arch/x86/kernel/unwind_orc.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/objtool.h>
   3 #include <linux/module.h>
   4 #include <linux/sort.h>
   5 #include <asm/ptrace.h>
   6 #include <asm/stacktrace.h>
   7 #include <asm/unwind.h>
   8 #include <asm/orc_types.h>
   9 #include <asm/orc_lookup.h>
  10 #include <asm/orc_header.h>
  11
  12 ORC_HEADER;
  13
  14 #define orc_warn(fmt, ...) \
  15         printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)
  16
  17 #define orc_warn_current(args...)                                       \
  18 ({                                                                      \
  19         static bool dumped_before;                                      \
  20         if (state->task == current && !state->error) {                  \
  21                 orc_warn(args);                                         \
  22                 if (unwind_debug && !dumped_before) {                   \
  23                         dumped_before = true;                           \
  24                         unwind_dump(state);                             \
  25                 }                                                       \
  26         }                                                               \
  27 })
  28
  29 extern int __start_orc_unwind_ip[];
  30 extern int __stop_orc_unwind_ip[];
  31 extern struct orc_entry __start_orc_unwind[];
  32 extern struct orc_entry __stop_orc_unwind[];
  33
  34 static bool orc_init __ro_after_init;
  35 static bool unwind_debug __ro_after_init;
  36 static unsigned int lookup_num_blocks __ro_after_init;
  37
  38 static int __init unwind_debug_cmdline(char *str)
  39 {
  40         unwind_debug = true;
  41
  42         return 0;
  43 }
  44 early_param("unwind_debug", unwind_debug_cmdline);
  45
  46 static void unwind_dump(struct unwind_state *state)
  47 {
  48         static bool dumped_before;
  49         unsigned long word, *sp;
  50         struct stack_info stack_info = {0};
  51         unsigned long visit_mask = 0;
  52
  53         if (dumped_before)
  54                 return;
  55
  56         dumped_before = true;
  57
  58         printk_deferred("unwind stack type:%d next_sp:%p mask:0x%lx graph_idx:%d\n",
  59                         state->stack_info.type, state->stack_info.next_sp,
  60                         state->stack_mask, state->graph_idx);
  61
  62         for (sp = __builtin_frame_address(0); sp;
  63              sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
  64                 if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
  65                         break;
  66
  67                 for (; sp < stack_info.end; sp++) {
  68
  69                         word = READ_ONCE_NOCHECK(*sp);
  70
  71                         printk_deferred("%0*lx: %0*lx (%pB)\n", BITS_PER_LONG/4,
  72                                         (unsigned long)sp, BITS_PER_LONG/4,
  73                                         word, (void *)word);
  74                 }
  75         }
  76 }
  77
  78 static inline unsigned long orc_ip(const int *ip)
  79 {
  80         return (unsigned long)ip + *ip;
  81 }
  82
  83 static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
  84                                     unsigned int num_entries, unsigned long ip)
  85 {
  86         int *first = ip_table;
  87         int *last = ip_table + num_entries - 1;
  88         int *mid, *found = first;
  89
  90         if (!num_entries)
  91                 return NULL;
  92
  93         /*
  94          * Do a binary range search to find the rightmost duplicate of a given
  95          * starting address.  Some entries are section terminators which are
  96          * "weak" entries for ensuring there are no gaps.  They should be
  97          * ignored when they conflict with a real entry.
  98          */
  99         while (first <= last) {
 100                 mid = first + ((last - first) / 2);
 101
 102                 if (orc_ip(mid) <= ip) {
 103                         found = mid;
 104                         first = mid + 1;
 105                 } else
 106                         last = mid - 1;
 107         }
 108
 109         return u_table + (found - ip_table);
 110 }
 111
 112 #ifdef CONFIG_MODULES
 113 static struct orc_entry *orc_module_find(unsigned long ip)
 114 {
 115         struct module *mod;
 116
 117         mod = __module_address(ip);
 118         if (!mod || !mod->arch.orc_unwind || !mod->arch.orc_unwind_ip)
 119                 return NULL;
 120         return __orc_find(mod->arch.orc_unwind_ip, mod->arch.orc_unwind,
 121                           mod->arch.num_orcs, ip);
 122 }
 123 #else
 124 static struct orc_entry *orc_module_find(unsigned long ip)
 125 {
 126         return NULL;
 127 }
 128 #endif
 129
 130 #ifdef CONFIG_DYNAMIC_FTRACE
 131 static struct orc_entry *orc_find(unsigned long ip);
 132
 133 /*
 134  * Ftrace dynamic trampolines do not have orc entries of their own.
