239 struct kmmio_fault_page *faultpage;
240 int ret = 0; /* default to fault not handled */
241 unsigned long page_base = addr;
242 unsigned int l;
243 pte_t *pte = lookup_address(addr, &l);
244 if (!pte)
245 return -EINVAL;
246 page_base &= page_level_mask(l);
247
248 /*
249 * Hold the RCU read lock over single stepping to avoid looking
250 * up the probe and kmmio_fault_page again. The rcu_read_lock_sched()
251 * also disables preemption and prevents process switch during
252 * the single stepping. We can only handle one active kmmio trace
253 * per cpu, so ensure that we finish it before something else
254 * gets to run.
255 */
256 rcu_read_lock_sched_notrace();
257
258 faultpage = get_kmmio_fault_page(page_base);
259 if (!faultpage) {
260 /*
261 * Either this page fault is not caused by kmmio, or
262 * another CPU just pulled the kmmio probe from under
263 * our feet. The latter case should not be possible.
264 */
265 goto no_kmmio;
266 }
267
268 ctx = this_cpu_ptr(&kmmio_ctx);
269 if (ctx->active) {
270 if (page_base == ctx->addr) {
271 /*
272 * A second fault on the same page means some other
273 * condition needs handling by do_page_fault(), the
274 * page really not being present is the most common.
275 */
276 pr_debug("secondary hit for 0x%08lx CPU %d.\n",
277 addr, smp_processor_id());
278
279 if (!faultpage->old_presence)
280 pr_info("unexpected secondary hit for address 0x%08lx on CPU %d.\n",
281 addr, smp_processor_id());
282 } else {
283 /*
284 * Prevent overwriting already in-flight context.
285 * This should not happen, let's hope disarming at
286 * least prevents a panic.
287 */
288 pr_emerg("recursive probe hit on CPU %d, for address 0x%08lx. Ignoring.\n",
289 smp_processor_id(), addr);
290 pr_emerg("previous hit was at 0x%08lx.\n", ctx->addr);
291 disarm_kmmio_fault_page(faultpage);
292 }
293 goto no_kmmio;
294 }
295 ctx->active++;
296
297 ctx->fpage = faultpage;
298 ctx->probe = get_kmmio_probe(page_base);
299 ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
300 ctx->addr = page_base;
301
302 if (ctx->probe && ctx->probe->pre_handler)
303 ctx->probe->pre_handler(ctx->probe, regs, addr);
304
305 /*
306 * Enable single-stepping and disable interrupts for the faulting
307 * context. Local interrupts must not get enabled during stepping.
308 */
309 regs->flags |= X86_EFLAGS_TF;
310 regs->flags &= ~X86_EFLAGS_IF;
311
312 /* Now we set present bit in PTE and single step. */
313 disarm_kmmio_fault_page(ctx->fpage);
314
315 /*
316 * If another cpu accesses the same page while we are stepping,
317 * the access will not be caught. It will simply succeed and the
318 * only downside is we lose the event. If this becomes a problem,
319 * the user should drop to single cpu before tracing.
320 */
321
322 return 1; /* fault handled */
323
324 no_kmmio:
325 rcu_read_unlock_sched_notrace();
326 return ret;
327 }
328
329 /*
330 * Interrupts are disabled on entry as trap1 is an interrupt gate
331 * and they remain disabled throughout this function.
332 * This must always get called as the pair to kmmio_handler().
333 */
334 static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
335 {
336 int ret = 0;
337 struct kmmio_context *ctx = this_cpu_ptr(&kmmio_ctx);
338
339 if (!ctx->active) {
340 /*
341 * debug traps without an active context are due to either
342 * something external causing them (f.e. using a debugger while
343 * mmio tracing enabled), or erroneous behaviour
344 */
345 pr_warn("unexpected debug trap on CPU %d.\n", smp_processor_id());
346 goto out;
347 }
348
349 if (ctx->probe && ctx->probe->post_handler)
350 ctx->probe->post_handler(ctx->probe, condition, regs);
351
352 /* Prevent racing against release_kmmio_fault_page(). */
353 arch_spin_lock(&kmmio_lock);
354 if (ctx->fpage->count)
355 arm_kmmio_fault_page(ctx->fpage);
356 arch_spin_unlock(&kmmio_lock);
357
358 regs->flags &= ~X86_EFLAGS_TF;
359 regs->flags |= ctx->saved_flags;
360
361 /* These were acquired in kmmio_handler(). */
362 ctx->active--;
363 BUG_ON(ctx->active);
364 rcu_read_unlock_sched_notrace();
365
366 /*
367 * if somebody else is singlestepping across a probe point, flags
368 * will have TF set, in which case, continue the remaining processing
369 * of do_debug, as if this is not a probe hit.
