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 */
40void __aeabi_unwind_cpp_pr0(void)
41{
42};
43EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);
44
45void __aeabi_unwind_cpp_pr1(void)
46{
47};
48EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);
49
50void __aeabi_unwind_cpp_pr2(void)
51{
52};
53EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
54
55struct 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
69enum 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
80extern const struct unwind_idx __start_unwind_idx[];
81static const struct unwind_idx *__origin_unwind_idx;
82extern const struct unwind_idx __stop_unwind_idx[];
83
84static DEFINE_RAW_SPINLOCK(unwind_lock);
85static 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 */
103static 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
153static 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
171static 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
211static 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 */
233static 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 */
251static 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
272static 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
292static 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
311static 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 */
337static 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
398error:
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 */
406int 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
522void 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		 */
547here:
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
572struct 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
598void 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}
611