arch/arm64/kernel/stacktrace.c

   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  * Unwind from one frame record (A) to the next frame record (B).
  37  *
  38  * We terminate early if the location of B indicates a malformed chain of frame
  39  * records (e.g. a cycle), determined based on the location and fp value of A
  40  * and the location (but not the fp value) of B.
  41  */
  42 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
  43 {
  44         unsigned long fp = frame->fp;
  45         struct stack_info info;
  46
  47         /* Terminal record; nothing to unwind */
  48         if (!fp)
  49                 return -EINVAL;
  50
  51         if (fp & 0xf)
  52                 return -EINVAL;
  53
  54         if (!tsk)
  55                 tsk = current;
  56
  57         if (!on_accessible_stack(tsk, fp, &info))
  58                 return -EINVAL;
  59
  60         if (test_bit(info.type, frame->stacks_done))
  61                 return -EINVAL;
  62
  63         /*
  64          * As stacks grow downward, any valid record on the same stack must be
  65          * at a strictly higher address than the prior record.
  66          *
  67          * Stacks can nest in several valid orders, e.g.
  68          *
  69          * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
  70          * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
  71          *
  72          * ... but the nesting itself is strict. Once we transition from one
  73          * stack to another, it's never valid to unwind back to that first
  74          * stack.
  75          */
  76         if (info.type == frame->prev_type) {
  77                 if (fp <= frame->prev_fp)
  78                         return -EINVAL;
  79         } else {
  80                 set_bit(frame->prev_type, frame->stacks_done);
  81         }
  82
  83         /*
  84          * Record this frame record's values and location. The prev_fp and
  85          * prev_type are only meaningful to the next unwind_frame() invocation.
  86          */
  87         frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
  88         frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
  89         frame->prev_fp = fp;
  90         frame->prev_type = info.type;
  91
  92 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
  93         if (tsk->ret_stack &&
  94                 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
  95                 struct ftrace_ret_stack *ret_stack;
  96                 /*
  97                  * This is a case where function graph tracer has
  98                  * modified a return address (LR) in a stack frame
  99                  * to hook a function return.
 100                  * So replace it to an original value.
 101                  */
 102                 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
 103                 if (WARN_ON_ONCE(!ret_stack))
 104                         return -EINVAL;
 105                 frame->pc = ret_stack->ret;
 106         }
 107 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 108
 109         frame->pc = ptrauth_strip_insn_pac(frame->pc);
 110
 111         return 0;
 112 }
 113 NOKPROBE_SYMBOL(unwind_frame);
 114
 115 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 116                              bool (*fn)(void *, unsigned long), void *data)
 117 {
 118         while (1) {
 119                 int ret;
 120
 121                 if (!fn(data, frame->pc))
 122                         break;
 123                 ret = unwind_frame(tsk, frame);
 124                 if (ret < 0)
 125                         break;
 126         }
 127 }
 128 NOKPROBE_SYMBOL(walk_stackframe);
 129
 130 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
 131 {
 132         printk("%s %pS\n", loglvl, (void *)where);
 133 }
 134
 135 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 136                     const char *loglvl)
 137 {
 138         struct stackframe frame;
 139         int skip = 0;
 140
 141         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 142
 143         if (regs) {
 144                 if (user_mode(regs))
 145                         return;
 146                 skip = 1;
 147         }
 148
 149         if (!tsk)
 150                 tsk = current;
 151
 152         if (!try_get_task_stack(tsk))
 153                 return;
 154
 155         if (tsk == current) {
 156                 start_backtrace(&frame,
 157                                 (unsigned long)__builtin_frame_address(0),
 158                                 (unsigned long)dump_backtrace);
 159         } else {
 160                 /*
 161                  * task blocked in __switch_to
 162                  */
 163                 start_backtrace(&frame,
 164                                 thread_saved_fp(tsk),
 165                                 thread_saved_pc(tsk));
 166         }
 167
 168         printk("%sCall trace:\n", loglvl);
 169         do {
 170                 /* skip until specified stack frame */
 171                 if (!skip) {
 172                         dump_backtrace_entry(frame.pc, loglvl);
 173                 } else if (frame.fp == regs->regs[29]) {
 174                         skip = 0;
 175                         /*
 176                          * Mostly, this is the case where this function is
 177                          * called in panic/abort. As exception handler's
 178                          * stack frame does not contain the corresponding pc
 179                          * at which an exception has taken place, use regs->pc
 180                          * instead.
 181                          */
 182                         dump_backtrace_entry(regs->pc, loglvl);
 183                 }
 184         } while (!unwind_frame(tsk, &frame));
 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 #ifdef CONFIG_STACKTRACE
 196
 197 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 198                      struct task_struct *task, struct pt_regs *regs)
 199 {
 200         struct stackframe frame;
 201
 202         if (regs)
 203                 start_backtrace(&frame, regs->regs[29], regs->pc);
 204         else if (task == current)
 205                 start_backtrace(&frame,
 206                                 (unsigned long)__builtin_frame_address(0),
 207                                 (unsigned long)arch_stack_walk);
 208         else
 209                 start_backtrace(&frame, thread_saved_fp(task),
 210                                 thread_saved_pc(task));
 211
 212         walk_stackframe(task, &frame, consume_entry, cookie);
 213 }
 214
 215 #endif