 135  * But they are copies of the ftrace entries that are static and
 136  * defined in ftrace_*.S, which do have orc entries.
 137  *
 138  * If the unwinder comes across a ftrace trampoline, then find the
 139  * ftrace function that was used to create it, and use that ftrace
 140  * function's orc entry, as the placement of the return code in
 141  * the stack will be identical.
 142  */
 143 static struct orc_entry *orc_ftrace_find(unsigned long ip)
 144 {
 145         struct ftrace_ops *ops;
 146         unsigned long tramp_addr, offset;
 147
 148         ops = ftrace_ops_trampoline(ip);
 149         if (!ops)
 150                 return NULL;
 151
 152         /* Set tramp_addr to the start of the code copied by the trampoline */
 153         if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
 154                 tramp_addr = (unsigned long)ftrace_regs_caller;
 155         else
 156                 tramp_addr = (unsigned long)ftrace_caller;
 157
 158         /* Now place tramp_addr to the location within the trampoline ip is at */
 159         offset = ip - ops->trampoline;
 160         tramp_addr += offset;
 161
 162         /* Prevent unlikely recursion */
 163         if (ip == tramp_addr)
 164                 return NULL;
 165
 166         return orc_find(tramp_addr);
 167 }
 168 #else
 169 static struct orc_entry *orc_ftrace_find(unsigned long ip)
 170 {
 171         return NULL;
 172 }
 173 #endif
 174
 175 /*
 176  * If we crash with IP==0, the last successfully executed instruction
 177  * was probably an indirect function call with a NULL function pointer,
 178  * and we don't have unwind information for NULL.
 179  * This hardcoded ORC entry for IP==0 allows us to unwind from a NULL function
 180  * pointer into its parent and then continue normally from there.
 181  */
 182 static struct orc_entry null_orc_entry = {
 183         .sp_offset = sizeof(long),
 184         .sp_reg = ORC_REG_SP,
 185         .bp_reg = ORC_REG_UNDEFINED,
 186         .type = ORC_TYPE_CALL
 187 };
 188
 189 /* Fake frame pointer entry -- used as a fallback for generated code */
 190 static struct orc_entry orc_fp_entry = {
 191         .type           = ORC_TYPE_CALL,
 192         .sp_reg         = ORC_REG_BP,
 193         .sp_offset      = 16,
 194         .bp_reg         = ORC_REG_PREV_SP,
 195         .bp_offset      = -16,
 196 };
 197
 198 static struct orc_entry *orc_find(unsigned long ip)
 199 {
 200         static struct orc_entry *orc;
 201
 202         if (ip == 0)
 203                 return &null_orc_entry;
 204
 205         /* For non-init vmlinux addresses, use the fast lookup table: */
 206         if (ip >= LOOKUP_START_IP && ip < LOOKUP_STOP_IP) {
 207                 unsigned int idx, start, stop;
 208
 209                 idx = (ip - LOOKUP_START_IP) / LOOKUP_BLOCK_SIZE;
 210
 211                 if (unlikely((idx >= lookup_num_blocks-1))) {
 212                         orc_warn("WARNING: bad lookup idx: idx=%u num=%u ip=%pB\n",
 213                                  idx, lookup_num_blocks, (void *)ip);
 214                         return NULL;
 215                 }
 216
 217                 start = orc_lookup[idx];
 218                 stop = orc_lookup[idx + 1] + 1;
 219
 220                 if (unlikely((__start_orc_unwind + start >= __stop_orc_unwind) ||
 221                              (__start_orc_unwind + stop > __stop_orc_unwind))) {
 222                         orc_warn("WARNING: bad lookup value: idx=%u num=%u start=%u stop=%u ip=%pB\n",
 223                                  idx, lookup_num_blocks, start, stop, (void *)ip);
 224                         return NULL;
 225                 }
 226
 227                 return __orc_find(__start_orc_unwind_ip + start,
 228                                   __start_orc_unwind + start, stop - start, ip);
 229         }
 230
 231         /* vmlinux .init slow lookup: */
 232         if (is_kernel_inittext(ip))
