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_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 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         frame->pc = ptrauth_strip_insn_pac(frame->pc);
 117
 118 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 119         if (tsk->ret_stack &&
 120                 (frame->pc == (unsigned long)return_to_handler)) {
 121                 unsigned long orig_pc;
 122                 /*
 123                  * This is a case where function graph tracer has
 124                  * modified a return address (LR) in a stack frame
 125                  * to hook a function return.
 126                  * So replace it to an original value.
 127                  */
 128                 orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc,
 129                                                 (void *)frame->fp);
 130                 if (WARN_ON_ONCE(frame->pc == orig_pc))
 131                         return -EINVAL;
 132                 frame->pc = orig_pc;
 133         }
 134 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 135 #ifdef CONFIG_KRETPROBES
 136         if (is_kretprobe_trampoline(frame->pc))
 137                 frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
 138 #endif
 139
 140         return 0;
 141 }
 142 NOKPROBE_SYMBOL(unwind_frame);
 143
 144 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 145                              bool (*fn)(void *, unsigned long), void *data)
 146 {
 147         while (1) {
 148                 int ret;
 149
 150                 if (!fn(data, frame->pc))
 151                         break;
 152                 ret = unwind_frame(tsk, frame);
 153                 if (ret < 0)
 154                         break;
 155         }
 156 }
 157 NOKPROBE_SYMBOL(walk_stackframe);
 158
 159 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
 160 {
 161         printk("%s %pSb\n", loglvl, (void *)where);
 162 }
 163
 164 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 165                     const char *loglvl)
 166 {
 167         struct stackframe frame;
 168         int skip = 0;
 169
 170         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 171
 172         if (regs) {
 173                 if (user_mode(regs))
 174                         return;
 175                 skip = 1;
 176         }
 177
 178         if (!tsk)
 179                 tsk = current;
 180
 181         if (!try_get_task_stack(tsk))
 182                 return;
 183
 184         if (tsk == current) {
 185                 start_backtrace(&frame,
 186                                 (unsigned long)__builtin_frame_address(0),
 187                                 (unsigned long)dump_backtrace);
 188         } else {
 189                 /*
 190                  * task blocked in __switch_to
 191                  */
 192                 start_backtrace(&frame,
 193                                 thread_saved_fp(tsk),
 194                                 thread_saved_pc(tsk));
 195         }
 196
 197         printk("%sCall trace:\n", loglvl);
 198         do {
 199                 /* skip until specified stack frame */
 200                 if (!skip) {
 201                         dump_backtrace_entry(frame.pc, loglvl);
 202                 } else if (frame.fp == regs->regs[29]) {
 203                         skip = 0;
 204                         /*
 205                          * Mostly, this is the case where this function is
 206                          * called in panic/abort. As exception handler's
 207                          * stack frame does not contain the corresponding pc
 208                          * at which an exception has taken place, use regs->pc
 209                          * instead.
 210                          */
 211                         dump_backtrace_entry(regs->pc, loglvl);
 212                 }
 213         } while (!unwind_frame(tsk, &frame));
 214
 215         put_task_stack(tsk);
 216 }
 217
 218 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 219 {
 220         dump_backtrace(NULL, tsk, loglvl);
 221         barrier();
 222 }
 223
 224 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 225                               void *cookie, struct task_struct *task,
 226                               struct pt_regs *regs)
 227 {
 228         struct stackframe frame;
 229
 230         if (regs)
 231                 start_backtrace(&frame, regs->regs[29], regs->pc);
 232         else if (task == current)
 233                 start_backtrace(&frame,
 234                                 (unsigned long)__builtin_frame_address(1),
 235                                 (unsigned long)__builtin_return_address(0));
 236         else
 237                 start_backtrace(&frame, thread_saved_fp(task),
 238                                 thread_saved_pc(task));
 239
 240         walk_stackframe(task, &frame, consume_entry, cookie);
 241 }