1 /*
2 * Copyright 2013-2014 Andrew Turner.
3 * Copyright 2013-2014 Ian Lepore.
4 * Copyright 2013-2014 Rui Paulo.
5 * Copyright 2013 Eitan Adler.
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions are
10 * met:
11 *
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
21 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE
22 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
23 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
24 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
25 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
26 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
27 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
28 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31 #include <sys/param.h>
32 #include <sys/kernel.h>
33 #include <sys/linker.h>
34 #include <sys/malloc.h>
35 #include <sys/proc.h>
36 #include <sys/queue.h>
37 #include <sys/systm.h>
38
39 #include <machine/machdep.h>
40 #include <machine/stack.h>
41
42 #include "linker_if.h"
43
44 /*
45 * Definitions for the instruction interpreter.
46 *
47 * The ARM EABI specifies how to perform the frame unwinding in the
48 * Exception Handling ABI for the ARM Architecture document. To perform
49 * the unwind we need to know the initial frame pointer, stack pointer,
50 * link register and program counter. We then find the entry within the
51 * index table that points to the function the program counter is within.
52 * This gives us either a list of three instructions to process, a 31-bit
53 * relative offset to a table of instructions, or a value telling us
54 * we can't unwind any further.
55 *
56 * When we have the instructions to process we need to decode them
57 * following table 4 in section 9.3. This describes a collection of bit
58 * patterns to encode that steps to take to update the stack pointer and
59 * link register to the correct values at the start of the function.
60 */
61
62 /* A special case when we are unable to unwind past this function */
63 #define EXIDX_CANTUNWIND 1
64
65 /*
66 * Entry types.
67 * These are the only entry types that have been seen in the kernel.
68 */
69 #define ENTRY_MASK 0xff000000
70 #define ENTRY_ARM_SU16 0x80000000
71 #define ENTRY_ARM_LU16 0x81000000
72
73 /* Instruction masks. */
74 #define INSN_VSP_MASK 0xc0
75 #define INSN_VSP_SIZE_MASK 0x3f
76 #define INSN_STD_MASK 0xf0
77 #define INSN_STD_DATA_MASK 0x0f
78 #define INSN_POP_TYPE_MASK 0x08
79 #define INSN_POP_COUNT_MASK 0x07
80 #define INSN_VSP_LARGE_INC_MASK 0xff
81
82 /* Instruction definitions */
83 #define INSN_VSP_INC 0x00
84 #define INSN_VSP_DEC 0x40
85 #define INSN_POP_MASKED 0x80
86 #define INSN_VSP_REG 0x90
87 #define INSN_POP_COUNT 0xa0
88 #define INSN_FINISH 0xb0
89 #define INSN_POP_REGS 0xb1
90 #define INSN_VSP_LARGE_INC 0xb2
91
92 /* An item in the exception index table */
93 struct unwind_idx {
94 uint32_t offset;
95 uint32_t insn;
96 };
97
98 /*
99 * Local cache of unwind info for loaded modules.
100 *
101 * To unwind the stack through the code in a loaded module, we need to access
102 * the module's exidx unwind data. To locate that data, one must search the
103 * elf section headers for the SHT_ARM_EXIDX section. Those headers are
104 * available at the time the module is being loaded, but are discarded by time
105 * the load process has completed. Code in kern/link_elf.c locates the data we
106 * need and stores it into the linker_file structure before calling the arm
107 * machdep routine for handling loaded modules (in arm/elf_machdep.c). That
108 * function calls into this code to pass along the unwind info, which we save
109 * into one of these module_info structures.
110 *
111 * Because we have to help stack(9) gather stack info at any time, including in
112 * contexts where sleeping is not allowed, we cannot use linker_file_foreach()
113 * to walk the kernel's list of linker_file structs, because doing so requires
114 * acquiring an exclusive sx_lock. So instead, we keep a local list of these
115 * structures, one for each loaded module (and one for the kernel itself that we
116 * synthesize at init time). New entries are added to the end of this list as
117 * needed, but entries are never deleted from the list. Instead, they are
118 * cleared out in-place to mark them as unused. That means the code doing stack
119 * unwinding can always safely walk the list without locking, because the
120 * structure of the list never changes in a way that would cause the walker to
121 * follow a bad link.