370 */
371 if (!(regs->flags & X86_EFLAGS_TF))
372 ret = 1;
373 out:
374 return ret;
375 }
376
377 /* You must be holding kmmio_lock. */
378 static int add_kmmio_fault_page(unsigned long addr)
379 {
380 struct kmmio_fault_page *f;
381
382 f = get_kmmio_fault_page(addr);
383 if (f) {
384 if (!f->count)
385 arm_kmmio_fault_page(f);
386 f->count++;
387 return 0;
388 }
389
390 f = kzalloc(sizeof(*f), GFP_ATOMIC);
391 if (!f)
392 return -1;
393
394 f->count = 1;
395 f->addr = addr;
396
397 if (arm_kmmio_fault_page(f)) {
398 kfree(f);
399 return -1;
400 }
401
402 list_add_rcu(&f->list, kmmio_page_list(f->addr));
403
404 return 0;
405 }
406
407 /* You must be holding kmmio_lock. */
408 static void release_kmmio_fault_page(unsigned long addr,
409 struct kmmio_fault_page **release_list)
410 {
411 struct kmmio_fault_page *f;
412
413 f = get_kmmio_fault_page(addr);
414 if (!f)
415 return;
416
417 f->count--;
418 BUG_ON(f->count < 0);
419 if (!f->count) {
420 disarm_kmmio_fault_page(f);
421 if (!f->scheduled_for_release) {
422 f->release_next = *release_list;
423 *release_list = f;
424 f->scheduled_for_release = true;
425 }
426 }
427 }
428
429 /*
430 * With page-unaligned ioremaps, one or two armed pages may contain
431 * addresses from outside the intended mapping. Events for these addresses
432 * are currently silently dropped. The events may result only from programming
433 * mistakes by accessing addresses before the beginning or past the end of a
434 * mapping.
435 */
436 int register_kmmio_probe(struct kmmio_probe *p)
437 {
438 unsigned long flags;
439 int ret = 0;
440 unsigned long size = 0;
441 unsigned long addr = p->addr & PAGE_MASK;
442 const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
443 unsigned int l;
444 pte_t *pte;
445
446 local_irq_save(flags);
447 arch_spin_lock(&kmmio_lock);
448 if (get_kmmio_probe(addr)) {
449 ret = -EEXIST;
450 goto out;
451 }
452
453 pte = lookup_address(addr, &l);
454 if (!pte) {
455 ret = -EINVAL;
456 goto out;
457 }
458
459 kmmio_count++;
460 list_add_rcu(&p->list, &kmmio_probes);
461 while (size < size_lim) {
462 if (add_kmmio_fault_page(addr + size))
463 pr_err("Unable to set page fault.\n");
464 size += page_level_size(l);
465 }
466 out:
467 arch_spin_unlock(&kmmio_lock);
468 local_irq_restore(flags);
469
470 /*
471 * XXX: What should I do here?
472 * Here was a call to global_flush_tlb(), but it does not exist
473 * anymore. It seems it's not needed after all.
474 */
475 return ret;
476 }
477 EXPORT_SYMBOL(register_kmmio_probe);
478
479 static void rcu_free_kmmio_fault_pages(struct rcu_head *head)
480 {
481 struct kmmio_delayed_release *dr = container_of(
482 head,
483 struct kmmio_delayed_release,
484 rcu);
485 struct kmmio_fault_page *f = dr->release_list;
486 while (f) {
487 struct kmmio_fault_page *next = f->release_next;
488 BUG_ON(f->count);
489 kfree(f);
490 f = next;
491 }
492 kfree(dr);
493 }
494
495 static void remove_kmmio_fault_pages(struct rcu_head *head)
496 {
497 struct kmmio_delayed_release *dr =
498 container_of(head, struct kmmio_delayed_release, rcu);
499 struct kmmio_fault_page *f = dr->release_list;
500 struct kmmio_fault_page **prevp = &dr->release_list;
501 unsigned long flags;
502
503 local_irq_save(flags);
504 arch_spin_lock(&kmmio_lock);
505 while (f) {
506 if (!f->count) {
507 list_del_rcu(&f->list);
508 prevp = &f->release_next;
509 } else {
510 *prevp = f->release_next;
511 f->release_next = NULL;
512 f->scheduled_for_release = false;
513 }
514 f = *prevp;
515 }
516 arch_spin_unlock(&kmmio_lock);
517 local_irq_restore(flags);
518
519 /* This is the real RCU destroy call. */
520 call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages);
521 }
522
523 /*
524 * Remove a kmmio probe. You have to synchronize_rcu() before you can be
525 * sure that the callbacks will not be called anymore. Only after that
526 * you may actually release your struct kmmio_probe.
