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