xref: /openbmc/linux/arch/arm/kernel/unwind.c (revision 0cb4228f)
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 /*
312  * Execute the current unwind instruction.
313  */
314 static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
315 {
316 	unsigned long insn = unwind_get_byte(ctrl);
317 	int ret = URC_OK;
318 
319 	pr_debug("%s: insn = %08lx\n", __func__, insn);
320 
321 	if ((insn & 0xc0) == 0x00)
322 		ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
323 	else if ((insn & 0xc0) == 0x40) {
324 		ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
325 	} else if ((insn & 0xf0) == 0x80) {
326 		unsigned long mask;
327 
328 		insn = (insn << 8) | unwind_get_byte(ctrl);
329 		mask = insn & 0x0fff;
330 		if (mask == 0) {
331 			pr_warn("unwind: 'Refuse to unwind' instruction %04lx\n",
332 				insn);
333 			return -URC_FAILURE;
334 		}
335 
336 		ret = unwind_exec_pop_subset_r4_to_r13(ctrl, mask);
337 		if (ret)
338 			goto error;
339 	} else if ((insn & 0xf0) == 0x90 &&
340 		   (insn & 0x0d) != 0x0d) {
341 		ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
342 	} else if ((insn & 0xf0) == 0xa0) {
343 		ret = unwind_exec_pop_r4_to_rN(ctrl, insn);
344 		if (ret)
345 			goto error;
346 	} else if (insn == 0xb0) {
347 		if (ctrl->vrs[PC] == 0)
348 			ctrl->vrs[PC] = ctrl->vrs[LR];
349 		/* no further processing */
350 		ctrl->entries = 0;
351 	} else if (insn == 0xb1) {
352 		unsigned long mask = unwind_get_byte(ctrl);
353 
354 		if (mask == 0 || mask & 0xf0) {
355 			pr_warn("unwind: Spare encoding %04lx\n",
356 				(insn << 8) | mask);
357 			return -URC_FAILURE;
358 		}
359 
360 		ret = unwind_exec_pop_subset_r0_to_r3(ctrl, mask);
361 		if (ret)
362 			goto error;
363 	} else if (insn == 0xb2) {
364 		unsigned long uleb128 = unwind_get_byte(ctrl);
365 
366 		ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
367 	} else {
368 		pr_warn("unwind: Unhandled instruction %02lx\n", insn);
369 		return -URC_FAILURE;
370 	}
371 
372 	pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
373 		 ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);
374 
375 error:
376 	return ret;
377 }
378 
379 /*
380  * Unwind a single frame starting with *sp for the symbol at *pc. It
381  * updates the *pc and *sp with the new values.
382  */
383 int unwind_frame(struct stackframe *frame)
384 {
385 	const struct unwind_idx *idx;
386 	struct unwind_ctrl_block ctrl;
387 	unsigned long sp_low;
388 
389 	/* store the highest address on the stack to avoid crossing it*/
390 	sp_low = frame->sp;
391 	ctrl.sp_high = ALIGN(sp_low - THREAD_SIZE, THREAD_ALIGN)
392 		       + THREAD_SIZE;
393 
394 	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
395 		 frame->pc, frame->lr, frame->sp);
396 
397 	idx = unwind_find_idx(frame->pc);
398 	if (!idx) {
399 		if (frame->pc && kernel_text_address(frame->pc)) {
400 			if (in_module_plt(frame->pc) && frame->pc != frame->lr) {
401 				/*
402 				 * Quoting Ard: Veneers only set PC using a
403 				 * PC+immediate LDR, and so they don't affect
404 				 * the state of the stack or the register file
405 				 */
406 				frame->pc = frame->lr;
407 				return URC_OK;
408 			}
409 			pr_warn("unwind: Index not found %08lx\n", frame->pc);
410 		}
411 		return -URC_FAILURE;
412 	}
413 
414 	ctrl.vrs[FP] = frame->fp;
415 	ctrl.vrs[SP] = frame->sp;
416 	ctrl.vrs[LR] = frame->lr;
417 	ctrl.vrs[PC] = 0;
418 
419 	if (idx->insn == 1)
420 		/* can't unwind */
421 		return -URC_FAILURE;
422 	else if (frame->pc == prel31_to_addr(&idx->addr_offset)) {
423 		/*
424 		 * Unwinding is tricky when we're halfway through the prologue,
425 		 * since the stack frame that the unwinder expects may not be
426 		 * fully set up yet. However, one thing we do know for sure is
427 		 * that if we are unwinding from the very first instruction of
428 		 * a function, we are still effectively in the stack frame of
429 		 * the caller, and the unwind info has no relevance yet.