 233                 return __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
 234                                   __stop_orc_unwind_ip - __start_orc_unwind_ip, ip);
 235
 236         /* Module lookup: */
 237         orc = orc_module_find(ip);
 238         if (orc)
 239                 return orc;
 240
 241         return orc_ftrace_find(ip);
 242 }
 243
 244 #ifdef CONFIG_MODULES
 245
 246 static DEFINE_MUTEX(sort_mutex);
 247 static int *cur_orc_ip_table = __start_orc_unwind_ip;
 248 static struct orc_entry *cur_orc_table = __start_orc_unwind;
 249
 250 static void orc_sort_swap(void *_a, void *_b, int size)
 251 {
 252         struct orc_entry *orc_a, *orc_b;
 253         int *a = _a, *b = _b, tmp;
 254         int delta = _b - _a;
 255
 256         /* Swap the .orc_unwind_ip entries: */
 257         tmp = *a;
 258         *a = *b + delta;
 259         *b = tmp - delta;
 260
 261         /* Swap the corresponding .orc_unwind entries: */
 262         orc_a = cur_orc_table + (a - cur_orc_ip_table);
 263         orc_b = cur_orc_table + (b - cur_orc_ip_table);
 264         swap(*orc_a, *orc_b);
 265 }
 266
 267 static int orc_sort_cmp(const void *_a, const void *_b)
 268 {
 269         struct orc_entry *orc_a;
 270         const int *a = _a, *b = _b;
 271         unsigned long a_val = orc_ip(a);
 272         unsigned long b_val = orc_ip(b);
 273
 274         if (a_val > b_val)
 275                 return 1;
 276         if (a_val < b_val)
 277                 return -1;
 278
 279         /*
 280          * The "weak" section terminator entries need to always be first
 281          * to ensure the lookup code skips them in favor of real entries.
 282          * These terminator entries exist to handle any gaps created by
 283          * whitelisted .o files which didn't get objtool generation.
 284          */
 285         orc_a = cur_orc_table + (a - cur_orc_ip_table);
 286         return orc_a->type == ORC_TYPE_UNDEFINED ? -1 : 1;
 287 }
 288
 289 void unwind_module_init(struct module *mod, void *_orc_ip, size_t orc_ip_size,
 290                         void *_orc, size_t orc_size)
 291 {
 292         int *orc_ip = _orc_ip;
 293         struct orc_entry *orc = _orc;
 294         unsigned int num_entries = orc_ip_size / sizeof(int);
 295
 296         WARN_ON_ONCE(orc_ip_size % sizeof(int) != 0 ||
 297                      orc_size % sizeof(*orc) != 0 ||
 298                      num_entries != orc_size / sizeof(*orc));
 299
 300         /*
 301          * The 'cur_orc_*' globals allow the orc_sort_swap() callback to
 302          * associate an .orc_unwind_ip table entry with its corresponding
 303          * .orc_unwind entry so they can both be swapped.
 304          */
 305         mutex_lock(&sort_mutex);
 306         cur_orc_ip_table = orc_ip;
 307         cur_orc_table = orc;
 308         sort(orc_ip, num_entries, sizeof(int), orc_sort_cmp, orc_sort_swap);
 309         mutex_unlock(&sort_mutex);
 310
 311         mod->arch.orc_unwind_ip = orc_ip;
 312         mod->arch.orc_unwind = orc;
 313         mod->arch.num_orcs = num_entries;
 314 }
 315 #endif
 316
 317 void __init unwind_init(void)
 318 {
 319         size_t orc_ip_size = (void *)__stop_orc_unwind_ip - (void *)__start_orc_unwind_ip;
 320         size_t orc_size = (void *)__stop_orc_unwind - (void *)__start_orc_unwind;
 321         size_t num_entries = orc_ip_size / sizeof(int);
 322         struct orc_entry *orc;
 323         int i;
 324
 325         if (!num_entries || orc_ip_size % sizeof(int) != 0 ||
 326             orc_size % sizeof(struct orc_entry) != 0 ||
 327             num_entries != orc_size / sizeof(struct orc_entry)) {
 328                 orc_warn("WARNING: Bad or missing .orc_unwind table.  Disabling unwinder.\n");
 329                 return;
 330         }
 331
 332         /*
 333          * Note, the orc_unwind and orc_unwind_ip tables were already
 334          * sorted at build time via the 'sorttable' tool.
