arch/arm/kernel/unwind.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * arch/arm/kernel/unwind.c
   4  *
   5  * Copyright (C) 2008 ARM Limited
   6  *
   7  * Stack unwinding support for ARM
   8  *
   9  * An ARM EABI version of gcc is required to generate the unwind
  10  * tables. For information about the structure of the unwind tables,
  11  * see "Exception Handling ABI for the ARM Architecture" at:
  12  *
  13  * http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
  14  */
  15
  16 #ifndef __CHECKER__
  17 #if !defined (__ARM_EABI__)
  18 #warning Your compiler does not have EABI support.
  19 #warning    ARM unwind is known to compile only with EABI compilers.
  20 #warning    Change compiler or disable ARM_UNWIND option.
  21 #endif
  22 #endif /* __CHECKER__ */
  23
  24 #include <linux/kernel.h>
  25 #include <linux/init.h>
  26 #include <linux/export.h>
  27 #include <linux/sched.h>
  28 #include <linux/slab.h>
  29 #include <linux/spinlock.h>
  30 #include <linux/list.h>
  31 #include <linux/module.h>
  32
  33 #include <asm/stacktrace.h>
  34 #include <asm/traps.h>
  35 #include <asm/unwind.h>
  36
  37 #include "reboot.h"
  38
  39 /* Dummy functions to avoid linker complaints */
  40 void __aeabi_unwind_cpp_pr0(void)
  41 {
  42 };
  43 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);
  44
  45 void __aeabi_unwind_cpp_pr1(void)
  46 {
  47 };
  48 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);
  49
  50 void __aeabi_unwind_cpp_pr2(void)
  51 {
  52 };
  53 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
  54
  55 struct unwind_ctrl_block {
  56         unsigned long vrs[16];          /* virtual register set */
  57         const unsigned long *insn;      /* pointer to the current instructions word */
  58         unsigned long sp_high;          /* highest value of sp allowed */
  59         unsigned long *lr_addr;         /* address of LR value on the stack */
  60         /*
  61          * 1 : check for stack overflow for each register pop.
  62          * 0 : save overhead if there is plenty of stack remaining.
  63          */
  64         int check_each_pop;
  65         int entries;                    /* number of entries left to interpret */
  66         int byte;                       /* current byte number in the instructions word */
  67 };
  68
  69 enum regs {
  70 #ifdef CONFIG_THUMB2_KERNEL
  71         FP = 7,
  72 #else
  73         FP = 11,
  74 #endif
  75         SP = 13,
  76         LR = 14,
  77         PC = 15
  78 };
  79
  80 extern const struct unwind_idx __start_unwind_idx[];
  81 static const struct unwind_idx *__origin_unwind_idx;
  82 extern const struct unwind_idx __stop_unwind_idx[];
  83
  84 static DEFINE_RAW_SPINLOCK(unwind_lock);
  85 static LIST_HEAD(unwind_tables);
  86
  87 /* Convert a prel31 symbol to an absolute address */
  88 #define prel31_to_addr(ptr)                             \
  89 ({                                                      \
  90         /* sign-extend to 32 bits */                    \
  91         long offset = (((long)*(ptr)) << 1) >> 1;       \
  92         (unsigned long)(ptr) + offset;                  \
  93 })
  94
  95 /*
  96  * Binary search in the unwind index. The entries are
  97  * guaranteed to be sorted in ascending order by the linker.
  98  *
  99  * start = first entry
 100  * origin = first entry with positive offset (or stop if there is no such entry)
 101  * stop - 1 = last entry
 102  */
 103 static const struct unwind_idx *search_index(unsigned long addr,
 104                                        const struct unwind_idx *start,
 105                                        const struct unwind_idx *origin,
 106                                        const struct unwind_idx *stop)
 107 {
 108         unsigned long addr_prel31;
 109
 110         pr_debug("%s(%08lx, %p, %p, %p)\n",
 111                         __func__, addr, start, origin, stop);
 112
 113         /*
 114          * only search in the section with the matching sign. This way the
 115          * prel31 numbers can be compared as unsigned longs.
 116          */
 117         if (addr < (unsigned long)start)
 118                 /* negative offsets: [start; origin) */
 119                 stop = origin;
 120         else
 121                 /* positive offsets: [origin; stop) */
 122                 start = origin;
 123
 124         /* prel31 for address relavive to start */
 125         addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;
 126
 127         while (start < stop - 1) {
 128                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
 129
 130                 /*
 131                  * As addr_prel31 is relative to start an offset is needed to
 132                  * make it relative to mid.
