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/rethook.h> 12 #include <linux/sched.h> 13 #include <linux/sched/debug.h> 14 #include <linux/sched/task_stack.h> 15 #include <linux/stacktrace.h> 16 17 #include <asm/irq.h> 18 #include <asm/pointer_auth.h> 19 #include <asm/stack_pointer.h> 20 #include <asm/stacktrace.h> 21 22 /* 23 * AArch64 PCS assigns the frame pointer to x29. 24 * 25 * A simple function prologue looks like this: 26 * sub sp, sp, #0x10 27 * stp x29, x30, [sp] 28 * mov x29, sp 29 * 30 * A simple function epilogue looks like this: 31 * mov sp, x29 32 * ldp x29, x30, [sp] 33 * add sp, sp, #0x10 34 */ 35 36 37 static notrace void start_backtrace(struct stackframe *frame, unsigned long fp, 38 unsigned long pc) 39 { 40 frame->fp = fp; 41 frame->pc = pc; 42 #if defined(CONFIG_KRETPROBES) || defined(CONFIG_RETHOOK) 43 frame->kr_cur = NULL; 44 #endif 45 46 /* 47 * Prime the first unwind. 48 * 49 * In unwind_frame() we'll check that the FP points to a valid stack, 50 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be 51 * treated as a transition to whichever stack that happens to be. The 52 * prev_fp value won't be used, but we set it to 0 such that it is 53 * definitely not an accessible stack address. 54 */ 55 bitmap_zero(frame->stacks_done, __NR_STACK_TYPES); 56 frame->prev_fp = 0; 57 frame->prev_type = STACK_TYPE_UNKNOWN; 58 } 59 NOKPROBE_SYMBOL(start_backtrace); 60 61 /* 62 * Unwind from one frame record (A) to the next frame record (B). 63 * 64 * We terminate early if the location of B indicates a malformed chain of frame 65 * records (e.g. a cycle), determined based on the location and fp value of A 66 * and the location (but not the fp value) of B. 67 */ 68 static int notrace unwind_frame(struct task_struct *tsk, 69 struct stackframe *frame) 70 { 71 unsigned long fp = frame->fp; 72 struct stack_info info; 73 74 if (!tsk) 75 tsk = current; 76 77 /* Final frame; nothing to unwind */ 78 if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) 79 return -ENOENT; 80 81 if (fp & 0x7) 82 return -EINVAL; 83 84 if (!on_accessible_stack(tsk, fp, 16, &info)) 85 return -EINVAL; 86 87 if (test_bit(info.type, frame->stacks_done)) 88 return -EINVAL; 89 90 /* 91 * As stacks grow downward, any valid record on the same stack must be 92 * at a strictly higher address than the prior record. 93 * 94 * Stacks can nest in several valid orders, e.g. 95 * 96 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL 97 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW 98 * 99 * ... but the nesting itself is strict. Once we transition from one 100 * stack to another, it's never valid to unwind back to that first 101 * stack. 102 */ 103 if (info.type == frame->prev_type) { 104 if (fp <= frame->prev_fp) 105 return -EINVAL; 106 } else { 107 set_bit(frame->prev_type, frame->stacks_done); 108 } 109 110 /* 111 * Record this frame record's values and location. The prev_fp and 112 * prev_type are only meaningful to the next unwind_frame() invocation. 113 */ 114 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp)); 115 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8)); 116 frame->prev_fp = fp; 117 frame->prev_type = info.type; 118 119 frame->pc = ptrauth_strip_insn_pac(frame->pc); 120 121 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 122 if (tsk->ret_stack && 123 (frame->pc == (unsigned long)return_to_handler)) { 124 unsigned long orig_pc; 125 /* 126 * This is a case where function graph tracer has 127 * modified a return address (LR) in a stack frame 128 * to hook a function return. 129 * So replace it to an original value. 130 */ 131 orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc, 132 (void *)frame->fp); 133 if (WARN_ON_ONCE(frame->pc == orig_pc)) 134 return -EINVAL; 135 frame->pc = orig_pc; 136 } 137 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 138 #ifdef CONFIG_KRETPROBES 139 if (is_kretprobe_trampoline(frame->pc)) 140 frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur); 141 #endif 142 #ifdef CONFIG_RETHOOK 143 if (is_rethook_trampoline(frame->pc)) 144 frame->pc = rethook_find_ret_addr(tsk, frame->fp, &frame->kr_cur); 145 #endif 146 147 return 0; 148 } 149 NOKPROBE_SYMBOL(unwind_frame); 150 151 static void notrace walk_stackframe(struct task_struct *tsk, 152 struct stackframe *frame, 153 bool (*fn)(void *, unsigned long), void *data) 154 { 155 while (1) { 156 int ret; 157 158 if (!fn(data, frame->pc)) 159 break; 160 ret = unwind_frame(tsk, frame); 161 if (ret < 0) 162 break; 163 } 164 } 165 NOKPROBE_SYMBOL(walk_stackframe); 166 167 static bool dump_backtrace_entry(void *arg, unsigned long where) 168 { 169 char *loglvl = arg; 170 printk("%s %pSb\n", loglvl, (void *)where); 171 return true; 172 } 173 174 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, 175 const char *loglvl) 176 { 177 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); 178 179 if (regs && user_mode(regs)) 180 return; 181 182 if (!tsk) 183 tsk = current; 184 185 if (!try_get_task_stack(tsk)) 186 return; 187 188 printk("%sCall trace:\n", loglvl); 189 arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs); 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 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, 201 void *cookie, struct task_struct *task, 202 struct pt_regs *regs) 203 { 204 struct stackframe frame; 205 206 if (regs) 207 start_backtrace(&frame, regs->regs[29], regs->pc); 208 else if (task == current) 209 start_backtrace(&frame, 210 (unsigned long)__builtin_frame_address(1), 211 (unsigned long)__builtin_return_address(0)); 212 else 213 start_backtrace(&frame, thread_saved_fp(task), 214 thread_saved_pc(task)); 215 216 walk_stackframe(task, &frame, consume_entry, cookie); 217 } 218