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 if (fp & 0xf) 48 return -EINVAL; 49 50 if (!tsk) 51 tsk = current; 52 53 if (!on_accessible_stack(tsk, fp, &info)) 54 return -EINVAL; 55 56 if (test_bit(info.type, frame->stacks_done)) 57 return -EINVAL; 58 59 /* 60 * As stacks grow downward, any valid record on the same stack must be 61 * at a strictly higher address than the prior record. 62 * 63 * Stacks can nest in several valid orders, e.g. 64 * 65 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 66 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 67 * 68 * ... but the nesting itself is strict. Once we transition from one 69 * stack to another, it's never valid to unwind back to that first 70 * stack. 71 */ 72 if (info.type == frame->prev_type) { 73 if (fp <= frame->prev_fp) 74 return -EINVAL; 75 } else { 76 set_bit(frame->prev_type, frame->stacks_done); 77 } 78 79 /* 80 * Record this frame record's values and location. The prev_fp and 81 * prev_type are only meaningful to the next unwind_frame() invocation. 82 */ 83 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 84 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 85 frame->prev_fp = fp; 86 frame->prev_type = info.type; 87 88 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 89 if (tsk->ret_stack && 90 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) { 91 struct ftrace_ret_stack *ret_stack; 92 /* 93 * This is a case where function graph tracer has 94 * modified a return address (LR) in a stack frame 95 * to hook a function return. 96 * So replace it to an original value. 97 */ 98 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++); 99 if (WARN_ON_ONCE(!ret_stack)) 100 return -EINVAL; 101 frame->pc = ret_stack->ret; 102 } 103 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 104 105 frame->pc = ptrauth_strip_insn_pac(frame->pc); 106 107 /* 108 * Frames created upon entry from EL0 have NULL FP and PC values, so 109 * don't bother reporting these. Frames created by __noreturn functions 110 * might have a valid FP even if PC is bogus, so only terminate where 111 * both are NULL. 112 */ 113 if (!frame->fp && !frame->pc) 114 return -EINVAL; 115 116 return 0; 117 } 118 NOKPROBE_SYMBOL(unwind_frame); 119 120 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame, 121 int (*fn)(struct stackframe *, void *), void *data) 122 { 123 while (1) { 124 int ret; 125 126 if (fn(frame, data)) 127 break; 128 ret = unwind_frame(tsk, frame); 129 if (ret < 0) 130 break; 131 } 132 } 133 NOKPROBE_SYMBOL(walk_stackframe); 134 135 #ifdef CONFIG_STACKTRACE 136 struct stack_trace_data { 137 struct stack_trace *trace; 138 unsigned int no_sched_functions; 139 unsigned int skip; 140 }; 141 142 static int save_trace(struct stackframe *frame, void *d) 143 { 144 struct stack_trace_data *data = d; 145 struct stack_trace *trace = data->trace; 146 unsigned long addr = frame->pc; 147 148 if (data->no_sched_functions && in_sched_functions(addr)) 149 return 0; 150 if (data->skip) { 151 data->skip--; 152 return 0; 153 } 154 155 trace->entries[trace->nr_entries++] = addr; 156 157 return trace->nr_entries >= trace->max_entries; 158 } 159 160 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace) 161 { 162 struct stack_trace_data data; 163 struct stackframe frame; 164 165 data.trace = trace; 166 data.skip = trace->skip; 167 data.no_sched_functions = 0; 168 169 start_backtrace(&frame, regs->regs[29], regs->pc); 170 walk_stackframe(current, &frame, save_trace, &data); 171 } 172 EXPORT_SYMBOL_GPL(save_stack_trace_regs); 173 174 static noinline void __save_stack_trace(struct task_struct *tsk, 175 struct stack_trace *trace, unsigned int nosched) 176 { 177 struct stack_trace_data data; 178 struct stackframe frame; 179 180 if (!try_get_task_stack(tsk)) 181 return; 182 183 data.trace = trace; 184 data.skip = trace->skip; 185 data.no_sched_functions = nosched; 186 187 if (tsk != current) { 188 start_backtrace(&frame, thread_saved_fp(tsk), 189 thread_saved_pc(tsk)); 190 } else { 191 /* We don't want this function nor the caller */ 192 data.skip += 2; 193 start_backtrace(&frame, 194 (unsigned long)__builtin_frame_address(0), 195 (unsigned long)__save_stack_trace); 196 } 197 198 walk_stackframe(tsk, &frame, save_trace, &data); 199 200 put_task_stack(tsk); 201 } 202 EXPORT_SYMBOL_GPL(save_stack_trace_tsk); 203 204 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace) 205 { 206 __save_stack_trace(tsk, trace, 1); 207 } 208 209 void save_stack_trace(struct stack_trace *trace) 210 { 211 __save_stack_trace(current, trace, 0); 212 } 213 214 EXPORT_SYMBOL_GPL(save_stack_trace); 215 #endif 216