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Linux/arch/arm/kernel/unwind.c

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  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 #elif (__GNUC__ == 4 && __GNUC_MINOR__ <= 2) && !defined(__clang__)
 22 #warning Your compiler is too buggy; it is known to not compile ARM unwind support.
 23 #warning    Change compiler or disable ARM_UNWIND option.
 24 #endif
 25 #endif /* __CHECKER__ */
 26 
 27 #include <linux/kernel.h>
 28 #include <linux/init.h>
 29 #include <linux/export.h>
 30 #include <linux/sched.h>
 31 #include <linux/slab.h>
 32 #include <linux/spinlock.h>
 33 #include <linux/list.h>
 34 
 35 #include <asm/stacktrace.h>
 36 #include <asm/traps.h>
 37 #include <asm/unwind.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         /*
 60          * 1 : check for stack overflow for each register pop.
 61          * 0 : save overhead if there is plenty of stack remaining.
 62          */
 63         int check_each_pop;
 64         int entries;                    /* number of entries left to interpret */
 65         int byte;                       /* current byte number in the instructions word */
 66 };
 67 
 68 enum regs {
 69 #ifdef CONFIG_THUMB2_KERNEL
 70         FP = 7,
 71 #else
 72         FP = 11,
 73 #endif
 74         SP = 13,
 75         LR = 14,
 76         PC = 15
 77 };
 78 
 79 extern const struct unwind_idx __start_unwind_idx[];
 80 static const struct unwind_idx *__origin_unwind_idx;
 81 extern const struct unwind_idx __stop_unwind_idx[];
 82 
 83 static DEFINE_RAW_SPINLOCK(unwind_lock);
 84 static LIST_HEAD(unwind_tables);
 85 
 86 /* Convert a prel31 symbol to an absolute address */
 87 #define prel31_to_addr(ptr)                             \
 88 ({                                                      \
 89         /* sign-extend to 32 bits */                    \
 90         long offset = (((long)*(ptr)) << 1) >> 1;       \
 91         (unsigned long)(ptr) + offset;                  \
 92 })
 93 
 94 /*
 95  * Binary search in the unwind index. The entries are
 96  * guaranteed to be sorted in ascending order by the linker.
 97  *
 98  * start = first entry
 99  * origin = first entry with positive offset (or stop if there is no such entry)
100  * stop - 1 = last entry
101  */
102 static const struct unwind_idx *search_index(unsigned long addr,
103                                        const struct unwind_idx *start,
104                                        const struct unwind_idx *origin,
105                                        const struct unwind_idx *stop)
106 {
107         unsigned long addr_prel31;
108 
109         pr_debug("%s(%08lx, %p, %p, %p)\n",
110                         __func__, addr, start, origin, stop);
111 
112         /*
113          * only search in the section with the matching sign. This way the
114          * prel31 numbers can be compared as unsigned longs.
115          */
116         if (addr < (unsigned long)start)
117                 /* negative offsets: [start; origin) */
118                 stop = origin;
119         else
120                 /* positive offsets: [origin; stop) */
121                 start = origin;
122 
123         /* prel31 for address relavive to start */
124         addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;
125 
126         while (start < stop - 1) {
127                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
128 
129                 /*
130                  * As addr_prel31 is relative to start an offset is needed to
131                  * make it relative to mid.