 133                  */
 134                 if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
 135                                 mid->addr_offset)
 136                         stop = mid;
 137                 else {
 138                         /* keep addr_prel31 relative to start */
 139                         addr_prel31 -= ((unsigned long)mid -
 140                                         (unsigned long)start);
 141                         start = mid;
 142                 }
 143         }
 144
 145         if (likely(start->addr_offset <= addr_prel31))
 146                 return start;
 147         else {
 148                 pr_warn("unwind: Unknown symbol address %08lx\n", addr);
 149                 return NULL;
 150         }
 151 }
 152
 153 static const struct unwind_idx *unwind_find_origin(
 154                 const struct unwind_idx *start, const struct unwind_idx *stop)
 155 {
 156         pr_debug("%s(%p, %p)\n", __func__, start, stop);
 157         while (start < stop) {
 158                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
 159
 160                 if (mid->addr_offset >= 0x40000000)
 161                         /* negative offset */
 162                         start = mid + 1;
 163                 else
 164                         /* positive offset */
 165                         stop = mid;
 166         }
 167         pr_debug("%s -> %p\n", __func__, stop);
 168         return stop;
 169 }
 170
 171 static const struct unwind_idx *unwind_find_idx(unsigned long addr)
 172 {
 173         const struct unwind_idx *idx = NULL;
 174         unsigned long flags;
 175
 176         pr_debug("%s(%08lx)\n", __func__, addr);
 177
 178         if (core_kernel_text(addr)) {
 179                 if (unlikely(!__origin_unwind_idx))
 180                         __origin_unwind_idx =
 181                                 unwind_find_origin(__start_unwind_idx,
 182                                                 __stop_unwind_idx);
 183
 184                 /* main unwind table */
 185                 idx = search_index(addr, __start_unwind_idx,
 186                                    __origin_unwind_idx,
 187                                    __stop_unwind_idx);
 188         } else {
 189                 /* module unwind tables */
 190                 struct unwind_table *table;
 191
 192                 raw_spin_lock_irqsave(&unwind_lock, flags);
 193                 list_for_each_entry(table, &unwind_tables, list) {
 194                         if (addr >= table->begin_addr &&
 195                             addr < table->end_addr) {
 196                                 idx = search_index(addr, table->start,
 197                                                    table->origin,
 198                                                    table->stop);
 199                                 /* Move-to-front to exploit common traces */
 200                                 list_move(&table->list, &unwind_tables);
 201                                 break;
 202                         }
 203                 }
 204                 raw_spin_unlock_irqrestore(&unwind_lock, flags);
 205         }
 206
 207         pr_debug("%s: idx = %p\n", __func__, idx);
 208         return idx;
 209 }
 210
 211 static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
 212 {
 213         unsigned long ret;
 214
 215         if (ctrl->entries <= 0) {
 216                 pr_warn("unwind: Corrupt unwind table\n");
 217                 return 0;
 218         }
 219
 220         ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;
 221
 222         if (ctrl->byte == 0) {
 223                 ctrl->insn++;
 224                 ctrl->entries--;
 225                 ctrl->byte = 3;
 226         } else
 227                 ctrl->byte--;
 228
 229         return ret;
 230 }
 231
 232 /* Before poping a register check whether it is feasible or not */
 233 static int unwind_pop_register(struct unwind_ctrl_block *ctrl,
 234                                 unsigned long **vsp, unsigned int reg)
 235 {
 236         if (unlikely(ctrl->check_each_pop))
 237                 if (*vsp >= (unsigned long *)ctrl->sp_high)
 238                         return -URC_FAILURE;
 239
 240         /* Use READ_ONCE_NOCHECK here to avoid this memory access
 241          * from being tracked by KASAN.
