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/sched.h> 11 #include <linux/sched/debug.h> 12 #include <linux/sched/task_stack.h> 13 #include <linux/stacktrace.h> 14 15 #include <asm/irq.h> 16 #include <asm/stack_pointer.h> 17 #include <asm/stacktrace.h> 18 19 /* 20 * Start an unwind from a pt_regs. 21 * 22 * The unwind will begin at the PC within the regs. 23 * 24 * The regs must be on a stack currently owned by the calling task. 25 */ 26 static inline void unwind_init_from_regs(struct unwind_state *state, 27 struct pt_regs *regs) 28 { 29 unwind_init_common(state, current); 30 31 state->fp = regs->regs[29]; 32 state->pc = regs->pc; 33 } 34 35 /* 36 * Start an unwind from a caller. 37 * 38 * The unwind will begin at the caller of whichever function this is inlined 39 * into. 40 * 41 * The function which invokes this must be noinline. 42 */ 43 static __always_inline void unwind_init_from_caller(struct unwind_state *state) 44 { 45 unwind_init_common(state, current); 46 47 state->fp = (unsigned long)__builtin_frame_address(1); 48 state->pc = (unsigned long)__builtin_return_address(0); 49 } 50 51 /* 52 * Start an unwind from a blocked task. 53 * 54 * The unwind will begin at the blocked tasks saved PC (i.e. the caller of 55 * cpu_switch_to()). 56 * 57 * The caller should ensure the task is blocked in cpu_switch_to() for the 58 * duration of the unwind, or the unwind will be bogus. It is never valid to 59 * call this for the current task. 60 */ 61 static inline void unwind_init_from_task(struct unwind_state *state, 62 struct task_struct *task) 63 { 64 unwind_init_common(state, task); 65 66 state->fp = thread_saved_fp(task); 67 state->pc = thread_saved_pc(task); 68 } 69 70 /* 71 * We can only safely access per-cpu stacks from current in a non-preemptible 72 * context. 73 */ 74 static bool on_accessible_stack(const struct task_struct *tsk, 75 unsigned long sp, unsigned long size, 76 struct stack_info *info) 77 { 78 if (info) 79 info->type = STACK_TYPE_UNKNOWN; 80 81 if (on_task_stack(tsk, sp, size, info)) 82 return true; 83 if (tsk != current || preemptible()) 84 return false; 85 if (on_irq_stack(sp, size, info)) 86 return true; 87 if (on_overflow_stack(sp, size, info)) 88 return true; 89 if (on_sdei_stack(sp, size, info)) 90 return true; 91 92 return false; 93 } 94 95 /* 96 * Unwind from one frame record (A) to the next frame record (B). 97 * 98 * We terminate early if the location of B indicates a malformed chain of frame 99 * records (e.g. a cycle), determined based on the location and fp value of A 100 * and the location (but not the fp value) of B. 101 */ 102 static int notrace unwind_next(struct unwind_state *state) 103 { 104 struct task_struct *tsk = state->task; 105 unsigned long fp = state->fp; 106 int err; 107 108 /* Final frame; nothing to unwind */ 109 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) 110 return -ENOENT; 111 112 err = unwind_next_common(state, on_accessible_stack, NULL); 113 if (err) 114 return err; 115 116 state->pc = ptrauth_strip_insn_pac(state->pc); 117 118 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 119 if (tsk->ret_stack && 120 (state->pc == (unsigned long)return_to_handler)) { 121 unsigned long orig_pc; 122 /* 123 * This is a case where function graph tracer has 124 * modified a return address (LR) in a stack frame 125 * to hook a function return. 126 * So replace it to an original value. 127 */ 128 orig_pc = ftrace_graph_ret_addr(tsk, NULL, state->pc, 129 (void *)state->fp); 130 if (WARN_ON_ONCE(state->pc == orig_pc)) 131 return -EINVAL; 132 state->pc = orig_pc; 133 } 134 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 135 #ifdef CONFIG_KRETPROBES 136 if (is_kretprobe_trampoline(state->pc)) 137 state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur); 138 #endif 139 140 return 0; 141 } 142 NOKPROBE_SYMBOL(unwind_next); 143 144 static void notrace unwind(struct unwind_state *state, 145 stack_trace_consume_fn consume_entry, void *cookie) 146 { 147 while (1) { 148 int ret; 149 150 if (!consume_entry(cookie, state->pc)) 151 break; 152 ret = unwind_next(state); 153 if (ret < 0) 154 break; 155 } 156 } 157 NOKPROBE_SYMBOL(unwind); 158 159 static bool dump_backtrace_entry(void *arg, unsigned long where) 160 { 161 char *loglvl = arg; 162 printk("%s %pSb\n", loglvl, (void *)where); 163 return true; 164 } 165 166 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 167 const char *loglvl) 168 { 169 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 170 171 if (regs && user_mode(regs)) 172 return; 173 174 if (!tsk) 175 tsk = current; 176 177 if (!try_get_task_stack(tsk)) 178 return; 179 180 printk("%sCall trace:\n", loglvl); 181 arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs); 182 183 put_task_stack(tsk); 184 } 185 186 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 187 { 188 dump_backtrace(NULL, tsk, loglvl); 189 barrier(); 190 } 191 192 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, 193 void *cookie, struct task_struct *task, 194 struct pt_regs *regs) 195 { 196 struct unwind_state state; 197 198 if (regs) { 199 if (task != current) 200 return; 201 unwind_init_from_regs(&state, regs); 202 } else if (task == current) { 203 unwind_init_from_caller(&state); 204 } else { 205 unwind_init_from_task(&state, task); 206 } 207 208 unwind(&state, consume_entry, cookie); 209 } 210