132                  */
133                 if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
134                                 mid->addr_offset)
135                         stop = mid;
136                 else {
137                         /* keep addr_prel31 relative to start */
138                         addr_prel31 -= ((unsigned long)mid -
139                                         (unsigned long)start);
140                         start = mid;
141                 }
142         }
143 
144         if (likely(start->addr_offset <= addr_prel31))
145                 return start;
146         else {
147                 pr_warn("unwind: Unknown symbol address %08lx\n", addr);
148                 return NULL;
149         }
150 }
151 
152 static const struct unwind_idx *unwind_find_origin(
153                 const struct unwind_idx *start, const struct unwind_idx *stop)
154 {
155         pr_debug("%s(%p, %p)\n", __func__, start, stop);
156         while (start < stop) {
157                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
158 
159                 if (mid->addr_offset >= 0x40000000)
160                         /* negative offset */
161                         start = mid + 1;
162                 else
163                         /* positive offset */
164                         stop = mid;
165         }
166         pr_debug("%s -> %p\n", __func__, stop);
167         return stop;
168 }
169 
170 static const struct unwind_idx *unwind_find_idx(unsigned long addr)
171 {
172         const struct unwind_idx *idx = NULL;
173         unsigned long flags;
174 
175         pr_debug("%s(%08lx)\n", __func__, addr);
176 
177         if (core_kernel_text(addr)) {
178                 if (unlikely(!__origin_unwind_idx))
179                         __origin_unwind_idx =
180                                 unwind_find_origin(__start_unwind_idx,
181                                                 __stop_unwind_idx);
182 
183                 /* main unwind table */
184                 idx = search_index(addr, __start_unwind_idx,
185                                    __origin_unwind_idx,
186                                    __stop_unwind_idx);
187         } else {
188                 /* module unwind tables */
189                 struct unwind_table *table;
190 
191                 raw_spin_lock_irqsave(&unwind_lock, flags);
192                 list_for_each_entry(table, &unwind_tables, list) {
193                         if (addr >= table->begin_addr &&
194                             addr < table->end_addr) {
195                                 idx = search_index(addr, table->start,
196                                                    table->origin,
197                                                    table->stop);
198                                 /* Move-to-front to exploit common traces */
199                                 list_move(&table->list, &unwind_tables);
200                                 break;
201                         }
202                 }
203                 raw_spin_unlock_irqrestore(&unwind_lock, flags);
204         }
205 
206         pr_debug("%s: idx = %p\n", __func__, idx);
207         return idx;
208 }
209 
210 static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
211 {
212         unsigned long ret;
213 
214         if (ctrl->entries <= 0) {
215                 pr_warn("unwind: Corrupt unwind table\n");
216                 return 0;
217         }
218 
219         ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;
220 
221         if (ctrl->byte == 0) {
222                 ctrl->insn++;
223                 ctrl->entries--;
224                 ctrl->byte = 3;
225         } else
226                 ctrl->byte--;
227 
228         return ret;
229 }
230 
231 /* Before poping a register check whether it is feasible or not */
232 static int unwind_pop_register(struct unwind_ctrl_block *ctrl,
233                                 unsigned long **vsp, unsigned int reg)
234 {
235         if (unlikely(ctrl->check_each_pop))
236                 if (*vsp >= (unsigned long *)ctrl->sp_high)
237                         return -URC_FAILURE;
238 
239         ctrl->vrs[reg] = *(*vsp)++;
240         return URC_OK;
241 }
242 
243 /* Helper functions to execute the instructions */
244 static int unwind_exec_pop_subset_r4_to_r13(struct unwind_ctrl_block *ctrl,
245                                                 unsigned long mask)
246 {
247         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
248         int load_sp, reg = 4;
249 
250         load_sp = mask & (1 << (13 - 4));
251         while (mask) {
252                 if (mask & 1)
253                         if (unwind_pop_register(ctrl, &vsp, reg))
254                                 return -URC_FAILURE;
255                 mask >>= 1;
256                 reg++;
257         }
258         if (!load_sp)
259                 ctrl->vrs[SP] = (unsigned long)vsp;
260 
261         return URC_OK;
262 }
263 
264 static int unwind_exec_pop_r4_to_rN(struct unwind_ctrl_block *ctrl,
265                                         unsigned long insn)
266 {
267         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
268         int reg;
269 
270         /* pop R4-R[4+bbb] */
271         for (reg = 4; reg <= 4 + (insn & 7); reg++)
272                 if (unwind_pop_register(ctrl, &vsp, reg))
273                                 return -URC_FAILURE;
274 
275         if (insn & 0x8)
276                 if (unwind_pop_register(ctrl, &vsp, 14))
277                                 return -URC_FAILURE;
278 
279         ctrl->vrs[SP] = (unsigned long)vsp;
280 
281         return URC_OK;
282 }
283 
284 static int unwind_exec_pop_subset_r0_to_r3(struct unwind_ctrl_block *ctrl,
285                                                 unsigned long mask)
286 {
287         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
288         int reg = 0;
289 
290         /* pop R0-R3 according to mask */
291         while (mask) {
292                 if (mask & 1)
293                         if (unwind_pop_register(ctrl, &vsp, reg))
294                                 return -URC_FAILURE;
295                 mask >>= 1;
296                 reg++;
297         }
298         ctrl->vrs[SP] = (unsigned long)vsp;
299 
300         return URC_OK;
301 }
302 
303 /*
304  * Execute the current unwind instruction.
