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                              bool (*fn)(void *, unsigned long), void *data)
 122 {
 123         while (1) {
 124                 int ret;
 125
 126                 if (!fn(data, frame->pc))
 127                         break;
 128                 ret = unwind_frame(tsk, frame);
 129                 if (ret < 0)
 130                         break;
 131         }
 132 }
 133 NOKPROBE_SYMBOL(walk_stackframe);
 134
 135 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
 136 {
 137         printk("%s %pS\n", loglvl, (void *)where);
 138 }
 139
 140 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 141                     const char *loglvl)
 142 {
 143         struct stackframe frame;
 144         int skip = 0;
 145
 146         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 147
 148         if (regs) {
 149                 if (user_mode(regs))
 150                         return;
 151                 skip = 1;
 152         }
 153
 154         if (!tsk)
 155                 tsk = current;
 156
 157         if (!try_get_task_stack(tsk))
 158                 return;
 159
 160         if (tsk == current) {
 161                 start_backtrace(&frame,
 162                                 (unsigned long)__builtin_frame_address(0),
 163                                 (unsigned long)dump_backtrace);
 164         } else {
 165                 /*
 166                  * task blocked in __switch_to
 167                  */
 168                 start_backtrace(&frame,
 169                                 thread_saved_fp(tsk),
 170                                 thread_saved_pc(tsk));
 171         }
 172
 173         printk("%sCall trace:\n", loglvl);
 174         do {
 175                 /* skip until specified stack frame */
 176                 if (!skip) {
 177                         dump_backtrace_entry(frame.pc, loglvl);
 178                 } else if (frame.fp == regs->regs[29]) {
 179                         skip = 0;
 180                         /*
 181                          * Mostly, this is the case where this function is
 182                          * called in panic/abort. As exception handler's
 183                          * stack frame does not contain the corresponding pc
 184                          * at which an exception has taken place, use regs->pc
 185                          * instead.
 186                          */
 187                         dump_backtrace_entry(regs->pc, loglvl);
 188                 }
 189         } while (!unwind_frame(tsk, &frame));
 190
 191         put_task_stack(tsk);
 192 }
 193
 194 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 195 {
 196         dump_backtrace(NULL, tsk, loglvl);
 197         barrier();
 198 }
 199
 200 #ifdef CONFIG_STACKTRACE
 201
 202 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 203                      struct task_struct *task, struct pt_regs *regs)
 204 {
 205         struct stackframe frame;
 206
 207         if (regs)
 208                 start_backtrace(&frame, regs->regs[29], regs->pc);
 209         else if (task == current)
 210                 start_backtrace(&frame,
 211                                 (unsigned long)__builtin_frame_address(0),
 212                                 (unsigned long)arch_stack_walk);
 213         else
 214                 start_backtrace(&frame, thread_saved_fp(task),
 215                                 thread_saved_pc(task));
 216
 217         walk_stackframe(task, &frame, consume_entry, cookie);
 218 }
 219
 220 #endif