430 		 */
431 		if (frame->pc == frame->lr)
432 			return -URC_FAILURE;
433 		frame->pc = frame->lr;
434 		return URC_OK;
435 	} else if ((idx->insn & 0x80000000) == 0)
436 		/* prel31 to the unwind table */
437 		ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
438 	else if ((idx->insn & 0xff000000) == 0x80000000)
439 		/* only personality routine 0 supported in the index */
440 		ctrl.insn = &idx->insn;
441 	else {
442 		pr_warn("unwind: Unsupported personality routine %08lx in the index at %p\n",
443 			idx->insn, idx);
444 		return -URC_FAILURE;
445 	}
446 
447 	/* check the personality routine */
448 	if ((*ctrl.insn & 0xff000000) == 0x80000000) {
449 		ctrl.byte = 2;
450 		ctrl.entries = 1;
451 	} else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
452 		ctrl.byte = 1;
453 		ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
454 	} else {
455 		pr_warn("unwind: Unsupported personality routine %08lx at %p\n",
456 			*ctrl.insn, ctrl.insn);
457 		return -URC_FAILURE;
458 	}
459 
460 	ctrl.check_each_pop = 0;
461 
462 	if (prel31_to_addr(&idx->addr_offset) == (u32)&call_with_stack) {
463 		/*
464 		 * call_with_stack() is the only place where we permit SP to
465 		 * jump from one stack to another, and since we know it is
466 		 * guaranteed to happen, set up the SP bounds accordingly.
467 		 */
468 		sp_low = frame->fp;
469 		ctrl.sp_high = ALIGN(frame->fp, THREAD_SIZE);
470 	}
471 
472 	while (ctrl.entries > 0) {
473 		int urc;
474 		if ((ctrl.sp_high - ctrl.vrs[SP]) < sizeof(ctrl.vrs))
475 			ctrl.check_each_pop = 1;
476 		urc = unwind_exec_insn(&ctrl);
477 		if (urc < 0)
478 			return urc;
479 		if (ctrl.vrs[SP] < sp_low || ctrl.vrs[SP] > ctrl.sp_high)
480 			return -URC_FAILURE;
481 	}
482 
483 	if (ctrl.vrs[PC] == 0)
484 		ctrl.vrs[PC] = ctrl.vrs[LR];
485 
486 	/* check for infinite loop */
487 	if (frame->pc == ctrl.vrs[PC] && frame->sp == ctrl.vrs[SP])
488 		return -URC_FAILURE;
489 
490 	frame->fp = ctrl.vrs[FP];
491 	frame->sp = ctrl.vrs[SP];
492 	frame->lr = ctrl.vrs[LR];
493 	frame->pc = ctrl.vrs[PC];
494 	frame->lr_addr = ctrl.lr_addr;
495 
496 	return URC_OK;
497 }
498 
499 void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk,
500 		      const char *loglvl)
501 {
502 	struct stackframe frame;
503 
504 	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
505 
506 	if (!tsk)
507 		tsk = current;
508 
509 	if (regs) {
510 		arm_get_current_stackframe(regs, &frame);
511 		/* PC might be corrupted, use LR in that case. */
512 		if (!kernel_text_address(regs->ARM_pc))
513 			frame.pc = regs->ARM_lr;
514 	} else if (tsk == current) {
515 		frame.fp = (unsigned long)__builtin_frame_address(0);
516 		frame.sp = current_stack_pointer;
517 		frame.lr = (unsigned long)__builtin_return_address(0);
518 		/* We are saving the stack and execution state at this
519 		 * point, so we should ensure that frame.pc is within
520 		 * this block of code.
521 		 */
522 here:
523 		frame.pc = (unsigned long)&&here;
524 	} else {
525 		/* task blocked in __switch_to */
526 		frame.fp = thread_saved_fp(tsk);
527 		frame.sp = thread_saved_sp(tsk);
528 		/*
529 		 * The function calling __switch_to cannot be a leaf function
530 		 * so LR is recovered from the stack.
531 		 */
532 		frame.lr = 0;
533 		frame.pc = thread_saved_pc(tsk);
534 	}
535 
536 	while (1) {
537 		int urc;
538 		unsigned long where = frame.pc;
539 
540 		urc = unwind_frame(&frame);
541 		if (urc < 0)
542 			break;
543 		dump_backtrace_entry(where, frame.pc, frame.sp - 4, loglvl);
544 	}
545 }
546 
547 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
548 				      unsigned long text_addr,
549 				      unsigned long text_size)
550 {
551 	unsigned long flags;
552 	struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
553 
554 	pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
555 		 text_addr, text_size);
556 
557 	if (!tab)
558 		return tab;
559 
560 	tab->start = (const struct unwind_idx *)start;
561 	tab->stop = (const struct unwind_idx *)(start + size);
562 	tab->origin = unwind_find_origin(tab->start, tab->stop);
563 	tab->begin_addr = text_addr;
564 	tab->end_addr = text_addr + text_size;
565 
566 	raw_spin_lock_irqsave(&unwind_lock, flags);
567 	list_add_tail(&tab->list, &unwind_tables);
568 	raw_spin_unlock_irqrestore(&unwind_lock, flags);
569 
570 	return tab;
571 }
572 
573 void unwind_table_del(struct unwind_table *tab)
574 {
575 	unsigned long flags;
576 
577 	if (!tab)
578 		return;
579 
580 	raw_spin_lock_irqsave(&unwind_lock, flags);
581 	list_del(&tab->list);
582 	raw_spin_unlock_irqrestore(&unwind_lock, flags);
583 
584 	kfree(tab);
585 }
586