 242          */
 243         ctrl->vrs[reg] = READ_ONCE_NOCHECK(*(*vsp));
 244         if (reg == 14)
 245                 ctrl->lr_addr = *vsp;
 246         (*vsp)++;
 247         return URC_OK;
 248 }
 249
 250 /* Helper functions to execute the instructions */
 251 static int unwind_exec_pop_subset_r4_to_r13(struct unwind_ctrl_block *ctrl,
 252                                                 unsigned long mask)
 253 {
 254         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
 255         int load_sp, reg = 4;
 256
 257         load_sp = mask & (1 << (13 - 4));
 258         while (mask) {
 259                 if (mask & 1)
 260                         if (unwind_pop_register(ctrl, &vsp, reg))
 261                                 return -URC_FAILURE;
 262                 mask >>= 1;
 263                 reg++;
 264         }
 265         if (!load_sp) {
 266                 ctrl->vrs[SP] = (unsigned long)vsp;
 267         }
 268
 269         return URC_OK;
 270 }
 271
 272 static int unwind_exec_pop_r4_to_rN(struct unwind_ctrl_block *ctrl,
 273                                         unsigned long insn)
 274 {
 275         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
 276         int reg;
 277
 278         /* pop R4-R[4+bbb] */
 279         for (reg = 4; reg <= 4 + (insn & 7); reg++)
 280                 if (unwind_pop_register(ctrl, &vsp, reg))
 281                                 return -URC_FAILURE;
 282
 283         if (insn & 0x8)
 284                 if (unwind_pop_register(ctrl, &vsp, 14))
 285                                 return -URC_FAILURE;
 286
 287         ctrl->vrs[SP] = (unsigned long)vsp;
 288
 289         return URC_OK;
 290 }
 291
 292 static int unwind_exec_pop_subset_r0_to_r3(struct unwind_ctrl_block *ctrl,
 293                                                 unsigned long mask)
 294 {
 295         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
 296         int reg = 0;
 297
 298         /* pop R0-R3 according to mask */
 299         while (mask) {
 300                 if (mask & 1)
 301                         if (unwind_pop_register(ctrl, &vsp, reg))
 302                                 return -URC_FAILURE;
 303                 mask >>= 1;
 304                 reg++;
 305         }
 306         ctrl->vrs[SP] = (unsigned long)vsp;
 307
 308         return URC_OK;
 309 }
 310
 311 static unsigned long unwind_decode_uleb128(struct unwind_ctrl_block *ctrl)
 312 {
 313         unsigned long bytes = 0;
 314         unsigned long insn;
 315         unsigned long result = 0;
 316
 317         /*
 318          * unwind_get_byte() will advance `ctrl` one instruction at a time, so
 319          * loop until we get an instruction byte where bit 7 is not set.
 320          *
 321          * Note: This decodes a maximum of 4 bytes to output 28 bits data where
 322          * max is 0xfffffff: that will cover a vsp increment of 1073742336, hence
 323          * it is sufficient for unwinding the stack.
 324          */
 325         do {
 326                 insn = unwind_get_byte(ctrl);
 327                 result |= (insn & 0x7f) << (bytes * 7);
 328                 bytes++;
 329         } while (!!(insn & 0x80) && (bytes != sizeof(result)));
 330
 331         return result;
 332 }
 333
 334 /*
 335  * Execute the current unwind instruction.
 336  */
 337 static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
 338 {
 339         unsigned long insn = unwind_get_byte(ctrl);
 340         int ret = URC_OK;
 341
 342         pr_debug("%s: insn = %08lx\n", __func__, insn);
 343
 344         if ((insn & 0xc0) == 0x00)
 345                 ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
 346         else if ((insn & 0xc0) == 0x40) {
 347                 ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
 348         } else if ((insn & 0xf0) == 0x80) {
 349                 unsigned long mask;
 350
 351                 insn = (insn << 8) | unwind_get_byte(ctrl);
 352                 mask = insn & 0x0fff;
 353                 if (mask == 0) {
 354                         pr_warn("unwind: 'Refuse to unwind' instruction %04lx\n",
 355                                 insn);
 356                         return -URC_FAILURE;
 357                 }
 358
 359                 ret = unwind_exec_pop_subset_r4_to_r13(ctrl, mask);
 360                 if (ret)
 361                         goto error;
 362         } else if ((insn & 0xf0) == 0x90 &&
 363                    (insn & 0x0d) != 0x0d) {
 364                 ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
 365         } else if ((insn & 0xf0) == 0xa0) {
 366                 ret = unwind_exec_pop_r4_to_rN(ctrl, insn);
 367                 if (ret)
 368                         goto error;
 369         } else if (insn == 0xb0) {
 370                 if (ctrl->vrs[PC] == 0)
 371                         ctrl->vrs[PC] = ctrl->vrs[LR];
 372                 /* no further processing */
 373                 ctrl->entries = 0;
 374         } else if (insn == 0xb1) {
 375                 unsigned long mask = unwind_get_byte(ctrl);
 376
 377                 if (mask == 0 || mask & 0xf0) {
 378                         pr_warn("unwind: Spare encoding %04lx\n",
 379                                 (insn << 8) | mask);
 380                         return -URC_FAILURE;
 381                 }
 382
 383                 ret = unwind_exec_pop_subset_r0_to_r3(ctrl, mask);
 384                 if (ret)
 385                         goto error;
 386         } else if (insn == 0xb2) {
 387                 unsigned long uleb128 = unwind_decode_uleb128(ctrl);
 388
 389                 ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
 390         } else {
 391                 pr_warn("unwind: Unhandled instruction %02lx\n", insn);
 392                 return -URC_FAILURE;
 393         }
 394
 395         pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
 396                  ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);
 397
 398 error:
 399         return ret;
 400 }
 401
 402 /*
 403  * Unwind a single frame starting with *sp for the symbol at *pc. It
 404  * updates the *pc and *sp with the new values.
