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 static notrace 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_KRETPROBES 42 frame->kr_cur = NULL; 43 #endif 44 45 /* 46 * Prime the first unwind. 47 * 48 * In unwind_frame() we'll check that the FP points to a valid stack, 49 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be 50 * treated as a transition to whichever stack that happens to be. The 51 * prev_fp value won't be used, but we set it to 0 such that it is 52 * definitely not an accessible stack address. 53 */ 54 bitmap_zero(frame->stacks_done, __NR_STACK_TYPES); 55 frame->prev_fp = 0; 56 frame->prev_type = STACK_TYPE_UNKNOWN; 57 } 58 NOKPROBE_SYMBOL(start_backtrace); 59 60 /* 61 * Unwind from one frame record (A) to the next frame record (B). 62 * 63 * We terminate early if the location of B indicates a malformed chain of frame 64 * records (e.g. a cycle), determined based on the location and fp value of A 65 * and the location (but not the fp value) of B. 66 */ 67 static int notrace unwind_frame(struct task_struct *tsk, 68 struct stackframe *frame) 69 { 70 unsigned long fp = frame->fp; 71 struct stack_info info; 72 73 if (!tsk) 74 tsk = current; 75 76 /* Final frame; nothing to unwind */ 77 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) 78 return -ENOENT; 79 80 if (fp & 0x7) 81 return -EINVAL; 82 83 if (!on_accessible_stack(tsk, fp, 16, &info)) 84 return -EINVAL; 85 86 if (test_bit(info.type, frame->stacks_done)) 87 return -EINVAL; 88 89 /* 90 * As stacks grow downward, any valid record on the same stack must be 91 * at a strictly higher address than the prior record. 92 * 93 * Stacks can nest in several valid orders, e.g. 94 * 95 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 96 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 97 * 98 * ... but the nesting itself is strict. Once we transition from one 99 * stack to another, it's never valid to unwind back to that first 100 * stack. 101 */ 102 if (info.type == frame->prev_type) { 103 if (fp <= frame->prev_fp) 104 return -EINVAL; 105 } else { 106 set_bit(frame->prev_type, frame->stacks_done); 107 } 108 109 /* 110 * Record this frame record's values and location. The prev_fp and 111 * prev_type are only meaningful to the next unwind_frame() invocation. 112 */ 113 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 114 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 115 frame->prev_fp = fp; 116 frame->prev_type = info.type; 117 118 frame->pc = ptrauth_strip_insn_pac(frame->pc); 119 120 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 121 if (tsk->ret_stack && 122 (frame->pc == (unsigned long)return_to_handler)) { 123 unsigned long orig_pc; 124 /* 125 * This is a case where function graph tracer has 126 * modified a return address (LR) in a stack frame 127 * to hook a function return. 128 * So replace it to an original value. 129 */ 130 orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc, 131 (void *)frame->fp); 132 if (WARN_ON_ONCE(frame->pc == orig_pc)) 133 return -EINVAL; 134 frame->pc = orig_pc; 135 } 136 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 137 #ifdef CONFIG_KRETPROBES 138 if (is_kretprobe_trampoline(frame->pc)) 139 frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur); 140 #endif 141 142 return 0; 143 } 144 NOKPROBE_SYMBOL(unwind_frame); 145 146 static void notrace walk_stackframe(struct task_struct *tsk, 147 struct stackframe *frame, 148 bool (*fn)(void *, unsigned long), void *data) 149 { 150 while (1) { 151 int ret; 152 153 if (!fn(data, frame->pc)) 154 break; 155 ret = unwind_frame(tsk, frame); 156 if (ret < 0) 157 break; 158 } 159 } 160 NOKPROBE_SYMBOL(walk_stackframe); 161 162 static bool dump_backtrace_entry(void *arg, unsigned long where) 163 { 164 char *loglvl = arg; 165 printk("%s %pSb\n", loglvl, (void *)where); 166 return true; 167 } 168 169 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 170 const char *loglvl) 171 { 172 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 173 174 if (regs && user_mode(regs)) 175 return; 176 177 if (!tsk) 178 tsk = current; 179 180 if (!try_get_task_stack(tsk)) 181 return; 182 183 printk("%sCall trace:\n", loglvl); 184 arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs); 185 186 put_task_stack(tsk); 187 } 188 189 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl) 190 { 191 dump_backtrace(NULL, tsk, loglvl); 192 barrier(); 193 } 194 195 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, 196 void *cookie, struct task_struct *task, 197 struct pt_regs *regs) 198 { 199 struct stackframe frame; 200 201 if (regs) 202 start_backtrace(&frame, regs->regs[29], regs->pc); 203 else if (task == current) 204 start_backtrace(&frame, 205 (unsigned long)__builtin_frame_address(1), 206 (unsigned long)__builtin_return_address(0)); 207 else 208 start_backtrace(&frame, thread_saved_fp(task), 209 thread_saved_pc(task)); 210 211 walk_stackframe(task, &frame, consume_entry, cookie); 212 } 213