root/arch/x86/kernel/unwind_orc.c

DEFINITIONS

1. orc_ip
2. __orc_find
3. orc_module_find
4. orc_module_find
5. orc_ftrace_find
6. orc_ftrace_find
7. orc_find
8. orc_sort_swap
9. orc_sort_cmp
10. unwind_module_init
11. unwind_init
12. unwind_get_return_address
13. unwind_get_return_address_ptr
14. stack_access_ok
15. deref_stack_reg
16. deref_stack_regs
17. deref_stack_iret_regs
18. get_reg
19. unwind_next_frame
20. __unwind_start

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