 335          * It's ready for binary search straight away, no need to sort it.
 336          */
 337
 338         /* Initialize the fast lookup table: */
 339         lookup_num_blocks = orc_lookup_end - orc_lookup;
 340         for (i = 0; i < lookup_num_blocks-1; i++) {
 341                 orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
 342                                  num_entries,
 343                                  LOOKUP_START_IP + (LOOKUP_BLOCK_SIZE * i));
 344                 if (!orc) {
 345                         orc_warn("WARNING: Corrupt .orc_unwind table.  Disabling unwinder.\n");
 346                         return;
 347                 }
 348
 349                 orc_lookup[i] = orc - __start_orc_unwind;
 350         }
 351
 352         /* Initialize the ending block: */
 353         orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind, num_entries,
 354                          LOOKUP_STOP_IP);
 355         if (!orc) {
 356                 orc_warn("WARNING: Corrupt .orc_unwind table.  Disabling unwinder.\n");
 357                 return;
 358         }
 359         orc_lookup[lookup_num_blocks-1] = orc - __start_orc_unwind;
 360
 361         orc_init = true;
 362 }
 363
 364 unsigned long unwind_get_return_address(struct unwind_state *state)
 365 {
 366         if (unwind_done(state))
 367                 return 0;
 368
 369         return __kernel_text_address(state->ip) ? state->ip : 0;
 370 }
 371 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 372
 373 unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
 374 {
 375         if (unwind_done(state))
 376                 return NULL;
 377
 378         if (state->regs)
 379                 return &state->regs->ip;
 380
 381         if (state->sp)
 382                 return (unsigned long *)state->sp - 1;
 383
 384         return NULL;
 385 }
 386
 387 static bool stack_access_ok(struct unwind_state *state, unsigned long _addr,
 388                             size_t len)
 389 {
 390         struct stack_info *info = &state->stack_info;
 391         void *addr = (void *)_addr;
 392
 393         if (on_stack(info, addr, len))
 394                 return true;
 395
 396         return !get_stack_info(addr, state->task, info, &state->stack_mask) &&
 397                 on_stack(info, addr, len);
 398 }
 399
 400 static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
 401                             unsigned long *val)
 402 {
 403         if (!stack_access_ok(state, addr, sizeof(long)))
 404                 return false;
 405
 406         *val = READ_ONCE_NOCHECK(*(unsigned long *)addr);
 407         return true;
 408 }
 409
 410 static bool deref_stack_regs(struct unwind_state *state, unsigned long addr,
 411                              unsigned long *ip, unsigned long *sp)
 412 {
 413         struct pt_regs *regs = (struct pt_regs *)addr;
 414
 415         /* x86-32 support will be more complicated due to the &regs->sp hack */
 416         BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_32));
 417
 418         if (!stack_access_ok(state, addr, sizeof(struct pt_regs)))
 419                 return false;
 420
 421         *ip = READ_ONCE_NOCHECK(regs->ip);
 422         *sp = READ_ONCE_NOCHECK(regs->sp);
 423         return true;
 424 }
 425
 426 static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr,
 427                                   unsigned long *ip, unsigned long *sp)
 428 {
 429         struct pt_regs *regs = (void *)addr - IRET_FRAME_OFFSET;
 430
 431         if (!stack_access_ok(state, addr, IRET_FRAME_SIZE))
 432                 return false;
 433
 434         *ip = READ_ONCE_NOCHECK(regs->ip);
 435         *sp = READ_ONCE_NOCHECK(regs->sp);
 436         return true;
 437 }
 438
 439 /*
 440  * If state->regs is non-NULL, and points to a full pt_regs, just get the reg
 441  * value from state->regs.
