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 static 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 static int notrace unwind_frame(struct task_struct *tsk,
  67                                 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         frame->pc = ptrauth_strip_insn_pac(frame->pc);
 118
 119 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 120         if (tsk->ret_stack &&
 121                 (frame->pc == (unsigned long)return_to_handler)) {
 122                 unsigned long orig_pc;
 123                 /*
 124                  * This is a case where function graph tracer has
 125                  * modified a return address (LR) in a stack frame
 126                  * to hook a function return.
 127                  * So replace it to an original value.
 128                  */
 129                 orig_pc = ftrace_graph_ret_addr(tsk, NULL, frame->pc,
 130                                                 (void *)frame->fp);
 131                 if (WARN_ON_ONCE(frame->pc == orig_pc))
 132                         return -EINVAL;
 133                 frame->pc = orig_pc;
 134         }
 135 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 136 #ifdef CONFIG_KRETPROBES
 137         if (is_kretprobe_trampoline(frame->pc))
 138                 frame->pc = kretprobe_find_ret_addr(tsk, (void *)frame->fp, &frame->kr_cur);
 139 #endif
 140
 141         return 0;
 142 }
 143 NOKPROBE_SYMBOL(unwind_frame);
 144
 145 static void notrace walk_stackframe(struct task_struct *tsk,
 146                                     struct stackframe *frame,
 147                                     bool (*fn)(void *, unsigned long), void *data)
 148 {
 149         while (1) {
 150                 int ret;
 151
 152                 if (!fn(data, frame->pc))
 153                         break;
 154                 ret = unwind_frame(tsk, frame);
 155                 if (ret < 0)
 156                         break;
 157         }
 158 }
 159 NOKPROBE_SYMBOL(walk_stackframe);
 160
 161 static bool dump_backtrace_entry(void *arg, unsigned long where)
 162 {
 163         char *loglvl = arg;
 164         printk("%s %pSb\n", loglvl, (void *)where);
 165         return true;
 166 }
 167
 168 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 169                     const char *loglvl)
 170 {
 171         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 172
 173         if (regs && user_mode(regs))
 174                 return;
 175
 176         if (!tsk)
 177                 tsk = current;
 178
 179         if (!try_get_task_stack(tsk))
 180                 return;
 181
 182         printk("%sCall trace:\n", loglvl);
 183         arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs);
 184
 185         put_task_stack(tsk);
 186 }
 187
 188 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 189 {
 190         dump_backtrace(NULL, tsk, loglvl);
 191         barrier();
 192 }
 193
 194 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 195                               void *cookie, struct task_struct *task,
 196                               struct pt_regs *regs)
 197 {
 198         struct stackframe frame;
 199
 200         if (regs)
 201                 start_backtrace(&frame, regs->regs[29], regs->pc);
 202         else if (task == current)
 203                 start_backtrace(&frame,
 204                                 (unsigned long)__builtin_frame_address(1),
 205                                 (unsigned long)__builtin_return_address(0));
 206         else
 207                 start_backtrace(&frame, thread_saved_fp(task),
 208                                 thread_saved_pc(task));
 209
 210         walk_stackframe(task, &frame, consume_entry, cookie);
 211 }