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 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
  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 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
  67 {
  68         unsigned long fp = frame->fp;
  69         struct stack_info info;
  70
  71         if (!tsk)
  72                 tsk = current;
  73
  74         /* Final frame; nothing to unwind */
  75         if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
  76                 return -ENOENT;
  77
  78         if (fp & 0x7)
  79                 return -EINVAL;
  80
  81         if (!on_accessible_stack(tsk, fp, 16, &info))
  82                 return -EINVAL;
  83
  84         if (test_bit(info.type, frame->stacks_done))
  85                 return -EINVAL;
  86
  87         /*
  88          * As stacks grow downward, any valid record on the same stack must be
  89          * at a strictly higher address than the prior record.
  90          *
  91          * Stacks can nest in several valid orders, e.g.
  92          *
  93          * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
  94          * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
  95          *
  96          * ... but the nesting itself is strict. Once we transition from one
  97          * stack to another, it's never valid to unwind back to that first
  98          * stack.
  99          */
 100         if (info.type == frame->prev_type) {
 101                 if (fp <= frame->prev_fp)
 102                         return -EINVAL;
 103         } else {
 104                 set_bit(frame->prev_type, frame->stacks_done);
 105         }
 106
 107         /*
 108          * Record this frame record's values and location. The prev_fp and
 109          * prev_type are only meaningful to the next unwind_frame() invocation.
 110          */
 111         frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 112         frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
 113         frame->prev_fp = fp;
 114         frame->prev_type = info.type;
 115
 116 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 117         if (tsk->ret_stack &&
 118                 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
 119                 struct ftrace_ret_stack *ret_stack;
 120                 /*
 121                  * This is a case where function graph tracer has
 122                  * modified a return address (LR) in a stack frame
 123                  * to hook a function return.
 124                  * So replace it to an original value.
 125                  */
 126                 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
 127                 if (WARN_ON_ONCE(!ret_stack))
 128                         return -EINVAL;
 129                 frame->pc = ret_stack->ret;
 130         }
 131 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 132
 133         frame->pc = ptrauth_strip_insn_pac(frame->pc);
 134
 135         return 0;
 136 }
 137 NOKPROBE_SYMBOL(unwind_frame);
 138
 139 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 140                              bool (*fn)(void *, unsigned long), void *data)
 141 {
 142         while (1) {
 143                 int ret;
 144
 145                 if (!fn(data, frame->pc))
 146                         break;
 147                 ret = unwind_frame(tsk, frame);
 148                 if (ret < 0)
 149                         break;
 150         }
 151 }
 152 NOKPROBE_SYMBOL(walk_stackframe);
 153
 154 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
 155 {
 156         printk("%s %pSb\n", loglvl, (void *)where);
 157 }
 158
 159 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 160                     const char *loglvl)
 161 {
 162         struct stackframe frame;
 163         int skip = 0;
 164
 165         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 166
 167         if (regs) {
 168                 if (user_mode(regs))
 169                         return;
 170                 skip = 1;
 171         }
 172
 173         if (!tsk)
 174                 tsk = current;
 175
 176         if (!try_get_task_stack(tsk))
 177                 return;
 178
 179         if (tsk == current) {
 180                 start_backtrace(&frame,
 181                                 (unsigned long)__builtin_frame_address(0),
 182                                 (unsigned long)dump_backtrace);
 183         } else {
 184                 /*
 185                  * task blocked in __switch_to
 186                  */
 187                 start_backtrace(&frame,
 188                                 thread_saved_fp(tsk),
 189                                 thread_saved_pc(tsk));
 190         }
 191
 192         printk("%sCall trace:\n", loglvl);
 193         do {
 194                 /* skip until specified stack frame */
 195                 if (!skip) {
 196                         dump_backtrace_entry(frame.pc, loglvl);
 197                 } else if (frame.fp == regs->regs[29]) {
 198                         skip = 0;
 199                         /*
 200                          * Mostly, this is the case where this function is
 201                          * called in panic/abort. As exception handler's
 202                          * stack frame does not contain the corresponding pc
 203                          * at which an exception has taken place, use regs->pc
 204                          * instead.
 205                          */
 206                         dump_backtrace_entry(regs->pc, loglvl);
 207                 }
 208         } while (!unwind_frame(tsk, &frame));
 209
 210         put_task_stack(tsk);
 211 }
 212
 213 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 214 {
 215         dump_backtrace(NULL, tsk, loglvl);
 216         barrier();
 217 }
 218
 219 #ifdef CONFIG_STACKTRACE
 220
 221 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 222                               void *cookie, struct task_struct *task,
 223                               struct pt_regs *regs)
 224 {
 225         struct stackframe frame;
 226
 227         if (regs)
 228                 start_backtrace(&frame, regs->regs[29], regs->pc);
 229         else if (task == current)
 230                 start_backtrace(&frame,
 231                                 (unsigned long)__builtin_frame_address(1),
 232                                 (unsigned long)__builtin_return_address(0));
 233         else
 234                 start_backtrace(&frame, thread_saved_fp(task),
 235                                 thread_saved_pc(task));
 236
 237         walk_stackframe(task, &frame, consume_entry, cookie);
 238 }
 239
 240 #endif