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 bool (*fn)(void *, unsigned long), void *data) 122 { 123 while (1) { 124 int ret; 125 126 if (!fn(data, frame->pc)) 127 break; 128 ret = unwind_frame(tsk, frame); 129 if (ret < 0) 130 break; 131 } 132 } 133 NOKPROBE_SYMBOL(walk_stackframe); 134 135 static void dump_backtrace_entry(unsigned long where, const char *loglvl) 136 { 137 printk("%s %pS\n", loglvl, (void *)where); 138 } 139 140 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 141 const char *loglvl) 142 { 143 struct stackframe frame; 144 int skip = 0; 145 146 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 147 148 if (regs) { 149 if (user_mode(regs)) 150 return; 151 skip = 1; 152 } 153 154 if (!tsk) 155 tsk = current; 156 157 if (!try_get_task_stack(tsk)) 158 return; 159 160 if (tsk == current) { 161 start_backtrace(&frame, 162 (unsigned long)__builtin_frame_address(0), 163 (unsigned long)dump_backtrace); 164 } else { 165 /* 166 * task blocked in __switch_to 167 */ 168 start_backtrace(&frame, 169 thread_saved_fp(tsk), 170 thread_saved_pc(tsk)); 171 } 172 173 printk("%sCall trace:\n", loglvl); 174 do { 175 /* skip until specified stack frame */ 176 if (!skip) { 177 dump_backtrace_entry(frame.pc, loglvl); 178 } else if (frame.fp == regs->regs[29]) { 179 skip = 0; 180 /* 181 * Mostly, this is the case where this function is 182 * called in panic/abort. As exception handler's 183 * stack frame does not contain the corresponding pc 184 * at which an exception has taken place, use regs->pc 185 * instead. 186 */ 187 dump_backtrace_entry(regs->pc, loglvl); 188 } 189 } while (!unwind_frame(tsk, &frame)); 190 191 put_task_stack(tsk); 192 } 193 194 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 195 { 196 dump_backtrace(NULL, tsk, loglvl); 197 barrier(); 198 } 199 200 #ifdef CONFIG_STACKTRACE 201 202 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie, 203 struct task_struct *task, struct pt_regs *regs) 204 { 205 struct stackframe frame; 206 207 if (regs) 208 start_backtrace(&frame, regs->regs[29], regs->pc); 209 else if (task == current) 210 start_backtrace(&frame, 211 (unsigned long)__builtin_frame_address(0), 212 (unsigned long)arch_stack_walk); 213 else 214 start_backtrace(&frame, thread_saved_fp(task), 215 thread_saved_pc(task)); 216 217 walk_stackframe(task, &frame, consume_entry, cookie); 218 } 219 220 #endif 221