 405  */
 406 int unwind_frame(struct stackframe *frame)
 407 {
 408         const struct unwind_idx *idx;
 409         struct unwind_ctrl_block ctrl;
 410         unsigned long sp_low;
 411
 412         /* store the highest address on the stack to avoid crossing it*/
 413         sp_low = frame->sp;
 414         ctrl.sp_high = ALIGN(sp_low - THREAD_SIZE, THREAD_ALIGN)
 415                        + THREAD_SIZE;
 416
 417         pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
 418                  frame->pc, frame->lr, frame->sp);
 419
 420         idx = unwind_find_idx(frame->pc);
 421         if (!idx) {
 422                 if (frame->pc && kernel_text_address(frame->pc)) {
 423                         if (in_module_plt(frame->pc) && frame->pc != frame->lr) {
 424                                 /*
 425                                  * Quoting Ard: Veneers only set PC using a
 426                                  * PC+immediate LDR, and so they don't affect
 427                                  * the state of the stack or the register file
 428                                  */
 429                                 frame->pc = frame->lr;
 430                                 return URC_OK;
 431                         }
 432                         pr_warn("unwind: Index not found %08lx\n", frame->pc);
 433                 }
 434                 return -URC_FAILURE;
 435         }
 436
 437         ctrl.vrs[FP] = frame->fp;
 438         ctrl.vrs[SP] = frame->sp;
 439         ctrl.vrs[LR] = frame->lr;
 440         ctrl.vrs[PC] = 0;
 441
 442         if (idx->insn == 1)
 443                 /* can't unwind */
 444                 return -URC_FAILURE;
 445         else if (frame->pc == prel31_to_addr(&idx->addr_offset)) {
 446                 /*
 447                  * Unwinding is tricky when we're halfway through the prologue,
 448                  * since the stack frame that the unwinder expects may not be
 449                  * fully set up yet. However, one thing we do know for sure is
 450                  * that if we are unwinding from the very first instruction of
 451                  * a function, we are still effectively in the stack frame of
 452                  * the caller, and the unwind info has no relevance yet.
 453                  */
 454                 if (frame->pc == frame->lr)
 455                         return -URC_FAILURE;
 456                 frame->pc = frame->lr;
 457                 return URC_OK;
 458         } else if ((idx->insn & 0x80000000) == 0)
 459                 /* prel31 to the unwind table */
 460                 ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
 461         else if ((idx->insn & 0xff000000) == 0x80000000)
 462                 /* only personality routine 0 supported in the index */
 463                 ctrl.insn = &idx->insn;
 464         else {
 465                 pr_warn("unwind: Unsupported personality routine %08lx in the index at %p\n",
 466                         idx->insn, idx);
 467                 return -URC_FAILURE;
 468         }
 469
 470         /* check the personality routine */
 471         if ((*ctrl.insn & 0xff000000) == 0x80000000) {
 472                 ctrl.byte = 2;
 473                 ctrl.entries = 1;
 474         } else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
 475                 ctrl.byte = 1;
 476                 ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
 477         } else {
 478                 pr_warn("unwind: Unsupported personality routine %08lx at %p\n",
 479                         *ctrl.insn, ctrl.insn);
 480                 return -URC_FAILURE;
 481         }
 482
 483         ctrl.check_each_pop = 0;
 484
 485         if (prel31_to_addr(&idx->addr_offset) == (u32)&call_with_stack) {
 486                 /*
 487                  * call_with_stack() is the only place where we permit SP to
 488                  * jump from one stack to another, and since we know it is
 489                  * guaranteed to happen, set up the SP bounds accordingly.