122 *
123 * A cleared-out entry on the list has module start=UINTPTR_MAX and end=0, so
124 * start <= addr < end cannot be true for any value of addr being searched for.
125 * We also don't have to worry about races where we look up the unwind info just
126 * before a module is unloaded and try to access it concurrently with or just
127 * after the unloading happens in another thread, because that means the path of
128 * execution leads through a now-unloaded module, and that's already well into
129 * undefined-behavior territory.
130 *
131 * List entries marked as unused get reused when new modules are loaded. We
132 * don't worry about holding a few unused bytes of memory in the list after
133 * unloading a module.
134 */
135 struct module_info {
136 uintptr_t module_start; /* Start of loaded module */
137 uintptr_t module_end; /* End of loaded module */
138 uintptr_t exidx_start; /* Start of unwind data */
139 uintptr_t exidx_end; /* End of unwind data */
140 STAILQ_ENTRY(module_info)
141 link; /* Link to next entry */
142 };
143 static STAILQ_HEAD(, module_info) module_list;
144
145 /*
146 * Hide ugly casting in somewhat-less-ugly macros.
147 * CADDR - cast a pointer or number to caddr_t.
148 * UADDR - cast a pointer or number to uintptr_t.
149 */
150 #define CADDR(addr) ((caddr_t)(void*)(uintptr_t)(addr))
151 #define UADDR(addr) ((uintptr_t)(addr))
152
153 /*
154 * Clear the info in an existing module_info entry on the list. The
155 * module_start/end addresses are set to values that cannot match any real
156 * memory address. The entry remains on the list, but will be ignored until it
157 * is populated with new data.
158 */
159 static void
clear_module_info(struct module_info * info)160 clear_module_info(struct module_info *info)
161 {
162 info->module_start = UINTPTR_MAX;
163 info->module_end = 0;
164 }
165
166 /*
167 * Populate an existing module_info entry (which is already on the list) with
168 * the info for a new module.
169 */
170 static void
populate_module_info(struct module_info * info,linker_file_t lf)171 populate_module_info(struct module_info *info, linker_file_t lf)
172 {
173
174 /*
175 * Careful! The module_start and module_end fields must not be set
176 * until all other data in the structure is valid.
177 */
178 info->exidx_start = UADDR(lf->exidx_addr);
179 info->exidx_end = UADDR(lf->exidx_addr) + lf->exidx_size;
180 info->module_start = UADDR(lf->address);
181 info->module_end = UADDR(lf->address) + lf->size;
182 }
183
184 /*
185 * Create a new empty module_info entry and add it to the tail of the list.
186 */
187 static struct module_info *
create_module_info(void)188 create_module_info(void)
189 {
190 struct module_info *info;
191
192 info = malloc(sizeof(*info), M_CACHE, M_WAITOK | M_ZERO);
193 clear_module_info(info);
194 STAILQ_INSERT_TAIL(&module_list, info, link);
195 return (info);
196 }
197
198 /*
199 * Search for a module_info entry on the list whose address range contains the
200 * given address. If the search address is zero (no module will be loaded at
201 * zero), then we're looking for an empty item to reuse, which is indicated by
202 * module_start being set to UINTPTR_MAX in the entry.
203 */
204 static struct module_info *
find_module_info(uintptr_t addr)205 find_module_info(uintptr_t addr)
206 {
207 struct module_info *info;
208
209 STAILQ_FOREACH(info, &module_list, link) {
210 if ((addr >= info->module_start && addr < info->module_end) ||
211 (addr == 0 && info->module_start == UINTPTR_MAX))
212 return (info);
213 }
214 return (NULL);
215 }
216
217 /*
218 * Handle the loading of a new module by populating a module_info for it. This
219 * is called for both preloaded and dynamically loaded modules.
220 */
221 void
unwind_module_loaded(struct linker_file * lf)222 unwind_module_loaded(struct linker_file *lf)
223 {
224 struct module_info *info;
225
226 /*
227 * A module that contains only data may have no unwind info; don't
228 * create any module info for it.