 442  *
 443  * Otherwise, if state->regs just points to IRET regs, and the previous frame
 444  * had full regs, it's safe to get the value from the previous regs.  This can
 445  * happen when early/late IRQ entry code gets interrupted by an NMI.
 446  */
 447 static bool get_reg(struct unwind_state *state, unsigned int reg_off,
 448                     unsigned long *val)
 449 {
 450         unsigned int reg = reg_off/8;
 451
 452         if (!state->regs)
 453                 return false;
 454
 455         if (state->full_regs) {
 456                 *val = READ_ONCE_NOCHECK(((unsigned long *)state->regs)[reg]);
 457                 return true;
 458         }
 459
 460         if (state->prev_regs) {
 461                 *val = READ_ONCE_NOCHECK(((unsigned long *)state->prev_regs)[reg]);
 462                 return true;
 463         }
 464
 465         return false;
 466 }
 467
 468 bool unwind_next_frame(struct unwind_state *state)
 469 {
 470         unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
 471         enum stack_type prev_type = state->stack_info.type;
 472         struct orc_entry *orc;
 473         bool indirect = false;
 474
 475         if (unwind_done(state))
 476                 return false;
 477
 478         /* Don't let modules unload while we're reading their ORC data. */
 479         preempt_disable();
 480
 481         /* End-of-stack check for user tasks: */
 482         if (state->regs && user_mode(state->regs))
 483                 goto the_end;
 484
 485         /*
 486          * Find the orc_entry associated with the text address.
 487          *
 488          * For a call frame (as opposed to a signal frame), state->ip points to
 489          * the instruction after the call.  That instruction's stack layout
 490          * could be different from the call instruction's layout, for example
 491          * if the call was to a noreturn function.  So get the ORC data for the
 492          * call instruction itself.
 493          */
 494         orc = orc_find(state->signal ? state->ip : state->ip - 1);
 495         if (!orc) {
 496                 /*
 497                  * As a fallback, try to assume this code uses a frame pointer.
 498                  * This is useful for generated code, like BPF, which ORC
 499                  * doesn't know about.  This is just a guess, so the rest of
 500                  * the unwind is no longer considered reliable.
 501                  */
 502                 orc = &orc_fp_entry;
 503                 state->error = true;
 504         } else {
 505                 if (orc->type == ORC_TYPE_UNDEFINED)
 506                         goto err;
 507
 508                 if (orc->type == ORC_TYPE_END_OF_STACK)
 509                         goto the_end;
 510         }
 511
 512         state->signal = orc->signal;
 513
 514         /* Find the previous frame's stack: */
 515         switch (orc->sp_reg) {
 516         case ORC_REG_SP:
 517                 sp = state->sp + orc->sp_offset;
 518                 break;
 519
 520         case ORC_REG_BP:
 521                 sp = state->bp + orc->sp_offset;
 522                 break;
 523
 524         case ORC_REG_SP_INDIRECT:
 525                 sp = state->sp;
 526                 indirect = true;
 527                 break;
 528
 529         case ORC_REG_BP_INDIRECT:
 530                 sp = state->bp + orc->sp_offset;
 531                 indirect = true;
 532                 break;
 533
 534         case ORC_REG_R10:
 535                 if (!get_reg(state, offsetof(struct pt_regs, r10), &sp)) {
 536                         orc_warn_current("missing R10 value at %pB\n",
 537                                          (void *)state->ip);
 538                         goto err;
 539                 }
 540                 break;
 541
 542         case ORC_REG_R13:
 543                 if (!get_reg(state, offsetof(struct pt_regs, r13), &sp)) {
 544                         orc_warn_current("missing R13 value at %pB\n",
 545                                          (void *)state->ip);
 546                         goto err;
 547                 }
 548                 break;
 549
 550         case ORC_REG_DI:
 551                 if (!get_reg(state, offsetof(struct pt_regs, di), &sp)) {
 552                         orc_warn_current("missing RDI value at %pB\n",
 553                                          (void *)state->ip);
 554                         goto err;