 490                  */
 491                 sp_low = frame->fp;
 492                 ctrl.sp_high = ALIGN(frame->fp, THREAD_SIZE);
 493         }
 494
 495         while (ctrl.entries > 0) {
 496                 int urc;
 497                 if ((ctrl.sp_high - ctrl.vrs[SP]) < sizeof(ctrl.vrs))
 498                         ctrl.check_each_pop = 1;
 499                 urc = unwind_exec_insn(&ctrl);
 500                 if (urc < 0)
 501                         return urc;
 502                 if (ctrl.vrs[SP] < sp_low || ctrl.vrs[SP] > ctrl.sp_high)
 503                         return -URC_FAILURE;
 504         }
 505
 506         if (ctrl.vrs[PC] == 0)
 507                 ctrl.vrs[PC] = ctrl.vrs[LR];
 508
 509         /* check for infinite loop */
 510         if (frame->pc == ctrl.vrs[PC] && frame->sp == ctrl.vrs[SP])
 511                 return -URC_FAILURE;
 512
 513         frame->fp = ctrl.vrs[FP];
 514         frame->sp = ctrl.vrs[SP];
 515         frame->lr = ctrl.vrs[LR];
 516         frame->pc = ctrl.vrs[PC];
 517         frame->lr_addr = ctrl.lr_addr;
 518
 519         return URC_OK;
 520 }
 521
 522 void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 523                       const char *loglvl)
 524 {
 525         struct stackframe frame;
 526
 527         printk("%sCall trace: ", loglvl);
 528
 529         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 530
 531         if (!tsk)
 532                 tsk = current;
 533
 534         if (regs) {
 535                 arm_get_current_stackframe(regs, &frame);
 536                 /* PC might be corrupted, use LR in that case. */
 537                 if (!kernel_text_address(regs->ARM_pc))
 538                         frame.pc = regs->ARM_lr;
 539         } else if (tsk == current) {
 540                 frame.fp = (unsigned long)__builtin_frame_address(0);
 541                 frame.sp = current_stack_pointer;
 542                 frame.lr = (unsigned long)__builtin_return_address(0);
 543                 /* We are saving the stack and execution state at this
 544                  * point, so we should ensure that frame.pc is within
 545                  * this block of code.
 546                  */
 547 here:
 548                 frame.pc = (unsigned long)&&here;
 549         } else {
 550                 /* task blocked in __switch_to */
 551                 frame.fp = thread_saved_fp(tsk);
 552                 frame.sp = thread_saved_sp(tsk);
 553                 /*
 554                  * The function calling __switch_to cannot be a leaf function
 555                  * so LR is recovered from the stack.
 556                  */
 557                 frame.lr = 0;
 558                 frame.pc = thread_saved_pc(tsk);
 559         }
 560
 561         while (1) {
 562                 int urc;
 563                 unsigned long where = frame.pc;
 564
 565                 urc = unwind_frame(&frame);
 566                 if (urc < 0)
 567                         break;
 568                 dump_backtrace_entry(where, frame.pc, frame.sp - 4, loglvl);
 569         }
 570 }
 571
 572 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
 573                                       unsigned long text_addr,
 574                                       unsigned long text_size)
 575 {
 576         unsigned long flags;
 577         struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
 578
 579         pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
 580                  text_addr, text_size);
 581
 582         if (!tab)
 583                 return tab;
 584
 585         tab->start = (const struct unwind_idx *)start;
 586         tab->stop = (const struct unwind_idx *)(start + size);
 587         tab->origin = unwind_find_origin(tab->start, tab->stop);
 588         tab->begin_addr = text_addr;
 589         tab->end_addr = text_addr + text_size;
 590
 591         raw_spin_lock_irqsave(&unwind_lock, flags);
 592         list_add_tail(&tab->list, &unwind_tables);
 593         raw_spin_unlock_irqrestore(&unwind_lock, flags);
 594
 595         return tab;
 596 }
 597
 598 void unwind_table_del(struct unwind_table *tab)
 599 {
 600         unsigned long flags;
 601
 602         if (!tab)
 603                 return;
 604
 605         raw_spin_lock_irqsave(&unwind_lock, flags);
 606         list_del(&tab->list);
 607         raw_spin_unlock_irqrestore(&unwind_lock, flags);
 608
 609         kfree(tab);
 610 }