229 */
230 if (lf->exidx_size == 0)
231 return;
232
233 /*
234 * Find an unused entry in the existing list to reuse. If we don't find
235 * one, create a new one and link it into the list. This is the only
236 * place the module_list is modified. Adding a new entry to the list
237 * will not perturb any other threads currently walking the list. This
238 * function is invoked while kern_linker is still holding its lock
239 * to prevent its module list from being modified, so we don't have to
240 * worry about racing other threads doing an insert concurrently.
241 */
242 if ((info = find_module_info(0)) == NULL) {
243 info = create_module_info();
244 }
245 populate_module_info(info, lf);
246 }
247
248 /* Handle the unloading of a module. */
249 void
unwind_module_unloaded(struct linker_file * lf)250 unwind_module_unloaded(struct linker_file *lf)
251 {
252 struct module_info *info;
253
254 /*
255 * A module that contains only data may have no unwind info and there
256 * won't be a list entry for it.
257 */
258 if (lf->exidx_size == 0)
259 return;
260
261 /*
262 * When a module is unloaded, we clear the info out of its entry in the
263 * module list, making that entry available for later reuse.
264 */
265 if ((info = find_module_info(UADDR(lf->address))) == NULL) {
266 printf("arm unwind: module '%s' not on list at unload time\n",
267 lf->filename);
268 return;
269 }
270 clear_module_info(info);
271 }
272
273 /*
274 * Initialization must run fairly early, as soon as malloc(9) is available, and
275 * definitely before witness, which uses stack(9). We synthesize a module_info
276 * entry for the kernel, because unwind_module_loaded() doesn't get called for
277 * it. Also, it is unlike other modules in that the elf metadata for locating
278 * the unwind tables might be stripped, so instead we have to use the
279 * _exidx_start/end symbols created by ldscript.arm.
280 */
281 static void
module_info_init(void * arg __unused)282 module_info_init(void *arg __unused)
283 {
284 struct linker_file thekernel;
285
286 STAILQ_INIT(&module_list);
287
288 thekernel.filename = "kernel";
289 thekernel.address = CADDR(&_start);
290 thekernel.size = UADDR(&_end) - UADDR(&_start);
291 thekernel.exidx_addr = CADDR(&_exidx_start);
292 thekernel.exidx_size = UADDR(&_exidx_end) - UADDR(&_exidx_start);
293 populate_module_info(create_module_info(), &thekernel);
294 }
295 SYSINIT(unwind_init, SI_SUB_KMEM, SI_ORDER_ANY, module_info_init, NULL);
296
297 /* Expand a 31-bit signed value to a 32-bit signed value */
298 static __inline int32_t
expand_prel31(uint32_t prel31)299 expand_prel31(uint32_t prel31)
300 {
301
302 return ((int32_t)(prel31 & 0x7fffffffu) << 1) / 2;
303 }
304
305 /*
306 * Perform a binary search of the index table to find the function
307 * with the largest address that doesn't exceed addr.
