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