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 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_FUNCTION_GRAPH_TRACER
  42         frame->graph = 0;
  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 int notrace unwind_frame(struct task_struct *tsk, 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 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 118         if (tsk->ret_stack &&
 119                 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
 120                 struct ftrace_ret_stack *ret_stack;
 121                 /*
 122                  * This is a case where function graph tracer has
 123                  * modified a return address (LR) in a stack frame
 124                  * to hook a function return.
 125                  * So replace it to an original value.
 126                  */
 127                 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
 128                 if (WARN_ON_ONCE(!ret_stack))
 129                         return -EINVAL;
 130                 frame->pc = ret_stack->ret;
 131         }
 132 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 133
 134         frame->pc = ptrauth_strip_insn_pac(frame->pc);
 135
 136         return 0;
 137 }
 138 NOKPROBE_SYMBOL(unwind_frame);
 139
 140 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 141                              bool (*fn)(void *, unsigned long), void *data)
 142 {
 143         while (1) {
 144                 int ret;
 145
 146                 if (!fn(data, frame->pc))
 147                         break;
 148                 ret = unwind_frame(tsk, frame);
 149                 if (ret < 0)
 150                         break;
 151         }
 152 }
 153 NOKPROBE_SYMBOL(walk_stackframe);
 154
 155 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
 156 {
 157         printk("%s %pSb\n", loglvl, (void *)where);
 158 }
 159
 160 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 161                     const char *loglvl)
 162 {
 163         struct stackframe frame;
 164         int skip = 0;
 165
 166         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 167
 168         if (regs) {
 169                 if (user_mode(regs))
 170                         return;
 171                 skip = 1;
 172         }
 173
 174         if (!tsk)
 175                 tsk = current;
 176
 177         if (!try_get_task_stack(tsk))
 178                 return;
 179
 180         if (tsk == current) {
 181                 start_backtrace(&frame,
 182                                 (unsigned long)__builtin_frame_address(0),
 183                                 (unsigned long)dump_backtrace);
 184         } else {
 185                 /*
 186                  * task blocked in __switch_to
 187                  */
 188                 start_backtrace(&frame,
 189                                 thread_saved_fp(tsk),
 190                                 thread_saved_pc(tsk));
 191         }
 192
 193         printk("%sCall trace:\n", loglvl);
 194         do {
 195                 /* skip until specified stack frame */
 196                 if (!skip) {
 197                         dump_backtrace_entry(frame.pc, loglvl);
 198                 } else if (frame.fp == regs->regs[29]) {
 199                         skip = 0;
 200                         /*
 201                          * Mostly, this is the case where this function is
 202                          * called in panic/abort. As exception handler's
 203                          * stack frame does not contain the corresponding pc
 204                          * at which an exception has taken place, use regs->pc
 205                          * instead.
 206                          */
 207                         dump_backtrace_entry(regs->pc, loglvl);
 208                 }
 209         } while (!unwind_frame(tsk, &frame));
 210
 211         put_task_stack(tsk);
 212 }
 213
 214 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 215 {
 216         dump_backtrace(NULL, tsk, loglvl);
 217         barrier();
 218 }
 219
 220 #ifdef CONFIG_STACKTRACE
 221
 222 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 223                               void *cookie, struct task_struct *task,
 224                               struct pt_regs *regs)
 225 {
 226         struct stackframe frame;
 227
 228         if (regs)
 229                 start_backtrace(&frame, regs->regs[29], regs->pc);
 230         else if (task == current)
 231                 start_backtrace(&frame,
 232                                 (unsigned long)__builtin_frame_address(1),
 233                                 (unsigned long)__builtin_return_address(0));
 234         else
 235                 start_backtrace(&frame, thread_saved_fp(task),
 236                                 thread_saved_pc(task));
 237
 238         walk_stackframe(task, &frame, consume_entry, cookie);
 239 }
 240
 241 #endif