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 struct stack_info info; 107 int err; 108 109 /* Final frame; nothing to unwind */ 110 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) 111 return -ENOENT; 112 113 err = unwind_next_common(state, &info, on_accessible_stack, NULL); 114 if (err) 115 return err; 116 117 state->pc = ptrauth_strip_insn_pac(state->pc); 118 119 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 120 if (tsk->ret_stack && 121 (state->pc == (unsigned long)return_to_handler)) { 122 unsigned long orig_pc; 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 orig_pc = ftrace_graph_ret_addr(tsk, NULL, state->pc, 130 (void *)state->fp); 131 if (WARN_ON_ONCE(state->pc == orig_pc)) 132 return -EINVAL; 133 state->pc = orig_pc; 134 } 135 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 136 #ifdef CONFIG_KRETPROBES 137 if (is_kretprobe_trampoline(state->pc)) 138 state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur); 139 #endif 140 141 return 0; 142 } 143 NOKPROBE_SYMBOL(unwind_next); 144 145 static void notrace unwind(struct unwind_state *state, 146 stack_trace_consume_fn consume_entry, void *cookie) 147 { 148 while (1) { 149 int ret; 150 151 if (!consume_entry(cookie, state->pc)) 152 break; 153 ret = unwind_next(state); 154 if (ret < 0) 155 break; 156 } 157 } 158 NOKPROBE_SYMBOL(unwind); 159 160 static bool dump_backtrace_entry(void *arg, unsigned long where) 161 { 162 char *loglvl = arg; 163 printk("%s %pSb\n", loglvl, (void *)where); 164 return true; 165 } 166 167 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 168 const char *loglvl) 169 { 170 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 171 172 if (regs && user_mode(regs)) 173 return; 174 175 if (!tsk) 176 tsk = current; 177 178 if (!try_get_task_stack(tsk)) 179 return; 180 181 printk("%sCall trace:\n", loglvl); 182 arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs); 183 184 put_task_stack(tsk); 185 } 186 187 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 188 { 189 dump_backtrace(NULL, tsk, loglvl); 190 barrier(); 191 } 192 193 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, 194 void *cookie, struct task_struct *task, 195 struct pt_regs *regs) 196 { 197 struct unwind_state state; 198 199 if (regs) { 200 if (task != current) 201 return; 202 unwind_init_from_regs(&state, regs); 203 } else if (task == current) { 204 unwind_init_from_caller(&state); 205 } else { 206 unwind_init_from_task(&state, task); 207 } 208 209 unwind(&state, consume_entry, cookie); 210 } 211