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  * A snapshot of a frame record or fp/lr register values, along with some
  23  * accounting information necessary for robust unwinding.
  24  *
  25  * @fp:          The fp value in the frame record (or the real fp)
  26  * @pc:          The lr value in the frame record (or the real lr)
  27  *
  28  * @stacks_done: Stacks which have been entirely unwound, for which it is no
  29  *               longer valid to unwind to.
  30  *
  31  * @prev_fp:     The fp that pointed to this frame record, or a synthetic value
  32  *               of 0. This is used to ensure that within a stack, each
  33  *               subsequent frame record is at an increasing address.
  34  * @prev_type:   The type of stack this frame record was on, or a synthetic
  35  *               value of STACK_TYPE_UNKNOWN. This is used to detect a
  36  *               transition from one stack to another.
  37  *
  38  * @kr_cur:      When KRETPROBES is selected, holds the kretprobe instance
  39  *               associated with the most recently encountered replacement lr
  40  *               value.
  41  */
  42 struct unwind_state {
  43         unsigned long fp;
  44         unsigned long pc;
  45         DECLARE_BITMAP(stacks_done, __NR_STACK_TYPES);
  46         unsigned long prev_fp;
  47         enum stack_type prev_type;
  48 #ifdef CONFIG_KRETPROBES
  49         struct llist_node *kr_cur;
  50 #endif
  51 };
  52
  53 static notrace void unwind_init(struct unwind_state *state, unsigned long fp,
  54                                 unsigned long pc)
  55 {
  56         state->fp = fp;
  57         state->pc = pc;
  58 #ifdef CONFIG_KRETPROBES
  59         state->kr_cur = NULL;
  60 #endif
  61
  62         /*
  63          * Prime the first unwind.
  64          *
  65          * In unwind_next() we'll check that the FP points to a valid stack,
  66          * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
  67          * treated as a transition to whichever stack that happens to be. The
  68          * prev_fp value won't be used, but we set it to 0 such that it is
  69          * definitely not an accessible stack address.
  70          */
  71         bitmap_zero(state->stacks_done, __NR_STACK_TYPES);
  72         state->prev_fp = 0;
  73         state->prev_type = STACK_TYPE_UNKNOWN;
  74 }
  75 NOKPROBE_SYMBOL(unwind_init);
  76
  77 /*
  78  * Unwind from one frame record (A) to the next frame record (B).
  79  *
  80  * We terminate early if the location of B indicates a malformed chain of frame
  81  * records (e.g. a cycle), determined based on the location and fp value of A
  82  * and the location (but not the fp value) of B.
  83  */
  84 static int notrace unwind_next(struct task_struct *tsk,
  85                                struct unwind_state *state)
  86 {
  87         unsigned long fp = state->fp;
  88         struct stack_info info;
  89
  90         /* Final frame; nothing to unwind */
  91         if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
  92                 return -ENOENT;
  93
  94         if (fp & 0x7)
  95                 return -EINVAL;
  96
  97         if (!on_accessible_stack(tsk, fp, 16, &info))
  98                 return -EINVAL;
  99
 100         if (test_bit(info.type, state->stacks_done))
 101                 return -EINVAL;
 102
 103         /*
 104          * As stacks grow downward, any valid record on the same stack must be
 105          * at a strictly higher address than the prior record.
 106          *
 107          * Stacks can nest in several valid orders, e.g.
 108          *
 109          * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
 110          * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
 111          *
 112          * ... but the nesting itself is strict. Once we transition from one
 113          * stack to another, it's never valid to unwind back to that first
 114          * stack.
 115          */
 116         if (info.type == state->prev_type) {
 117                 if (fp <= state->prev_fp)
 118                         return -EINVAL;
 119         } else {
 120                 set_bit(state->prev_type, state->stacks_done);
 121         }
 122
 123         /*
 124          * Record this frame record's values and location. The prev_fp and
 125          * prev_type are only meaningful to the next unwind_next() invocation.
 126          */
 127         state->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 128         state->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
 129         state->prev_fp = fp;
 130         state->prev_type = info.type;
 131
 132         state->pc = ptrauth_strip_insn_pac(state->pc);
 133
 134 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 135         if (tsk->ret_stack &&
 136                 (state->pc == (unsigned long)return_to_handler)) {
 137                 unsigned long orig_pc;
 138                 /*
 139                  * This is a case where function graph tracer has
 140                  * modified a return address (LR) in a stack frame
 141                  * to hook a function return.
 142                  * So replace it to an original value.
 143                  */
 144                 orig_pc = ftrace_graph_ret_addr(tsk, NULL, state->pc,
 145                                                 (void *)state->fp);
 146                 if (WARN_ON_ONCE(state->pc == orig_pc))
 147                         return -EINVAL;
 148                 state->pc = orig_pc;
 149         }
 150 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 151 #ifdef CONFIG_KRETPROBES
 152         if (is_kretprobe_trampoline(state->pc))
 153                 state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur);
 154 #endif
 155
 156         return 0;
 157 }
 158 NOKPROBE_SYMBOL(unwind_next);
 159
 160 static void notrace unwind(struct task_struct *tsk,
 161                            struct unwind_state *state,
 162                            stack_trace_consume_fn consume_entry, void *cookie)
 163 {
 164         while (1) {
 165                 int ret;
 166
 167                 if (!consume_entry(cookie, state->pc))
 168                         break;
 169                 ret = unwind_next(tsk, state);
 170                 if (ret < 0)
 171                         break;
 172         }
 173 }
 174 NOKPROBE_SYMBOL(unwind);
 175
 176 static bool dump_backtrace_entry(void *arg, unsigned long where)
 177 {
 178         char *loglvl = arg;
 179         printk("%s %pSb\n", loglvl, (void *)where);
 180         return true;
 181 }
 182
 183 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 184                     const char *loglvl)
 185 {
 186         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 187
 188         if (regs && user_mode(regs))
 189                 return;
 190
 191         if (!tsk)
 192                 tsk = current;
 193
 194         if (!try_get_task_stack(tsk))
 195                 return;
 196
 197         printk("%sCall trace:\n", loglvl);
 198         arch_stack_walk(dump_backtrace_entry, (void *)loglvl, tsk, regs);
 199
 200         put_task_stack(tsk);
 201 }
 202
 203 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
 204 {
 205         dump_backtrace(NULL, tsk, loglvl);
 206         barrier();
 207 }
 208
 209 noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 210                               void *cookie, struct task_struct *task,
 211                               struct pt_regs *regs)
 212 {
 213         struct unwind_state state;
 214
 215         if (regs)
 216                 unwind_init(&state, regs->regs[29], regs->pc);
 217         else if (task == current)
 218                 unwind_init(&state,
 219                                 (unsigned long)__builtin_frame_address(1),
 220                                 (unsigned long)__builtin_return_address(0));
 221         else
 222                 unwind_init(&state, thread_saved_fp(task),
 223                                 thread_saved_pc(task));
 224
 225         unwind(task, &state, consume_entry, cookie);
 226 }