308 */
309 static struct unwind_idx *
find_index(uint32_t addr)310 find_index(uint32_t addr)
311 {
312 struct module_info *info;
313 unsigned int min, mid, max;
314 struct unwind_idx *start;
315 struct unwind_idx *item;
316 int32_t prel31_addr;
317 uint32_t func_addr;
318
319 info = find_module_info(addr);
320 if (info == NULL)
321 return NULL;
322
323 min = 0;
324 max = (info->exidx_end - info->exidx_start) / sizeof(struct unwind_idx);
325 start = (struct unwind_idx *)CADDR(info->exidx_start);
326
327 while (min != max) {
328 mid = min + (max - min + 1) / 2;
329
330 item = &start[mid];
331
332 prel31_addr = expand_prel31(item->offset);
333 func_addr = (uint32_t)&item->offset + prel31_addr;
334
335 if (func_addr <= addr) {
336 min = mid;
337 } else {
338 max = mid - 1;
339 }
340 }
341
342 return &start[min];
343 }
344
345 /* Reads the next byte from the instruction list */
346 static uint8_t
unwind_exec_read_byte(struct unwind_state * state)347 unwind_exec_read_byte(struct unwind_state *state)
348 {
349 uint8_t insn;
350
351 /* Read the unwind instruction */
352 insn = (*state->insn) >> (state->byte * 8);
353
354 /* Update the location of the next instruction */
355 if (state->byte == 0) {
356 state->byte = 3;
357 state->insn++;
358 state->entries--;
359 } else
360 state->byte--;
361
362 return insn;
363 }
364
365 /* Executes the next instruction on the list */
366 static int
unwind_exec_insn(struct unwind_state * state)367 unwind_exec_insn(struct unwind_state *state)
368 {
369 struct thread *td = curthread;
370 unsigned int insn;
371 uint32_t *vsp = (uint32_t *)state->registers[SP];
372 int update_vsp = 0;
373
374 /* This should never happen */
375 if (state->entries == 0)
376 return 1;
377
378 /* Read the next instruction */
379 insn = unwind_exec_read_byte(state);
380
381 if ((insn & INSN_VSP_MASK) == INSN_VSP_INC) {
382 state->registers[SP] += ((insn & INSN_VSP_SIZE_MASK) << 2) + 4;
383
384 } else if ((insn & INSN_VSP_MASK) == INSN_VSP_DEC) {
385 state->registers[SP] -= ((insn & INSN_VSP_SIZE_MASK) << 2) + 4;
386
387 } else if ((insn & INSN_STD_MASK) == INSN_POP_MASKED) {
388 unsigned int mask, reg;
389
390 /* Load the mask */
391 mask = unwind_exec_read_byte(state);
392 mask |= (insn & INSN_STD_DATA_MASK) << 8;
393
394 /* We have a refuse to unwind instruction */
395 if (mask == 0)
396 return 1;
397
398 if (!__is_aligned(vsp, sizeof(register_t)))
399 return 1;
400
401 /* Update SP */
402 update_vsp = 1;
403
404 /* Load the registers */
405 for (reg = 4; mask && reg < 16; mask >>= 1, reg++) {
406 if (mask & 1) {
407 if (!kstack_contains(td, (uintptr_t)vsp,
408 sizeof(*vsp)))
409 return 1;
410
411 state->registers[reg] = *vsp++;
412 state->update_mask |= 1 << reg;
413
414 /* If we have updated SP kep its value */
415 if (reg == SP)
416 update_vsp = 0;
417 }
418 }
419
420 } else if ((insn & INSN_STD_MASK) == INSN_VSP_REG &&
421 ((insn & INSN_STD_DATA_MASK) != 13) &&
422 ((insn & INSN_STD_DATA_MASK) != 15)) {
423 /* sp = register */
424 state->registers[SP] =
425 state->registers[insn & INSN_STD_DATA_MASK];
426
427 } else if ((insn & INSN_STD_MASK) == INSN_POP_COUNT) {
428 unsigned int count, reg;
429
430 /* Read how many registers to load */
431 count = insn & INSN_POP_COUNT_MASK;
432
433 if (!__is_aligned(vsp, sizeof(register_t)))
434 return 1;
435
436 /* Update sp */
437 update_vsp = 1;
438
439 /* Pop the registers */
440 if (!kstack_contains(td, (uintptr_t)vsp,
441 sizeof(*vsp) * (4 + count)))
442 return 1;
443 for (reg = 4; reg <= 4 + count; reg++) {
444 state->registers[reg] = *vsp++;
445 state->update_mask |= 1 << reg;
446 }
447
448 /* Check if we are in the pop r14 version */
449 if ((insn & INSN_POP_TYPE_MASK) != 0) {
450 if (!kstack_contains(td, (uintptr_t)vsp, sizeof(*vsp)))
