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 #ifdef CONFIG_KRETPROBES 45 frame->kr_cur = NULL; 46 #endif 47 48 /* 49 * Prime the first unwind. 50 * 51 * In unwind_frame() we'll check that the FP points to a valid stack, 52 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be 53 * treated as a transition to whichever stack that happens to be. The 54 * prev_fp value won't be used, but we set it to 0 such that it is 55 * definitely not an accessible stack address. 56 */ 57 bitmap_zero(frame->stacks_done, __NR_STACK_TYPES); 58 frame->prev_fp = 0; 59 frame->prev_type = STACK_TYPE_UNKNOWN; 60 } 61 62 /* 63 * Unwind from one frame record (A) to the next frame record (B). 64 * 65 * We terminate early if the location of B indicates a malformed chain of frame 66 * records (e.g. a cycle), determined based on the location and fp value of A 67 * and the location (but not the fp value) of B. 68 */ 69 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) 70 { 71 unsigned long fp = frame->fp; 72 struct stack_info info; 73 74 if (!tsk) 75 tsk = current; 76 77 /* Final frame; nothing to unwind */ 78 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) 79 return -ENOENT; 80 81 if (fp & 0x7) 82 return -EINVAL; 83 84 if (!on_accessible_stack(tsk, fp, 16, &info)) 85 return -EINVAL; 86 87 if (test_bit(info.type, frame->stacks_done)) 88 return -EINVAL; 89 90 /* 91 * As stacks grow downward, any valid record on the same stack must be 92 * at a strictly higher address than the prior record. 93 * 94 * Stacks can nest in several valid orders, e.g. 95 * 96 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 97 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 98 * 99 * ... but the nesting itself is strict. Once we transition from one 100 * stack to another, it's never valid to unwind back to that first 101 * stack. 102 */ 103 if (info.type == frame->prev_type) { 104 if (fp <= frame->prev_fp) 105 return -EINVAL; 106 } else { 107 set_bit(frame->prev_type, frame->stacks_done); 108 } 109 110 /* 111 * Record this frame record's values and location. The prev_fp and 112 * prev_type are only meaningful to the next unwind_frame() invocation. 113 */ 114 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 115 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 116 frame->prev_fp = fp; 117 frame->prev_type = info.type; 118 119 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 120 if (tsk->ret_stack && 121 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) { 122 struct ftrace_ret_stack *ret_stack; 123 /* 124 * This is a case where function graph tracer has 125 * modified a return address (LR) in a stack frame 126 * to hook a function return. 127 * So replace it to an original value. 128 */ 129 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++); 130 if (WARN_ON_ONCE(!ret_stack)) 131 return -EINVAL; 132 frame->pc = ret_stack->ret; 133 } 134 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 135 #ifdef CONFIG_KRETPROBES 136 if (is_kretprobe_trampoline(frame->pc)) 137 frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur); 138 #endif 139 140 frame->pc = ptrauth_strip_insn_pac(frame->pc); 141 142 return 0; 143 } 144 NOKPROBE_SYMBOL(unwind_frame); 145 146 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame, 147 bool (*fn)(void *, unsigned long), void *data) 148 { 149 while (1) { 150 int ret; 151 152 if (!fn(data, frame->pc)) 153 break; 154 ret = unwind_frame(tsk, frame); 155 if (ret < 0) 156 break; 157 } 158 } 159 NOKPROBE_SYMBOL(walk_stackframe); 160 161 static void dump_backtrace_entry(unsigned long where, const char *loglvl) 162 { 163 printk("%s %pSb\n", loglvl, (void *)where); 164 } 165 166 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 167 const char *loglvl) 168 { 169 struct stackframe frame; 170 int skip = 0; 171 172 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 173 174 if (regs) { 175 if (user_mode(regs)) 176 return; 177 skip = 1; 178 } 179 180 if (!tsk) 181 tsk = current; 182 183 if (!try_get_task_stack(tsk)) 184 return; 185 186 if (tsk == current) { 187 start_backtrace(&frame, 188 (unsigned long)__builtin_frame_address(0), 189 (unsigned long)dump_backtrace); 190 } else { 191 /* 192 * task blocked in __switch_to 193 */ 194 start_backtrace(&frame, 195 thread_saved_fp(tsk), 196 thread_saved_pc(tsk)); 197 } 198 199 printk("%sCall trace:\n", loglvl); 200 do { 201 /* skip until specified stack frame */ 202 if (!skip) { 203 dump_backtrace_entry(frame.pc, loglvl); 204 } else if (frame.fp == regs->regs[29]) { 205 skip = 0; 206 /* 207 * Mostly, this is the case where this function is 208 * called in panic/abort. As exception handler's 209 * stack frame does not contain the corresponding pc 210 * at which an exception has taken place, use regs->pc 211 * instead. 212 */ 213 dump_backtrace_entry(regs->pc, loglvl); 214 } 215 } while (!unwind_frame(tsk, &frame)); 216 217 put_task_stack(tsk); 218 } 219 220 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 221 { 222 dump_backtrace(NULL, tsk, loglvl); 223 barrier(); 224 } 225 226 #ifdef CONFIG_STACKTRACE 227 228 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, 229 void *cookie, struct task_struct *task, 230 struct pt_regs *regs) 231 { 232 struct stackframe frame; 233 234 if (regs) 235 start_backtrace(&frame, regs->regs[29], regs->pc); 236 else if (task == current) 237 start_backtrace(&frame, 238 (unsigned long)__builtin_frame_address(1), 239 (unsigned long)__builtin_return_address(0)); 240 else 241 start_backtrace(&frame, thread_saved_fp(task), 242 thread_saved_pc(task)); 243 244 walk_stackframe(task, &frame, consume_entry, cookie); 245 } 246 247 #endif 248