 555                 }
 556                 break;
 557
 558         case ORC_REG_DX:
 559                 if (!get_reg(state, offsetof(struct pt_regs, dx), &sp)) {
 560                         orc_warn_current("missing DX value at %pB\n",
 561                                          (void *)state->ip);
 562                         goto err;
 563                 }
 564                 break;
 565
 566         default:
 567                 orc_warn("unknown SP base reg %d at %pB\n",
 568                          orc->sp_reg, (void *)state->ip);
 569                 goto err;
 570         }
 571
 572         if (indirect) {
 573                 if (!deref_stack_reg(state, sp, &sp))
 574                         goto err;
 575
 576                 if (orc->sp_reg == ORC_REG_SP_INDIRECT)
 577                         sp += orc->sp_offset;
 578         }
 579
 580         /* Find IP, SP and possibly regs: */
 581         switch (orc->type) {
 582         case ORC_TYPE_CALL:
 583                 ip_p = sp - sizeof(long);
 584
 585                 if (!deref_stack_reg(state, ip_p, &state->ip))
 586                         goto err;
 587
 588                 state->ip = unwind_recover_ret_addr(state, state->ip,
 589                                                     (unsigned long *)ip_p);
 590                 state->sp = sp;
 591                 state->regs = NULL;
 592                 state->prev_regs = NULL;
 593                 break;
 594
 595         case ORC_TYPE_REGS:
 596                 if (!deref_stack_regs(state, sp, &state->ip, &state->sp)) {
 597                         orc_warn_current("can't access registers at %pB\n",
 598                                          (void *)orig_ip);
 599                         goto err;
 600                 }
 601                 /*
 602                  * There is a small chance to interrupt at the entry of
 603                  * arch_rethook_trampoline() where the ORC info doesn't exist.
 604                  * That point is right after the RET to arch_rethook_trampoline()
 605                  * which was modified return address.
 606                  * At that point, the @addr_p of the unwind_recover_rethook()
 607                  * (this has to point the address of the stack entry storing
 608                  * the modified return address) must be "SP - (a stack entry)"
 609                  * because SP is incremented by the RET.
 610                  */
 611                 state->ip = unwind_recover_rethook(state, state->ip,
 612                                 (unsigned long *)(state->sp - sizeof(long)));
 613                 state->regs = (struct pt_regs *)sp;
 614                 state->prev_regs = NULL;
 615                 state->full_regs = true;
 616                 break;
 617
 618         case ORC_TYPE_REGS_PARTIAL:
 619                 if (!deref_stack_iret_regs(state, sp, &state->ip, &state->sp)) {
 620                         orc_warn_current("can't access iret registers at %pB\n",
 621                                          (void *)orig_ip);
 622                         goto err;
 623                 }
 624                 /* See ORC_TYPE_REGS case comment. */
 625                 state->ip = unwind_recover_rethook(state, state->ip,
 626                                 (unsigned long *)(state->sp - sizeof(long)));
 627
 628                 if (state->full_regs)
 629                         state->prev_regs = state->regs;
 630                 state->regs = (void *)sp - IRET_FRAME_OFFSET;
 631                 state->full_regs = false;
 632                 break;
 633
 634         default:
 635                 orc_warn("unknown .orc_unwind entry type %d at %pB\n",
 636                          orc->type, (void *)orig_ip);
 637                 goto err;
 638         }
 639
 640         /* Find BP: */
 641         switch (orc->bp_reg) {
 642         case ORC_REG_UNDEFINED:
 643                 if (get_reg(state, offsetof(struct pt_regs, bp), &tmp))
 644                         state->bp = tmp;
 645                 break;
 646
 647         case ORC_REG_PREV_SP:
 648                 if (!deref_stack_reg(state, sp + orc->bp_offset, &state->bp))
 649                         goto err;
 650                 break;
 651
 652         case ORC_REG_BP:
 653                 if (!deref_stack_reg(state, state->bp + orc->bp_offset, &state->bp))
 654                         goto err;
 655                 break;
 656
 657         default:
