arch/x86/mm/kmmio.c

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