451 return 1;
452 state->registers[14] = *vsp++;
453 }
454
455 } else if (insn == INSN_FINISH) {
456 /* Stop processing */
457 state->entries = 0;
458
459 } else if (insn == INSN_POP_REGS) {
460 unsigned int mask, reg;
461
462 mask = unwind_exec_read_byte(state);
463 if (mask == 0 || (mask & 0xf0) != 0)
464 return 1;
465
466 if (!__is_aligned(vsp, sizeof(register_t)))
467 return 1;
468
469 /* Update SP */
470 update_vsp = 1;
471
472 /* Load the registers */
473 for (reg = 0; mask && reg < 4; mask >>= 1, reg++) {
474 if (mask & 1) {
475 if (!kstack_contains(td, (uintptr_t)vsp,
476 sizeof(*vsp)))
477 return 1;
478 state->registers[reg] = *vsp++;
479 state->update_mask |= 1 << reg;
480 }
481 }
482
483 } else if ((insn & INSN_VSP_LARGE_INC_MASK) == INSN_VSP_LARGE_INC) {
484 unsigned int uleb128;
485
486 /* Read the increment value */
487 uleb128 = unwind_exec_read_byte(state);
488
489 state->registers[SP] += 0x204 + (uleb128 << 2);
490
491 } else {
492 /* We hit a new instruction that needs to be implemented */
493 #if 0
494 db_printf("Unhandled instruction %.2x\n", insn);
495 #endif
496 return 1;
497 }
498
499 if (update_vsp) {
500 state->registers[SP] = (uint32_t)vsp;
501 }
502
503 #if 0
504 db_printf("fp = %08x, sp = %08x, lr = %08x, pc = %08x\n",
505 state->registers[FP], state->registers[SP], state->registers[LR],
506 state->registers[PC]);
507 #endif
508
509 return 0;
510 }
511
512 /* Performs the unwind of a function */
513 static int
unwind_tab(struct unwind_state * state)514 unwind_tab(struct unwind_state *state)
515 {
516 uint32_t entry;
517
518 /* Set PC to a known value */
519 state->registers[PC] = 0;
520
521 /* Read the personality */
522 entry = *state->insn & ENTRY_MASK;
523
524 if (entry == ENTRY_ARM_SU16) {
525 state->byte = 2;
526 state->entries = 1;
527 } else if (entry == ENTRY_ARM_LU16) {
528 state->byte = 1;
529 state->entries = ((*state->insn >> 16) & 0xFF) + 1;
530 } else {
531 #if 0
532 db_printf("Unknown entry: %x\n", entry);
533 #endif
534 return 1;
535 }
536
537 while (state->entries > 0) {
538 if (unwind_exec_insn(state) != 0)
539 return 1;
540 }
541
542 /*
543 * The program counter was not updated, load it from the link register.
544 */
545 if (state->registers[PC] == 0) {
546 state->registers[PC] = state->registers[LR];
547
548 /*
549 * If the program counter changed, flag it in the update mask.
550 */
551 if (state->start_pc != state->registers[PC])
552 state->update_mask |= 1 << PC;
553 }
554
555 return 0;
556 }
557
558 /*
559 * Unwind a single stack frame.
560 * Return 0 on success or 1 if the stack cannot be unwound any further.
561 *
562 * XXX The can_lock argument is no longer germane; a sweep of callers should be
563 * made to remove it after this new code has proven itself for a while.
564 */
565 int
unwind_stack_one(struct unwind_state * state,int can_lock __unused)566 unwind_stack_one(struct unwind_state *state, int can_lock __unused)
567 {
568 struct unwind_idx *index;
569
570 /* Reset the mask of updated registers */
571 state->update_mask = 0;
572
573 /* The pc value is correct and will be overwritten, save it */
574 state->start_pc = state->registers[PC];
575
576 /* Find the item to run */
577 index = find_index(state->start_pc);
578 if (index == NULL || index->insn == EXIDX_CANTUNWIND)
579 return 1;
580
581 if (index->insn & (1U << 31)) {
582 /* The data is within the instruction */
583 state->insn = &index->insn;
584 } else {
585 /* A prel31 offset to the unwind table */
586 state->insn = (uint32_t *)
587 ((uintptr_t)&index->insn +
588 expand_prel31(index->insn));
589 }
590
591 /* Run the unwind function, return its finished/not-finished status. */
592 return (unwind_tab(state));
593 }
594