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 * A snapshot of a frame record or fp/lr register values, along with some 23 * accounting information necessary for robust unwinding. 24 * 25 * @fp: The fp value in the frame record (or the real fp) 26 * @pc: The lr value in the frame record (or the real lr) 27 * 28 * @stacks_done: Stacks which have been entirely unwound, for which it is no 29 * longer valid to unwind to. 30 * 31 * @prev_fp: The fp that pointed to this frame record, or a synthetic value 32 * of 0. This is used to ensure that within a stack, each 33 * subsequent frame record is at an increasing address. 34 * @prev_type: The type of stack this frame record was on, or a synthetic 35 * value of STACK_TYPE_UNKNOWN. This is used to detect a 36 * transition from one stack to another. 37 * 38 * @kr_cur: When KRETPROBES is selected, holds the kretprobe instance 39 * associated with the most recently encountered replacement lr 40 * value. 41 */ 42 struct stackframe { 43 unsigned long fp; 44 unsigned long pc; 45 DECLARE_BITMAP(stacks_done, __NR_STACK_TYPES); 46 unsigned long prev_fp; 47 enum stack_type prev_type; 48 #ifdef CONFIG_KRETPROBES 49 struct llist_node *kr_cur; 50 #endif 51 }; 52 53 static notrace void start_backtrace(struct stackframe *frame, unsigned long fp, 54 unsigned long pc) 55 { 56 frame->fp = fp; 57 frame->pc = pc; 58 #ifdef CONFIG_KRETPROBES 59 frame->kr_cur = NULL; 60 #endif 61 62 /* 63 * Prime the first unwind. 64 * 65 * In unwind_frame() we'll check that the FP points to a valid stack, 66 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be 67 * treated as a transition to whichever stack that happens to be. The 68 * prev_fp value won't be used, but we set it to 0 such that it is 69 * definitely not an accessible stack address. 70 */ 71 bitmap_zero(frame->stacks_done, __NR_STACK_TYPES); 72 frame->prev_fp = 0; 73 frame->prev_type = STACK_TYPE_UNKNOWN; 74 } 75 NOKPROBE_SYMBOL(start_backtrace); 76 77 /* 78 * Unwind from one frame record (A) to the next frame record (B). 79 * 80 * We terminate early if the location of B indicates a malformed chain of frame 81 * records (e.g. a cycle), determined based on the location and fp value of A 82 * and the location (but not the fp value) of B. 83 */ 84 static int notrace unwind_frame(struct task_struct *tsk, 85 struct stackframe *frame) 86 { 87 unsigned long fp = frame->fp; 88 struct stack_info info; 89 90 /* Final frame; nothing to unwind */ 91 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) 92 return -ENOENT; 93 94 if (fp & 0x7) 95 return -EINVAL; 96 97 if (!on_accessible_stack(tsk, fp, 16, &info)) 98 return -EINVAL; 99 100 if (test_bit(info.type, frame->stacks_done)) 101 return -EINVAL; 102 103 /* 104 * As stacks grow downward, any valid record on the same stack must be 105 * at a strictly higher address than the prior record. 106 * 107 * Stacks can nest in several valid orders, e.g. 108 * 109 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 110 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 111 * 112 * ... but the nesting itself is strict. Once we transition from one 113 * stack to another, it's never valid to unwind back to that first 114 * stack. 115 */ 116 if (info.type == frame->prev_type) { 117 if (fp <= frame->prev_fp) 118 return -EINVAL; 119 } else { 120 set_bit(frame->prev_type, frame->stacks_done); 121 } 122 123 /* 124 * Record this frame record's values and location. The prev_fp and 125 * prev_type are only meaningful to the next unwind_frame() invocation. 126 */ 127 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 128 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 129 frame->prev_fp = fp; 130 frame->prev_type = info.type; 131 132 frame->pc = ptrauth_strip_insn_pac(frame->pc); 133 134 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 135 if (tsk->ret_stack && 136 (frame->pc == (unsigned long)return_to_handler)) { 137 unsigned long orig_pc; 138 /* 139 * This is a case where function graph tracer has 140 * modified a return address (LR) in a stack frame 141 * to hook a function return. 142 * So replace it to an original value. 143 */ 144 orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc, 145 (void *)frame->fp); 146 if (WARN_ON_ONCE(frame->pc == orig_pc)) 147 return -EINVAL; 148 frame->pc = orig_pc; 149 } 150 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 151 #ifdef CONFIG_KRETPROBES 152 if (is_kretprobe_trampoline(frame->pc)) 153 frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur); 154 #endif 155 156 return 0; 157 } 158 NOKPROBE_SYMBOL(unwind_frame); 159 160 static void notrace walk_stackframe(struct task_struct *tsk, 161 struct stackframe *frame, 162 bool (*fn)(void *, unsigned long), void *data) 163 { 164 while (1) { 165 int ret; 166 167 if (!fn(data, frame->pc)) 168 break; 169 ret = unwind_frame(tsk, frame); 170 if (ret < 0) 171 break; 172 } 173 } 174 NOKPROBE_SYMBOL(walk_stackframe); 175 176 static bool dump_backtrace_entry(void *arg, unsigned long where) 177 { 178 char *loglvl = arg; 179 printk("%s %pSb\n", loglvl, (void *)where); 180 return true; 181 } 182 183 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 184 const char *loglvl) 185 { 186 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 187 188 if (regs && user_mode(regs)) 189 return; 190 191 if (!tsk) 192 tsk = current; 193 194 if (!try_get_task_stack(tsk)) 195 return; 196 197 printk("%sCall trace:\n", loglvl); 198 arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs); 199 200 put_task_stack(tsk); 201 } 202 203 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 204 { 205 dump_backtrace(NULL, tsk, loglvl); 206 barrier(); 207 } 208 209 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, 210 void *cookie, struct task_struct *task, 211 struct pt_regs *regs) 212 { 213 struct stackframe frame; 214 215 if (regs) 216 start_backtrace(&frame, regs->regs[29], regs->pc); 217 else if (task == current) 218 start_backtrace(&frame, 219 (unsigned long)__builtin_frame_address(1), 220 (unsigned long)__builtin_return_address(0)); 221 else 222 start_backtrace(&frame, thread_saved_fp(task), 223 thread_saved_pc(task)); 224 225 walk_stackframe(task, &frame, consume_entry, cookie); 226 } 227