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/stack_pointer.h> 18 #include <asm/stacktrace.h> 19 20 /* 21 * AArch64 PCS assigns the frame pointer to x29. 22 * 23 * A simple function prologue looks like this: 24 * sub sp, sp, #0x10 25 * stp x29, x30, [sp] 26 * mov x29, sp 27 * 28 * A simple function epilogue looks like this: 29 * mov sp, x29 30 * ldp x29, x30, [sp] 31 * add sp, sp, #0x10 32 */ 33 34 /* 35 * Unwind from one frame record (A) to the next frame record (B). 36 * 37 * We terminate early if the location of B indicates a malformed chain of frame 38 * records (e.g. a cycle), determined based on the location and fp value of A 39 * and the location (but not the fp value) of B. 40 */ 41 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) 42 { 43 unsigned long fp = frame->fp; 44 struct stack_info info; 45 46 if (fp & 0xf) 47 return -EINVAL; 48 49 if (!tsk) 50 tsk = current; 51 52 if (!on_accessible_stack(tsk, fp, &info)) 53 return -EINVAL; 54 55 if (test_bit(info.type, frame->stacks_done)) 56 return -EINVAL; 57 58 /* 59 * As stacks grow downward, any valid record on the same stack must be 60 * at a strictly higher address than the prior record. 61 * 62 * Stacks can nest in several valid orders, e.g. 63 * 64 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 65 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 66 * 67 * ... but the nesting itself is strict. Once we transition from one 68 * stack to another, it's never valid to unwind back to that first 69 * stack. 70 */ 71 if (info.type == frame->prev_type) { 72 if (fp <= frame->prev_fp) 73 return -EINVAL; 74 } else { 75 set_bit(frame->prev_type, frame->stacks_done); 76 } 77 78 /* 79 * Record this frame record's values and location. The prev_fp and 80 * prev_type are only meaningful to the next unwind_frame() invocation. 81 */ 82 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 83 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 84 frame->prev_fp = fp; 85 frame->prev_type = info.type; 86 87 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 88 if (tsk->ret_stack && 89 (frame->pc == (unsigned long)return_to_handler)) { 90 struct ftrace_ret_stack *ret_stack; 91 /* 92 * This is a case where function graph tracer has 93 * modified a return address (LR) in a stack frame 94 * to hook a function return. 95 * So replace it to an original value. 96 */ 97 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++); 98 if (WARN_ON_ONCE(!ret_stack)) 99 return -EINVAL; 100 frame->pc = ret_stack->ret; 101 } 102 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 103 104 /* 105 * Frames created upon entry from EL0 have NULL FP and PC values, so 106 * don't bother reporting these. Frames created by __noreturn functions 107 * might have a valid FP even if PC is bogus, so only terminate where 108 * both are NULL. 109 */ 110 if (!frame->fp && !frame->pc) 111 return -EINVAL; 112 113 return 0; 114 } 115 NOKPROBE_SYMBOL(unwind_frame); 116 117 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame, 118 int (*fn)(struct stackframe *, void *), void *data) 119 { 120 while (1) { 121 int ret; 122 123 if (fn(frame, data)) 124 break; 125 ret = unwind_frame(tsk, frame); 126 if (ret < 0) 127 break; 128 } 129 } 130 NOKPROBE_SYMBOL(walk_stackframe); 131 132 #ifdef CONFIG_STACKTRACE 133 struct stack_trace_data { 134 struct stack_trace *trace; 135 unsigned int no_sched_functions; 136 unsigned int skip; 137 }; 138 139 static int save_trace(struct stackframe *frame, void *d) 140 { 141 struct stack_trace_data *data = d; 142 struct stack_trace *trace = data->trace; 143 unsigned long addr = frame->pc; 144 145 if (data->no_sched_functions && in_sched_functions(addr)) 146 return 0; 147 if (data->skip) { 148 data->skip--; 149 return 0; 150 } 151 152 trace->entries[trace->nr_entries++] = addr; 153 154 return trace->nr_entries >= trace->max_entries; 155 } 156 157 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace) 158 { 159 struct stack_trace_data data; 160 struct stackframe frame; 161 162 data.trace = trace; 163 data.skip = trace->skip; 164 data.no_sched_functions = 0; 165 166 start_backtrace(&frame, regs->regs[29], regs->pc); 167 walk_stackframe(current, &frame, save_trace, &data); 168 } 169 EXPORT_SYMBOL_GPL(save_stack_trace_regs); 170 171 static noinline void __save_stack_trace(struct task_struct *tsk, 172 struct stack_trace *trace, unsigned int nosched) 173 { 174 struct stack_trace_data data; 175 struct stackframe frame; 176 177 if (!try_get_task_stack(tsk)) 178 return; 179 180 data.trace = trace; 181 data.skip = trace->skip; 182 data.no_sched_functions = nosched; 183 184 if (tsk != current) { 185 start_backtrace(&frame, thread_saved_fp(tsk), 186 thread_saved_pc(tsk)); 187 } else { 188 /* We don't want this function nor the caller */ 189 data.skip += 2; 190 start_backtrace(&frame, 191 (unsigned long)__builtin_frame_address(0), 192 (unsigned long)__save_stack_trace); 193 } 194 195 walk_stackframe(tsk, &frame, save_trace, &data); 196 197 put_task_stack(tsk); 198 } 199 EXPORT_SYMBOL_GPL(save_stack_trace_tsk); 200 201 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace) 202 { 203 __save_stack_trace(tsk, trace, 1); 204 } 205 206 void save_stack_trace(struct stack_trace *trace) 207 { 208 __save_stack_trace(current, trace, 0); 209 } 210 211 EXPORT_SYMBOL_GPL(save_stack_trace); 212 #endif 213