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 (fp & 0xf)
  72                 return -EINVAL;
  73
  74         if (!tsk)
  75                 tsk = current;
  76
  77         if (!on_accessible_stack(tsk, fp, &info))
  78                 return -EINVAL;
  79
  80         if (test_bit(info.type, frame->stacks_done))
  81                 return -EINVAL;
  82
  83         /*
  84          * As stacks grow downward, any valid record on the same stack must be
  85          * at a strictly higher address than the prior record.
  86          *
  87          * Stacks can nest in several valid orders, e.g.
  88          *
  89          * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
  90          * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
  91          *
  92          * ... but the nesting itself is strict. Once we transition from one
  93          * stack to another, it's never valid to unwind back to that first
  94          * stack.
  95          */
  96         if (info.type == frame->prev_type) {
  97                 if (fp <= frame->prev_fp)
  98                         return -EINVAL;
  99         } else {
 100                 set_bit(frame->prev_type, frame->stacks_done);
 101         }
 102
 103         /*
 104          * Record this frame record's values and location. The prev_fp and
 105          * prev_type are only meaningful to the next unwind_frame() invocation.
 106          */
 107         frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 108         frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
 109         frame->prev_fp = fp;
 110         frame->prev_type = info.type;
 111
 112 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 113         if (tsk->ret_stack &&
 114                 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
 115                 struct ftrace_ret_stack *ret_stack;
 116                 /*
 117                  * This is a case where function graph tracer has
 118                  * modified a return address (LR) in a stack frame
 119                  * to hook a function return.
 120                  * So replace it to an original value.
 121                  */
 122                 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
 123                 if (WARN_ON_ONCE(!ret_stack))
 124                         return -EINVAL;
 125                 frame->pc = ret_stack->ret;
 126         }
 127 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 128
 129         frame->pc = ptrauth_strip_insn_pac(frame->pc);
 130
 131         /*
 132          * This is a terminal record, so we have finished unwinding.
 133          */
 134         if (!frame->fp && !frame->pc)
 135                 return -ENOENT;
 136
 137         return 0;
 138 }
 139 NOKPROBE_SYMBOL(unwind_frame);
 140
 141 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 142                              bool (*fn)(void *, unsigned long), void *data)
 143 {
 144         while (1) {
 145                 int ret;
 146
 147                 if (!fn(data, frame->pc))
 148                         break;
 149                 ret = unwind_frame(tsk, frame);
 150                 if (ret < 0)
 151                         break;
 152         }
 153 }
 154 NOKPROBE_SYMBOL(walk_stackframe);
 155
 156 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
 157 {
 158         printk("%s %pS\n", loglvl, (void *)where);
 159 }
 160
 161 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 162                     const char *loglvl)
 163 {
 164         struct stackframe frame;
 165         int skip = 0;
 166
 167         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 168
 169         if (regs) {
 170                 if (user_mode(regs))
 171                         return;
 172                 skip = 1;
 173         }
 174
 175         if (!tsk)
 176                 tsk = current;
 177
 178         if (!try_get_task_stack(tsk))
 179                 return;
 180
 181         if (tsk == current) {
 182                 start_backtrace(&frame,
 183                                 (unsigned long)__builtin_frame_address(0),
 184                                 (unsigned long)dump_backtrace);
 185         } else {
 186                 /*
 187                  * task blocked in __switch_to
 188                  */
 189                 start_backtrace(&frame,
 190                                 thread_saved_fp(tsk),
 191                                 thread_saved_pc(tsk));
 192         }
 193
 194         printk("%sCall trace:\n", loglvl);
 195         do {
 196                 /* skip until specified stack frame */
 197                 if (!skip) {
 198                         dump_backtrace_entry(frame.pc, loglvl);
 199                 } else if (frame.fp == regs->regs[29]) {
 200                         skip = 0;
 201                         /*
 202                          * Mostly, this is the case where this function is
 203                          * called in panic/abort. As exception handler's
 204                          * stack frame does not contain the corresponding pc
 205                          * at which an exception has taken place, use regs->pc
 206                          * instead.
 207                          */
 208                         dump_backtrace_entry(regs->pc, loglvl);
 209                 }
 210         } while (!unwind_frame(tsk, &frame));
 211
 212         put_task_stack(tsk);
 213 }
 214
 215 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 216 {
 217         dump_backtrace(NULL, tsk, loglvl);
 218         barrier();
 219 }
 220
 221 #ifdef CONFIG_STACKTRACE
 222
 223 noinline void arch_stack_walk(stack_trace_consume_fn consume_entry,
 224                               void *cookie, struct task_struct *task,
 225                               struct pt_regs *regs)
 226 {
 227         struct stackframe frame;
 228
 229         if (regs)
 230                 start_backtrace(&frame, regs->regs[29], regs->pc);
 231         else if (task == current)
 232                 start_backtrace(&frame,
 233                                 (unsigned long)__builtin_frame_address(1),
 234                                 (unsigned long)__builtin_return_address(0));
 235         else
 236                 start_backtrace(&frame, thread_saved_fp(task),
 237                                 thread_saved_pc(task));
 238
 239         walk_stackframe(task, &frame, consume_entry, cookie);
 240 }
 241
 242 #endif