 658                 orc_warn("unknown BP base reg %d for ip %pB\n",
 659                          orc->bp_reg, (void *)orig_ip);
 660                 goto err;
 661         }
 662
 663         /* Prevent a recursive loop due to bad ORC data: */
 664         if (state->stack_info.type == prev_type &&
 665             on_stack(&state->stack_info, (void *)state->sp, sizeof(long)) &&
 666             state->sp <= prev_sp) {
 667                 orc_warn_current("stack going in the wrong direction? at %pB\n",
 668                                  (void *)orig_ip);
 669                 goto err;
 670         }
 671
 672         preempt_enable();
 673         return true;
 674
 675 err:
 676         state->error = true;
 677
 678 the_end:
 679         preempt_enable();
 680         state->stack_info.type = STACK_TYPE_UNKNOWN;
 681         return false;
 682 }
 683 EXPORT_SYMBOL_GPL(unwind_next_frame);
 684
 685 void __unwind_start(struct unwind_state *state, struct task_struct *task,
 686                     struct pt_regs *regs, unsigned long *first_frame)
 687 {
 688         memset(state, 0, sizeof(*state));
 689         state->task = task;
 690
 691         if (!orc_init)
 692                 goto err;
 693
 694         /*
 695          * Refuse to unwind the stack of a task while it's executing on another
 696          * CPU.  This check is racy, but that's ok: the unwinder has other
 697          * checks to prevent it from going off the rails.
 698          */
 699         if (task_on_another_cpu(task))
 700                 goto err;
 701
 702         if (regs) {
 703                 if (user_mode(regs))
 704                         goto the_end;
 705
 706                 state->ip = regs->ip;
 707                 state->sp = regs->sp;
 708                 state->bp = regs->bp;
 709                 state->regs = regs;
 710                 state->full_regs = true;
 711                 state->signal = true;
 712
 713         } else if (task == current) {
 714                 asm volatile("lea (%%rip), %0\n\t"
 715                              "mov %%rsp, %1\n\t"
 716                              "mov %%rbp, %2\n\t"
 717                              : "=r" (state->ip), "=r" (state->sp),
 718                                "=r" (state->bp));
 719
 720         } else {
 721                 struct inactive_task_frame *frame = (void *)task->thread.sp;
 722
 723                 state->sp = task->thread.sp + sizeof(*frame);
 724                 state->bp = READ_ONCE_NOCHECK(frame->bp);
 725                 state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
 726                 state->signal = (void *)state->ip == ret_from_fork;
 727         }
 728
 729         if (get_stack_info((unsigned long *)state->sp, state->task,
 730                            &state->stack_info, &state->stack_mask)) {
 731                 /*
 732                  * We weren't on a valid stack.  It's possible that
 733                  * we overflowed a valid stack into a guard page.
 734                  * See if the next page up is valid so that we can
 735                  * generate some kind of backtrace if this happens.
 736                  */
 737                 void *next_page = (void *)PAGE_ALIGN((unsigned long)state->sp);
 738                 state->error = true;
 739                 if (get_stack_info(next_page, state->task, &state->stack_info,
 740                                    &state->stack_mask))
 741                         return;
 742         }
 743
 744         /*
 745          * The caller can provide the address of the first frame directly
 746          * (first_frame) or indirectly (regs->sp) to indicate which stack frame
 747          * to start unwinding at.  Skip ahead until we reach it.
 748          */
 749
 750         /* When starting from regs, skip the regs frame: */
 751         if (regs) {
 752                 unwind_next_frame(state);
 753                 return;
 754         }
 755
 756         /* Otherwise, skip ahead to the user-specified starting frame: */
 757         while (!unwind_done(state) &&
 758                (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
 759                         state->sp <= (unsigned long)first_frame))
 760                 unwind_next_frame(state);
 761
 762         return;
 763
 764 err:
 765         state->error = true;
 766 the_end:
 767         state->stack_info.type = STACK_TYPE_UNKNOWN;
 768 }
 769 EXPORT_SYMBOL_GPL(__unwind_start);