1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/export.h>
3 #include <linux/kprobes.h>
4 #include <linux/sched.h>
5 #include <linux/sched/debug.h>
6 #include <linux/stacktrace.h>
7
8 #include <asm/sections.h>
9 #include <asm/stacktrace.h>
10 #include <asm/traps.h>
11
12 #include "reboot.h"
13
14 #if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
15 /*
16 * Unwind the current stack frame and store the new register values in the
17 * structure passed as argument. Unwinding is equivalent to a function return,
18 * hence the new PC value rather than LR should be used for backtrace.
19 *
20 * With framepointer enabled, a simple function prologue looks like this:
21 * mov ip, sp
22 * stmdb sp!, {fp, ip, lr, pc}
23 * sub fp, ip, #4
24 *
25 * A simple function epilogue looks like this:
26 * ldm sp, {fp, sp, pc}
27 *
28 * When compiled with clang, pc and sp are not pushed. A simple function
29 * prologue looks like this when built with clang:
30 *
31 * stmdb {..., fp, lr}
32 * add fp, sp, #x
33 * sub sp, sp, #y
34 *
35 * A simple function epilogue looks like this when built with clang:
36 *
37 * sub sp, fp, #x
38 * ldm {..., fp, pc}
39 *
40 *
41 * Note that with framepointer enabled, even the leaf functions have the same
42 * prologue and epilogue, therefore we can ignore the LR value in this case.
43 */
44
45 extern unsigned long call_with_stack_end;
46
47 static int frame_pointer_check(struct stackframe *frame)
48 {
49 unsigned long high, low;
50 unsigned long fp = frame->fp;
51 unsigned long pc = frame->pc;
52
53 /*
54 * call_with_stack() is the only place we allow SP to jump from one
55 * stack to another, with FP and SP pointing to different stacks,
56 * skipping the FP boundary check at this point.
57 */
58 if (pc >= (unsigned long)&call_with_stack &&
59 pc < (unsigned long)&call_with_stack_end)
60 return 0;
61
62 /* only go to a higher address on the stack */
63 low = frame->sp;
64 high = ALIGN(low, THREAD_SIZE);
65
66 /* check current frame pointer is within bounds */
67 #ifdef CONFIG_CC_IS_CLANG
68 if (fp < low + 4 || fp > high - 4)
69 return -EINVAL;
70 #else
71 if (fp < low + 12 || fp > high - 4)
72 return -EINVAL;
73 #endif
74
75 return 0;
76 }
77
78 int notrace unwind_frame(struct stackframe *frame)
79 {
80 unsigned long fp = frame->fp;
81
82 if (frame_pointer_check(frame))
83 return -EINVAL;
84
85 /*
86 * When we unwind through an exception stack, include the saved PC
87 * value into the stack trace.
88 */
89 if (frame->ex_frame) {
90 struct pt_regs *regs = (struct pt_regs *)frame->sp;
91
92 /*
93 * We check that 'regs + sizeof(struct pt_regs)' (that is,
94 * ®s[1]) does not exceed the bottom of the stack to avoid
95 * accessing data outside the task's stack. This may happen
96 * when frame->ex_frame is a false positive.
97 */
98 if ((unsigned long)®s[1] > ALIGN(frame->sp, THREAD_SIZE))
99 return -EINVAL;
100
101 frame->pc = regs->ARM_pc;
102 frame->ex_frame = false;
103 return 0;
104 }
105
106 /* restore the registers from the stack frame */
107 #ifdef CONFIG_CC_IS_CLANG
108 frame->sp = frame->fp;
109 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
110 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 4));
111 #else
112 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 12));
113 frame->sp = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 8));
114 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 4));
115 #endif
116 #ifdef CONFIG_KRETPROBES
117 if (is_kretprobe_trampoline(frame->pc))
118 frame->pc = kretprobe_find_ret_addr(frame->tsk,
119 (void *)frame->fp, &frame->kr_cur);
120 #endif
121
122 if (in_entry_text(frame->pc))
123 frame->ex_frame = true;
124
125 return 0;
126 }
127 #endif
128
129 void notrace walk_stackframe(struct stackframe *frame,
130 bool (*fn)(void *, unsigned long), void *data)
131 {
132 while (1) {
133 int ret;
134
135 if (!fn(data, frame->pc))
136 break;
137 ret = unwind_frame(frame);
138 if (ret < 0)
139 break;
140 }
141 }
142 EXPORT_SYMBOL(walk_stackframe);
143
144 #ifdef CONFIG_STACKTRACE
145 static void start_stack_trace(struct stackframe *frame, struct task_struct *task,
146 unsigned long fp, unsigned long sp,
147 unsigned long lr, unsigned long pc)
148 {
149 frame->fp = fp;
150 frame->sp = sp;
151 frame->lr = lr;
152 frame->pc = pc;
153 #ifdef CONFIG_KRETPROBES
154 frame->kr_cur = NULL;
155 frame->tsk = task;
156 #endif
157 #ifdef CONFIG_UNWINDER_FRAME_POINTER
158 frame->ex_frame = in_entry_text(frame->pc);
159 #endif
160 }
161
162 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
163 struct task_struct *task, struct pt_regs *regs)
164 {
165 struct stackframe frame;
166
167 if (regs) {
168 start_stack_trace(&frame, NULL, regs->ARM_fp, regs->ARM_sp,
169 regs->ARM_lr, regs->ARM_pc);
170 } else if (task != current) {
171 #ifdef CONFIG_SMP
172 /*
173 * What guarantees do we have here that 'tsk' is not
174 * running on another CPU? For now, ignore it as we
175 * can't guarantee we won't explode.
176 */
177 return;
178 #else
179 start_stack_trace(&frame, task, thread_saved_fp(task),
180 thread_saved_sp(task), 0,
181 thread_saved_pc(task));
182 #endif
183 } else {
184 here:
185 start_stack_trace(&frame, task,
186 (unsigned long)__builtin_frame_address(0),
187 current_stack_pointer,
188 (unsigned long)__builtin_return_address(0),
189 (unsigned long)&&here);
190 /* skip this function */
191 if (unwind_frame(&frame))
192 return;
193 }
194
195 walk_stackframe(&frame, consume_entry, cookie);
196 }
197 #endif
198
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