xref: /linux/arch/arm64/kernel/stacktrace.c (revision c88fb897c1fb5a590dc6353ac4b01c8f46a347b3)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Stack tracing support
4  *
5  * Copyright (C) 2012 ARM Ltd.
6  */
7 #include <linux/kernel.h>
8 #include <linux/export.h>
9 #include <linux/ftrace.h>
10 #include <linux/kprobes.h>
11 #include <linux/sched.h>
12 #include <linux/sched/debug.h>
13 #include <linux/sched/task_stack.h>
14 #include <linux/stacktrace.h>
15 
16 #include <asm/irq.h>
17 #include <asm/pointer_auth.h>
18 #include <asm/stack_pointer.h>
19 #include <asm/stacktrace.h>
20 
21 /*
22  * AArch64 PCS assigns the frame pointer to x29.
23  *
24  * A simple function prologue looks like this:
25  * 	sub	sp, sp, #0x10
26  *   	stp	x29, x30, [sp]
27  *	mov	x29, sp
28  *
29  * A simple function epilogue looks like this:
30  *	mov	sp, x29
31  *	ldp	x29, x30, [sp]
32  *	add	sp, sp, #0x10
33  */
34 
35 /*
36  * Unwind from one frame record (A) to the next frame record (B).
37  *
38  * We terminate early if the location of B indicates a malformed chain of frame
39  * records (e.g. a cycle), determined based on the location and fp value of A
40  * and the location (but not the fp value) of B.
41  */
42 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
43 {
44 	unsigned long fp = frame->fp;
45 	struct stack_info info;
46 
47 	/* Terminal record; nothing to unwind */
48 	if (!fp)
49 		return -EINVAL;
50 
51 	if (fp & 0xf)
52 		return -EINVAL;
53 
54 	if (!tsk)
55 		tsk = current;
56 
57 	if (!on_accessible_stack(tsk, fp, &info))
58 		return -EINVAL;
59 
60 	if (test_bit(info.type, frame->stacks_done))
61 		return -EINVAL;
62 
63 	/*
64 	 * As stacks grow downward, any valid record on the same stack must be
65 	 * at a strictly higher address than the prior record.
66 	 *
67 	 * Stacks can nest in several valid orders, e.g.
68 	 *
69 	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
70 	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
71 	 *
72 	 * ... but the nesting itself is strict. Once we transition from one
73 	 * stack to another, it's never valid to unwind back to that first
74 	 * stack.
75 	 */
76 	if (info.type == frame->prev_type) {
77 		if (fp <= frame->prev_fp)
78 			return -EINVAL;
79 	} else {
80 		set_bit(frame->prev_type, frame->stacks_done);
81 	}
82 
83 	/*
84 	 * Record this frame record's values and location. The prev_fp and
85 	 * prev_type are only meaningful to the next unwind_frame() invocation.
86 	 */
87 	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
88 	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
89 	frame->prev_fp = fp;
90 	frame->prev_type = info.type;
91 
92 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
93 	if (tsk->ret_stack &&
94 		(ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
95 		struct ftrace_ret_stack *ret_stack;
96 		/*
97 		 * This is a case where function graph tracer has
98 		 * modified a return address (LR) in a stack frame
99 		 * to hook a function return.
100 		 * So replace it to an original value.
101 		 */
102 		ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
103 		if (WARN_ON_ONCE(!ret_stack))
104 			return -EINVAL;
105 		frame->pc = ret_stack->ret;
106 	}
107 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
108 
109 	frame->pc = ptrauth_strip_insn_pac(frame->pc);
110 
111 	return 0;
112 }
113 NOKPROBE_SYMBOL(unwind_frame);
114 
115 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
116 			     bool (*fn)(void *, unsigned long), void *data)
117 {
118 	while (1) {
119 		int ret;
120 
121 		if (!fn(data, frame->pc))
122 			break;
123 		ret = unwind_frame(tsk, frame);
124 		if (ret < 0)
125 			break;
126 	}
127 }
128 NOKPROBE_SYMBOL(walk_stackframe);
129 
130 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
131 {
132 	printk("%s %pS\n", loglvl, (void *)where);
133 }
134 
135 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
136 		    const char *loglvl)
137 {
138 	struct stackframe frame;
139 	int skip = 0;
140 
141 	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
142 
143 	if (regs) {
144 		if (user_mode(regs))
145 			return;
146 		skip = 1;
147 	}
148 
149 	if (!tsk)
150 		tsk = current;
151 
152 	if (!try_get_task_stack(tsk))
153 		return;
154 
155 	if (tsk == current) {
156 		start_backtrace(&frame,
157 				(unsigned long)__builtin_frame_address(0),
158 				(unsigned long)dump_backtrace);
159 	} else {
160 		/*
161 		 * task blocked in __switch_to
162 		 */
163 		start_backtrace(&frame,
164 				thread_saved_fp(tsk),
165 				thread_saved_pc(tsk));
166 	}
167 
168 	printk("%sCall trace:\n", loglvl);
169 	do {
170 		/* skip until specified stack frame */
171 		if (!skip) {
172 			dump_backtrace_entry(frame.pc, loglvl);
173 		} else if (frame.fp == regs->regs[29]) {
174 			skip = 0;
175 			/*
176 			 * Mostly, this is the case where this function is
177 			 * called in panic/abort. As exception handler's
178 			 * stack frame does not contain the corresponding pc
179 			 * at which an exception has taken place, use regs->pc
180 			 * instead.
181 			 */
182 			dump_backtrace_entry(regs->pc, loglvl);
183 		}
184 	} while (!unwind_frame(tsk, &frame));
185 
186 	put_task_stack(tsk);
187 }
188 
189 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
190 {
191 	dump_backtrace(NULL, tsk, loglvl);
192 	barrier();
193 }
194 
195 #ifdef CONFIG_STACKTRACE
196 
197 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
198 		     struct task_struct *task, struct pt_regs *regs)
199 {
200 	struct stackframe frame;
201 
202 	if (regs)
203 		start_backtrace(&frame, regs->regs[29], regs->pc);
204 	else if (task == current)
205 		start_backtrace(&frame,
206 				(unsigned long)__builtin_frame_address(0),
207 				(unsigned long)arch_stack_walk);
208 	else
209 		start_backtrace(&frame, thread_saved_fp(task),
210 				thread_saved_pc(task));
211 
212 	walk_stackframe(task, &frame, consume_entry, cookie);
213 }
214 
215 #endif
216