summaryrefslogtreecommitdiffstats
path: root/arch/arm64/kernel/stacktrace.c
blob: fa56af1a59c39fd452bd31ec29486067430724e3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Stack tracing support
 *
 * Copyright (C) 2012 ARM Ltd.
 */
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>

#include <asm/irq.h>
#include <asm/pointer_auth.h>
#include <asm/stack_pointer.h>
#include <asm/stacktrace.h>

/*
 * AArch64 PCS assigns the frame pointer to x29.
 *
 * A simple function prologue looks like this:
 * 	sub	sp, sp, #0x10
 *   	stp	x29, x30, [sp]
 *	mov	x29, sp
 *
 * A simple function epilogue looks like this:
 *	mov	sp, x29
 *	ldp	x29, x30, [sp]
 *	add	sp, sp, #0x10
 */

/*
 * Unwind from one frame record (A) to the next frame record (B).
 *
 * We terminate early if the location of B indicates a malformed chain of frame
 * records (e.g. a cycle), determined based on the location and fp value of A
 * and the location (but not the fp value) of B.
 */
int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
{
	unsigned long fp = frame->fp;
	struct stack_info info;

	if (fp & 0xf)
		return -EINVAL;

	if (!tsk)
		tsk = current;

	if (!on_accessible_stack(tsk, fp, &info))
		return -EINVAL;

	if (test_bit(info.type, frame->stacks_done))
		return -EINVAL;

	/*
	 * As stacks grow downward, any valid record on the same stack must be
	 * at a strictly higher address than the prior record.
	 *
	 * Stacks can nest in several valid orders, e.g.
	 *
	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
	 *
	 * ... but the nesting itself is strict. Once we transition from one
	 * stack to another, it's never valid to unwind back to that first
	 * stack.
	 */
	if (info.type == frame->prev_type) {
		if (fp <= frame->prev_fp)
			return -EINVAL;
	} else {
		set_bit(frame->prev_type, frame->stacks_done);
	}

	/*
	 * Record this frame record's values and location. The prev_fp and
	 * prev_type are only meaningful to the next unwind_frame() invocation.
	 */
	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
	frame->prev_fp = fp;
	frame->prev_type = info.type;

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	if (tsk->ret_stack &&
		(ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
		struct ftrace_ret_stack *ret_stack;
		/*
		 * This is a case where function graph tracer has
		 * modified a return address (LR) in a stack frame
		 * to hook a function return.
		 * So replace it to an original value.
		 */
		ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
		if (WARN_ON_ONCE(!ret_stack))
			return -EINVAL;
		frame->pc = ret_stack->ret;
	}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

	frame->pc = ptrauth_strip_insn_pac(frame->pc);

	/*
	 * Frames created upon entry from EL0 have NULL FP and PC values, so
	 * don't bother reporting these. Frames created by __noreturn functions
	 * might have a valid FP even if PC is bogus, so only terminate where
	 * both are NULL.
	 */
	if (!frame->fp && !frame->pc)
		return -EINVAL;

	return 0;
}
NOKPROBE_SYMBOL(unwind_frame);

void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
			     bool (*fn)(void *, unsigned long), void *data)
{
	while (1) {
		int ret;

		if (!fn(data, frame->pc))
			break;
		ret = unwind_frame(tsk, frame);
		if (ret < 0)
			break;
	}
}
NOKPROBE_SYMBOL(walk_stackframe);

static void dump_backtrace_entry(unsigned long where, const char *loglvl)
{
	printk("%s %pS\n", loglvl, (void *)where);
}

void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
		    const char *loglvl)
{
	struct stackframe frame;
	int skip = 0;

	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

	if (regs) {
		if (user_mode(regs))
			return;
		skip = 1;
	}

	if (!tsk)
		tsk = current;

	if (!try_get_task_stack(tsk))
		return;

	if (tsk == current) {
		start_backtrace(&frame,
				(unsigned long)__builtin_frame_address(0),
				(unsigned long)dump_backtrace);
	} else {
		/*
		 * task blocked in __switch_to
		 */
		start_backtrace(&frame,
				thread_saved_fp(tsk),
				thread_saved_pc(tsk));
	}

	printk("%sCall trace:\n", loglvl);
	do {
		/* skip until specified stack frame */
		if (!skip) {
			dump_backtrace_entry(frame.pc, loglvl);
		} else if (frame.fp == regs->regs[29]) {
			skip = 0;
			/*
			 * Mostly, this is the case where this function is
			 * called in panic/abort. As exception handler's
			 * stack frame does not contain the corresponding pc
			 * at which an exception has taken place, use regs->pc
			 * instead.
			 */
			dump_backtrace_entry(regs->pc, loglvl);
		}
	} while (!unwind_frame(tsk, &frame));

	put_task_stack(tsk);
}

void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
{
	dump_backtrace(NULL, tsk, loglvl);
	barrier();
}

#ifdef CONFIG_STACKTRACE

void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
		     struct task_struct *task, struct pt_regs *regs)
{
	struct stackframe frame;

	if (regs)
		start_backtrace(&frame, regs->regs[29], regs->pc);
	else if (task == current)
		start_backtrace(&frame,
				(unsigned long)__builtin_frame_address(0),
				(unsigned long)arch_stack_walk);
	else
		start_backtrace(&frame, thread_saved_fp(task),
				thread_saved_pc(task));

	walk_stackframe(task, &frame, consume_entry, cookie);
}

#endif