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 void start_backtrace(struct stackframe *frame, unsigned long fp, 37 unsigned long pc) 38 { 39 frame->fp = fp; 40 frame->pc = pc; 41 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 42 frame->graph = 0; 43 #endif 44 45 /* 46 * Prime the first unwind. 47 * 48 * In unwind_frame() we'll check that the FP points to a valid stack, 49 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be 50 * treated as a transition to whichever stack that happens to be. The 51 * prev_fp value won't be used, but we set it to 0 such that it is 52 * definitely not an accessible stack address. 53 */ 54 bitmap_zero(frame->stacks_done, __NR_STACK_TYPES); 55 frame->prev_fp = 0; 56 frame->prev_type = STACK_TYPE_UNKNOWN; 57 } 58 59 /* 60 * Unwind from one frame record (A) to the next frame record (B). 61 * 62 * We terminate early if the location of B indicates a malformed chain of frame 63 * records (e.g. a cycle), determined based on the location and fp value of A 64 * and the location (but not the fp value) of B. 65 */ 66 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) 67 { 68 unsigned long fp = frame->fp; 69 struct stack_info info; 70 71 if (fp & 0xf) 72 return -EINVAL; 73 74 if (!tsk) 75 tsk = current; 76 77 if (!on_accessible_stack(tsk, fp, &info)) 78 return -EINVAL; 79 80 if (test_bit(info.type, frame->stacks_done)) 81 return -EINVAL; 82 83 /* 84 * As stacks grow downward, any valid record on the same stack must be 85 * at a strictly higher address than the prior record. 86 * 87 * Stacks can nest in several valid orders, e.g. 88 * 89 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 90 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 91 * 92 * ... but the nesting itself is strict. Once we transition from one 93 * stack to another, it's never valid to unwind back to that first 94 * stack. 95 */ 96 if (info.type == frame->prev_type) { 97 if (fp <= frame->prev_fp) 98 return -EINVAL; 99 } else { 100 set_bit(frame->prev_type, frame->stacks_done); 101 } 102 103 /* 104 * Record this frame record's values and location. The prev_fp and 105 * prev_type are only meaningful to the next unwind_frame() invocation. 106 */ 107 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 108 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 109 frame->prev_fp = fp; 110 frame->prev_type = info.type; 111 112 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 113 if (tsk->ret_stack && 114 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) { 115 struct ftrace_ret_stack *ret_stack; 116 /* 117 * This is a case where function graph tracer has 118 * modified a return address (LR) in a stack frame 119 * to hook a function return. 120 * So replace it to an original value. 121 */ 122 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++); 123 if (WARN_ON_ONCE(!ret_stack)) 124 return -EINVAL; 125 frame->pc = ret_stack->ret; 126 } 127 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 128 129 frame->pc = ptrauth_strip_insn_pac(frame->pc); 130 131 /* 132 * This is a terminal record, so we have finished unwinding. 133 */ 134 if (!frame->fp && !frame->pc) 135 return -ENOENT; 136 137 return 0; 138 } 139 NOKPROBE_SYMBOL(unwind_frame); 140 141 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame, 142 bool (*fn)(void *, unsigned long), void *data) 143 { 144 while (1) { 145 int ret; 146 147 if (!fn(data, frame->pc)) 148 break; 149 ret = unwind_frame(tsk, frame); 150 if (ret < 0) 151 break; 152 } 153 } 154 NOKPROBE_SYMBOL(walk_stackframe); 155 156 static void dump_backtrace_entry(unsigned long where, const char *loglvl) 157 { 158 printk("%s %pS\n", loglvl, (void *)where); 159 } 160 161 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 162 const char *loglvl) 163 { 164 struct stackframe frame; 165 int skip = 0; 166 167 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 168 169 if (regs) { 170 if (user_mode(regs)) 171 return; 172 skip = 1; 173 } 174 175 if (!tsk) 176 tsk = current; 177 178 if (!try_get_task_stack(tsk)) 179 return; 180 181 if (tsk == current) { 182 start_backtrace(&frame, 183 (unsigned long)__builtin_frame_address(0), 184 (unsigned long)dump_backtrace); 185 } else { 186 /* 187 * task blocked in __switch_to 188 */ 189 start_backtrace(&frame, 190 thread_saved_fp(tsk), 191 thread_saved_pc(tsk)); 192 } 193 194 printk("%sCall trace:\n", loglvl); 195 do { 196 /* skip until specified stack frame */ 197 if (!skip) { 198 dump_backtrace_entry(frame.pc, loglvl); 199 } else if (frame.fp == regs->regs[29]) { 200 skip = 0; 201 /* 202 * Mostly, this is the case where this function is 203 * called in panic/abort. As exception handler's 204 * stack frame does not contain the corresponding pc 205 * at which an exception has taken place, use regs->pc 206 * instead. 207 */ 208 dump_backtrace_entry(regs->pc, loglvl); 209 } 210 } while (!unwind_frame(tsk, &frame)); 211 212 put_task_stack(tsk); 213 } 214 215 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 216 { 217 dump_backtrace(NULL, tsk, loglvl); 218 barrier(); 219 } 220 221 #ifdef CONFIG_STACKTRACE 222 223 noinline void arch_stack_walk(stack_trace_consume_fn consume_entry, 224 void *cookie, struct task_struct *task, 225 struct pt_regs *regs) 226 { 227 struct stackframe frame; 228 229 if (regs) 230 start_backtrace(&frame, regs->regs[29], regs->pc); 231 else if (task == current) 232 start_backtrace(&frame, 233 (unsigned long)__builtin_frame_address(1), 234 (unsigned long)__builtin_return_address(0)); 235 else 236 start_backtrace(&frame, thread_saved_fp(task), 237 thread_saved_pc(task)); 238 239 walk_stackframe(task, &frame, consume_entry, cookie); 240 } 241 242 #endif 243