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 (!tsk) 72 tsk = current; 73 74 /* Final frame; nothing to unwind */ 75 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) 76 return -ENOENT; 77 78 if (fp & 0x7) 79 return -EINVAL; 80 81 if (!on_accessible_stack(tsk, fp, 16, &info)) 82 return -EINVAL; 83 84 if (test_bit(info.type, frame->stacks_done)) 85 return -EINVAL; 86 87 /* 88 * As stacks grow downward, any valid record on the same stack must be 89 * at a strictly higher address than the prior record. 90 * 91 * Stacks can nest in several valid orders, e.g. 92 * 93 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 94 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 95 * 96 * ... but the nesting itself is strict. Once we transition from one 97 * stack to another, it's never valid to unwind back to that first 98 * stack. 99 */ 100 if (info.type == frame->prev_type) { 101 if (fp <= frame->prev_fp) 102 return -EINVAL; 103 } else { 104 set_bit(frame->prev_type, frame->stacks_done); 105 } 106 107 /* 108 * Record this frame record's values and location. The prev_fp and 109 * prev_type are only meaningful to the next unwind_frame() invocation. 110 */ 111 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 112 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 113 frame->prev_fp = fp; 114 frame->prev_type = info.type; 115 116 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 117 if (tsk->ret_stack && 118 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) { 119 struct ftrace_ret_stack *ret_stack; 120 /* 121 * This is a case where function graph tracer has 122 * modified a return address (LR) in a stack frame 123 * to hook a function return. 124 * So replace it to an original value. 125 */ 126 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++); 127 if (WARN_ON_ONCE(!ret_stack)) 128 return -EINVAL; 129 frame->pc = ret_stack->ret; 130 } 131 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 132 133 frame->pc = ptrauth_strip_insn_pac(frame->pc); 134 135 return 0; 136 } 137 NOKPROBE_SYMBOL(unwind_frame); 138 139 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame, 140 bool (*fn)(void *, unsigned long), void *data) 141 { 142 while (1) { 143 int ret; 144 145 if (!fn(data, frame->pc)) 146 break; 147 ret = unwind_frame(tsk, frame); 148 if (ret < 0) 149 break; 150 } 151 } 152 NOKPROBE_SYMBOL(walk_stackframe); 153 154 static void dump_backtrace_entry(unsigned long where, const char *loglvl) 155 { 156 printk("%s %pSb\n", loglvl, (void *)where); 157 } 158 159 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 160 const char *loglvl) 161 { 162 struct stackframe frame; 163 int skip = 0; 164 165 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 166 167 if (regs) { 168 if (user_mode(regs)) 169 return; 170 skip = 1; 171 } 172 173 if (!tsk) 174 tsk = current; 175 176 if (!try_get_task_stack(tsk)) 177 return; 178 179 if (tsk == current) { 180 start_backtrace(&frame, 181 (unsigned long)__builtin_frame_address(0), 182 (unsigned long)dump_backtrace); 183 } else { 184 /* 185 * task blocked in __switch_to 186 */ 187 start_backtrace(&frame, 188 thread_saved_fp(tsk), 189 thread_saved_pc(tsk)); 190 } 191 192 printk("%sCall trace:\n", loglvl); 193 do { 194 /* skip until specified stack frame */ 195 if (!skip) { 196 dump_backtrace_entry(frame.pc, loglvl); 197 } else if (frame.fp == regs->regs[29]) { 198 skip = 0; 199 /* 200 * Mostly, this is the case where this function is 201 * called in panic/abort. As exception handler's 202 * stack frame does not contain the corresponding pc 203 * at which an exception has taken place, use regs->pc 204 * instead. 205 */ 206 dump_backtrace_entry(regs->pc, loglvl); 207 } 208 } while (!unwind_frame(tsk, &frame)); 209 210 put_task_stack(tsk); 211 } 212 213 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 214 { 215 dump_backtrace(NULL, tsk, loglvl); 216 barrier(); 217 } 218 219 #ifdef CONFIG_STACKTRACE 220 221 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, 222 void *cookie, struct task_struct *task, 223 struct pt_regs *regs) 224 { 225 struct stackframe frame; 226 227 if (regs) 228 start_backtrace(&frame, regs->regs[29], regs->pc); 229 else if (task == current) 230 start_backtrace(&frame, 231 (unsigned long)__builtin_frame_address(1), 232 (unsigned long)__builtin_return_address(0)); 233 else 234 start_backtrace(&frame, thread_saved_fp(task), 235 thread_saved_pc(task)); 236 237 walk_stackframe(task, &frame, consume_entry, cookie); 238 } 239 240 #endif 241