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         if (fp & 0xf)
  48                 return -EINVAL;
  49
  50         if (!tsk)
  51                 tsk = current;
  52
  53         if (!on_accessible_stack(tsk, fp, &info))
  54                 return -EINVAL;
  55
  56         if (test_bit(info.type, frame->stacks_done))
  57                 return -EINVAL;
  58
  59         /*
  60          * As stacks grow downward, any valid record on the same stack must be
  61          * at a strictly higher address than the prior record.
  62          *
  63          * Stacks can nest in several valid orders, e.g.
  64          *
  65          * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
  66          * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
  67          *
  68          * ... but the nesting itself is strict. Once we transition from one
  69          * stack to another, it's never valid to unwind back to that first
  70          * stack.
  71          */
  72         if (info.type == frame->prev_type) {
  73                 if (fp <= frame->prev_fp)
  74                         return -EINVAL;
  75         } else {
  76                 set_bit(frame->prev_type, frame->stacks_done);
  77         }
  78
  79         /*
  80          * Record this frame record's values and location. The prev_fp and
  81          * prev_type are only meaningful to the next unwind_frame() invocation.
  82          */
  83         frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
  84         frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
  85         frame->prev_fp = fp;
  86         frame->prev_type = info.type;
  87
  88 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
  89         if (tsk->ret_stack &&
  90                 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
  91                 struct ftrace_ret_stack *ret_stack;
  92                 /*
  93                  * This is a case where function graph tracer has
  94                  * modified a return address (LR) in a stack frame
  95                  * to hook a function return.
  96                  * So replace it to an original value.
  97                  */
  98                 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
  99                 if (WARN_ON_ONCE(!ret_stack))
 100                         return -EINVAL;
 101                 frame->pc = ret_stack->ret;
 102         }
 103 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 104
 105         frame->pc = ptrauth_strip_insn_pac(frame->pc);
 106
 107         /*
 108          * Frames created upon entry from EL0 have NULL FP and PC values, so
 109          * don't bother reporting these. Frames created by __noreturn functions
 110          * might have a valid FP even if PC is bogus, so only terminate where
 111          * both are NULL.
 112          */
 113         if (!frame->fp && !frame->pc)
 114                 return -EINVAL;
 115
 116         return 0;
 117 }
 118 NOKPROBE_SYMBOL(unwind_frame);
 119
 120 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 121                      int (*fn)(struct stackframe *, void *), void *data)
 122 {
 123         while (1) {
 124                 int ret;
 125
 126                 if (fn(frame, data))
 127                         break;
 128                 ret = unwind_frame(tsk, frame);
 129                 if (ret < 0)
 130                         break;
 131         }
 132 }
 133 NOKPROBE_SYMBOL(walk_stackframe);
 134
 135 #ifdef CONFIG_STACKTRACE
 136 struct stack_trace_data {
 137         struct stack_trace *trace;
 138         unsigned int no_sched_functions;
 139         unsigned int skip;
 140 };
 141
 142 static int save_trace(struct stackframe *frame, void *d)
 143 {
 144         struct stack_trace_data *data = d;
 145         struct stack_trace *trace = data->trace;
 146         unsigned long addr = frame->pc;
 147
 148         if (data->no_sched_functions && in_sched_functions(addr))
 149                 return 0;
 150         if (data->skip) {
 151                 data->skip--;
 152                 return 0;
 153         }
 154
 155         trace->entries[trace->nr_entries++] = addr;
 156
 157         return trace->nr_entries >= trace->max_entries;
 158 }
 159
 160 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 161 {
 162         struct stack_trace_data data;
 163         struct stackframe frame;
 164
 165         data.trace = trace;
 166         data.skip = trace->skip;
 167         data.no_sched_functions = 0;
 168
 169         start_backtrace(&frame, regs->regs[29], regs->pc);
 170         walk_stackframe(current, &frame, save_trace, &data);
 171 }
 172 EXPORT_SYMBOL_GPL(save_stack_trace_regs);
 173
 174 static noinline void __save_stack_trace(struct task_struct *tsk,
 175         struct stack_trace *trace, unsigned int nosched)
 176 {
 177         struct stack_trace_data data;
 178         struct stackframe frame;
 179
 180         if (!try_get_task_stack(tsk))
 181                 return;
 182
 183         data.trace = trace;
 184         data.skip = trace->skip;
 185         data.no_sched_functions = nosched;
 186
 187         if (tsk != current) {
 188                 start_backtrace(&frame, thread_saved_fp(tsk),
 189                                 thread_saved_pc(tsk));
 190         } else {
 191                 /* We don't want this function nor the caller */
 192                 data.skip += 2;
 193                 start_backtrace(&frame,
 194                                 (unsigned long)__builtin_frame_address(0),
 195                                 (unsigned long)__save_stack_trace);
 196         }
 197
 198         walk_stackframe(tsk, &frame, save_trace, &data);
 199
 200         put_task_stack(tsk);
 201 }
 202 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 203
 204 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 205 {
 206         __save_stack_trace(tsk, trace, 1);
 207 }
 208
 209 void save_stack_trace(struct stack_trace *trace)
 210 {
 211         __save_stack_trace(current, trace, 0);
 212 }
 213
 214 EXPORT_SYMBOL_GPL(save_stack_trace);
 215 #endif