305  */
306 static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
307 {
308         unsigned long insn = unwind_get_byte(ctrl);
309         int ret = URC_OK;
310 
311         pr_debug("%s: insn = %08lx\n", __func__, insn);
312 
313         if ((insn & 0xc0) == 0x00)
314                 ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
315         else if ((insn & 0xc0) == 0x40)
316                 ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
317         else if ((insn & 0xf0) == 0x80) {
318                 unsigned long mask;
319 
320                 insn = (insn << 8) | unwind_get_byte(ctrl);
321                 mask = insn & 0x0fff;
322                 if (mask == 0) {
323                         pr_warn("unwind: 'Refuse to unwind' instruction %04lx\n",
324                                 insn);
325                         return -URC_FAILURE;
326                 }
327 
328                 ret = unwind_exec_pop_subset_r4_to_r13(ctrl, mask);
329                 if (ret)
330                         goto error;
331         } else if ((insn & 0xf0) == 0x90 &&
332                    (insn & 0x0d) != 0x0d)
333                 ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
334         else if ((insn & 0xf0) == 0xa0) {
335                 ret = unwind_exec_pop_r4_to_rN(ctrl, insn);
336                 if (ret)
337                         goto error;
338         } else if (insn == 0xb0) {
339                 if (ctrl->vrs[PC] == 0)
340                         ctrl->vrs[PC] = ctrl->vrs[LR];
341                 /* no further processing */
342                 ctrl->entries = 0;
343         } else if (insn == 0xb1) {
344                 unsigned long mask = unwind_get_byte(ctrl);
345 
346                 if (mask == 0 || mask & 0xf0) {
347                         pr_warn("unwind: Spare encoding %04lx\n",
348                                 (insn << 8) | mask);
349                         return -URC_FAILURE;
350                 }
351 
352                 ret = unwind_exec_pop_subset_r0_to_r3(ctrl, mask);
353                 if (ret)
354                         goto error;
355         } else if (insn == 0xb2) {
356                 unsigned long uleb128 = unwind_get_byte(ctrl);
357 
358                 ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
359         } else {
360                 pr_warn("unwind: Unhandled instruction %02lx\n", insn);
361                 return -URC_FAILURE;
362         }
363 
364         pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
365                  ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);
366 
367 error:
368         return ret;
369 }
370 
371 /*
372  * Unwind a single frame starting with *sp for the symbol at *pc. It
373  * updates the *pc and *sp with the new values.
374  */
375 int unwind_frame(struct stackframe *frame)
376 {
377         unsigned long low;
378         const struct unwind_idx *idx;
379         struct unwind_ctrl_block ctrl;
380 
381         /* store the highest address on the stack to avoid crossing it*/
382         low = frame->sp;
383         ctrl.sp_high = ALIGN(low, THREAD_SIZE);
384 
385         pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
386                  frame->pc, frame->lr, frame->sp);
387 
388         if (!kernel_text_address(frame->pc))
389                 return -URC_FAILURE;
390 
391         idx = unwind_find_idx(frame->pc);
392         if (!idx) {
393                 pr_warn("unwind: Index not found %08lx\n", frame->pc);
394                 return -URC_FAILURE;
395         }
396 
397         ctrl.vrs[FP] = frame->fp;
398         ctrl.vrs[SP] = frame->sp;
399         ctrl.vrs[LR] = frame->lr;
400         ctrl.vrs[PC] = 0;
401 
402         if (idx->insn == 1)
403                 /* can't unwind */
404                 return -URC_FAILURE;
405         else if ((idx->insn & 0x80000000) == 0)
406                 /* prel31 to the unwind table */
407                 ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
408         else if ((idx->insn & 0xff000000) == 0x80000000)
409                 /* only personality routine 0 supported in the index */
410                 ctrl.insn = &idx->insn;
411         else {
412                 pr_warn("unwind: Unsupported personality routine %08lx in the index at %p\n",
413                         idx->insn, idx);
414                 return -URC_FAILURE;
415         }
416 
417         /* check the personality routine */
418         if ((*ctrl.insn & 0xff000000) == 0x80000000) {