527 *
528 * Unregistering a kmmio fault page has three steps:
529 * 1. release_kmmio_fault_page()
530 * Disarm the page, wait a grace period to let all faults finish.
531 * 2. remove_kmmio_fault_pages()
532 * Remove the pages from kmmio_page_table.
533 * 3. rcu_free_kmmio_fault_pages()
534 * Actually free the kmmio_fault_page structs as with RCU.
535 */
536 void unregister_kmmio_probe(struct kmmio_probe *p)
537 {
538 unsigned long flags;
539 unsigned long size = 0;
540 unsigned long addr = p->addr & PAGE_MASK;
541 const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
542 struct kmmio_fault_page *release_list = NULL;
543 struct kmmio_delayed_release *drelease;
544 unsigned int l;
545 pte_t *pte;
546
547 pte = lookup_address(addr, &l);
548 if (!pte)
549 return;
550
551 local_irq_save(flags);
552 arch_spin_lock(&kmmio_lock);
553 while (size < size_lim) {
554 release_kmmio_fault_page(addr + size, &release_list);
555 size += page_level_size(l);
556 }
557 list_del_rcu(&p->list);
558 kmmio_count--;
559 arch_spin_unlock(&kmmio_lock);
560 local_irq_restore(flags);
561
562 if (!release_list)
563 return;
564
565 drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
566 if (!drelease) {
567 pr_crit("leaking kmmio_fault_page objects.\n");
568 return;
569 }
570 drelease->release_list = release_list;
571
572 /*
573 * This is not really RCU here. We have just disarmed a set of
574 * pages so that they cannot trigger page faults anymore. However,
575 * we cannot remove the pages from kmmio_page_table,
576 * because a probe hit might be in flight on another CPU. The
577 * pages are collected into a list, and they will be removed from
578 * kmmio_page_table when it is certain that no probe hit related to
579 * these pages can be in flight. RCU grace period sounds like a
580 * good choice.
581 *
582 * If we removed the pages too early, kmmio page fault handler might
583 * not find the respective kmmio_fault_page and determine it's not
584 * a kmmio fault, when it actually is. This would lead to madness.
585 */
586 call_rcu(&drelease->rcu, remove_kmmio_fault_pages);
587 }
588 EXPORT_SYMBOL(unregister_kmmio_probe);
589
590 static int
591 kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args)
592 {
593 struct die_args *arg = args;
594 unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err);
595
596 if (val == DIE_DEBUG && (*dr6_p & DR_STEP))
597 if (post_kmmio_handler(*dr6_p, arg->regs) == 1) {
598 /*
599 * Reset the BS bit in dr6 (pointed by args->err) to
600 * denote completion of processing
601 */
602 *dr6_p &= ~DR_STEP;
603 return NOTIFY_STOP;
604 }
605
606 return NOTIFY_DONE;
607 }
608
609 static struct notifier_block nb_die = {
610 .notifier_call = kmmio_die_notifier
611 };
612
613 int kmmio_init(void)
614 {
615 int i;
616
617 for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++)
618 INIT_LIST_HEAD(&kmmio_page_table[i]);
619
620 return register_die_notifier(&nb_die);
621 }
622
623 void kmmio_cleanup(void)
624 {
625 int i;
626
627 unregister_die_notifier(&nb_die);
628 for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) {
629 WARN_ONCE(!list_empty(&kmmio_page_table[i]),
630 KERN_ERR "kmmio_page_table not empty at cleanup, any further tracing will leak memory.\n");
631 }
632 }
633
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