419                 ctrl.byte = 2;
420                 ctrl.entries = 1;
421         } else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
422                 ctrl.byte = 1;
423                 ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
424         } else {
425                 pr_warn("unwind: Unsupported personality routine %08lx at %p\n",
426                         *ctrl.insn, ctrl.insn);
427                 return -URC_FAILURE;
428         }
429 
430         ctrl.check_each_pop = 0;
431 
432         while (ctrl.entries > 0) {
433                 int urc;
434                 if ((ctrl.sp_high - ctrl.vrs[SP]) < sizeof(ctrl.vrs))
435                         ctrl.check_each_pop = 1;
436                 urc = unwind_exec_insn(&ctrl);
437                 if (urc < 0)
438                         return urc;
439                 if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= ctrl.sp_high)
440                         return -URC_FAILURE;
441         }
442 
443         if (ctrl.vrs[PC] == 0)
444                 ctrl.vrs[PC] = ctrl.vrs[LR];
445 
446         /* check for infinite loop */
447         if (frame->pc == ctrl.vrs[PC] && frame->sp == ctrl.vrs[SP])
448                 return -URC_FAILURE;
449 
450         frame->fp = ctrl.vrs[FP];
451         frame->sp = ctrl.vrs[SP];
452         frame->lr = ctrl.vrs[LR];
453         frame->pc = ctrl.vrs[PC];
454 
455         return URC_OK;
456 }
457 
458 void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk,
459                       const char *loglvl)
460 {
461         struct stackframe frame;
462 
463         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
464 
465         if (!tsk)
466                 tsk = current;
467 
468         if (regs) {
469                 arm_get_current_stackframe(regs, &frame);
470                 /* PC might be corrupted, use LR in that case. */
471                 if (!kernel_text_address(regs->ARM_pc))
472                         frame.pc = regs->ARM_lr;
473         } else if (tsk == current) {
474                 frame.fp = (unsigned long)__builtin_frame_address(0);
475                 frame.sp = current_stack_pointer;
476                 frame.lr = (unsigned long)__builtin_return_address(0);
477                 frame.pc = (unsigned long)unwind_backtrace;
478         } else {
479                 /* task blocked in __switch_to */
480                 frame.fp = thread_saved_fp(tsk);
481                 frame.sp = thread_saved_sp(tsk);
482                 /*
483                  * The function calling __switch_to cannot be a leaf function
484                  * so LR is recovered from the stack.
485                  */
486                 frame.lr = 0;
487                 frame.pc = thread_saved_pc(tsk);
488         }
489 
490         while (1) {
491                 int urc;
492                 unsigned long where = frame.pc;
493 
494                 urc = unwind_frame(&frame);
495                 if (urc < 0)
496                         break;
497                 dump_backtrace_entry(where, frame.pc, frame.sp - 4, loglvl);
498         }
499 }
500 
501 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
502                                       unsigned long text_addr,
503                                       unsigned long text_size)
504 {
505         unsigned long flags;
506         struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
507 
508         pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
509                  text_addr, text_size);
510 
511         if (!tab)
512                 return tab;
513 
514         tab->start = (const struct unwind_idx *)start;
515         tab->stop = (const struct unwind_idx *)(start + size);
516         tab->origin = unwind_find_origin(tab->start, tab->stop);
517         tab->begin_addr = text_addr;
518         tab->end_addr = text_addr + text_size;
519 
520         raw_spin_lock_irqsave(&unwind_lock, flags);
521         list_add_tail(&tab->list, &unwind_tables);
522         raw_spin_unlock_irqrestore(&unwind_lock, flags);
523 
524         return tab;
525 }
526 
527 void unwind_table_del(struct unwind_table *tab)
528 {
529         unsigned long flags;
530 
531         if (!tab)
532                 return;
533 
534         raw_spin_lock_irqsave(&unwind_lock, flags);
535         list_del(&tab->list);
536         raw_spin_unlock_irqrestore(&unwind_lock, flags);
537 
538         kfree(tab);
539 }
540 

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