arch/arm/kernel/stacktrace.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/export.h>
   3 #include <linux/kprobes.h>
   4 #include <linux/sched.h>
   5 #include <linux/sched/debug.h>
   6 #include <linux/stacktrace.h>
   7
   8 #include <asm/sections.h>
   9 #include <asm/stacktrace.h>
  10 #include <asm/traps.h>
  11
  12 #include "reboot.h"
  13
  14 #if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
  15 /*
  16  * Unwind the current stack frame and store the new register values in the
  17  * structure passed as argument. Unwinding is equivalent to a function return,
  18  * hence the new PC value rather than LR should be used for backtrace.
  19  *
  20  * With framepointer enabled, a simple function prologue looks like this:
  21  *      mov     ip, sp
  22  *      stmdb   sp!, {fp, ip, lr, pc}
  23  *      sub     fp, ip, #4
  24  *
  25  * A simple function epilogue looks like this:
  26  *      ldm     sp, {fp, sp, pc}
  27  *
  28  * When compiled with clang, pc and sp are not pushed. A simple function
  29  * prologue looks like this when built with clang:
  30  *
  31  *      stmdb   {..., fp, lr}
  32  *      add     fp, sp, #x
  33  *      sub     sp, sp, #y
  34  *
  35  * A simple function epilogue looks like this when built with clang:
  36  *
  37  *      sub     sp, fp, #x
  38  *      ldm     {..., fp, pc}
  39  *
  40  *
  41  * Note that with framepointer enabled, even the leaf functions have the same
  42  * prologue and epilogue, therefore we can ignore the LR value in this case.
  43  */
  44
  45 extern unsigned long call_with_stack_end;
  46
  47 static int frame_pointer_check(struct stackframe *frame)
  48 {
  49         unsigned long high, low;
  50         unsigned long fp = frame->fp;
  51         unsigned long pc = frame->pc;
  52
  53         /*
  54          * call_with_stack() is the only place we allow SP to jump from one
  55          * stack to another, with FP and SP pointing to different stacks,
  56          * skipping the FP boundary check at this point.
  57          */
  58         if (pc >= (unsigned long)&call_with_stack &&
  59                         pc < (unsigned long)&call_with_stack_end)
  60                 return 0;
  61
  62         /* only go to a higher address on the stack */
  63         low = frame->sp;
  64         high = ALIGN(low, THREAD_SIZE);
  65
  66         /* check current frame pointer is within bounds */
  67 #ifdef CONFIG_CC_IS_CLANG
  68         if (fp < low + 4 || fp > high - 4)
  69                 return -EINVAL;
  70 #else
  71         if (fp < low + 12 || fp > high - 4)
  72                 return -EINVAL;
  73 #endif
  74
  75         return 0;
  76 }
  77
  78 int notrace unwind_frame(struct stackframe *frame)
  79 {
  80         unsigned long fp = frame->fp;
  81
  82         if (frame_pointer_check(frame))
  83                 return -EINVAL;
  84
  85         /*
  86          * When we unwind through an exception stack, include the saved PC
  87          * value into the stack trace.
  88          */
  89         if (frame->ex_frame) {
  90                 struct pt_regs *regs = (struct pt_regs *)frame->sp;
  91
  92                 /*
  93                  * We check that 'regs + sizeof(struct pt_regs)' (that is,
  94                  * &regs[1]) does not exceed the bottom of the stack to avoid
  95                  * accessing data outside the task's stack. This may happen
  96                  * when frame->ex_frame is a false positive.
  97                  */
  98                 if ((unsigned long)&regs[1] > ALIGN(frame->sp, THREAD_SIZE))
  99                         return -EINVAL;
 100
 101                 frame->pc = regs->ARM_pc;
 102                 frame->ex_frame = false;
 103                 return 0;
 104         }
 105
 106         /* restore the registers from the stack frame */
 107 #ifdef CONFIG_CC_IS_CLANG
 108         frame->sp = frame->fp;
 109         frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 110         frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 4));
 111 #else
 112         frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 12));
 113         frame->sp = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 8));
 114         frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 4));
 115 #endif
 116 #ifdef CONFIG_KRETPROBES
 117         if (is_kretprobe_trampoline(frame->pc))
 118                 frame->pc = kretprobe_find_ret_addr(frame->tsk,
 119                                         (void *)frame->fp, &frame->kr_cur);
 120 #endif
 121
 122         if (in_entry_text(frame->pc))
 123                 frame->ex_frame = true;
 124
 125         return 0;
 126 }
 127 #endif
 128
 129 void notrace walk_stackframe(struct stackframe *frame,
 130                      int (*fn)(struct stackframe *, void *), void *data)
 131 {
 132         while (1) {
 133                 int ret;
 134
 135                 if (fn(frame, data))
 136                         break;
 137                 ret = unwind_frame(frame);
 138                 if (ret < 0)
 139                         break;
 140         }
 141 }
 142 EXPORT_SYMBOL(walk_stackframe);
 143
 144 #ifdef CONFIG_STACKTRACE
 145 struct stack_trace_data {
 146         struct stack_trace *trace;
 147         unsigned int no_sched_functions;
 148         unsigned int skip;
 149 };
 150
 151 static int save_trace(struct stackframe *frame, void *d)
 152 {
 153         struct stack_trace_data *data = d;
 154         struct stack_trace *trace = data->trace;
 155         unsigned long addr = frame->pc;
 156
 157         if (data->no_sched_functions && in_sched_functions(addr))
 158                 return 0;
 159         if (data->skip) {
 160                 data->skip--;
 161                 return 0;
 162         }
 163
 164         trace->entries[trace->nr_entries++] = addr;
 165         return trace->nr_entries >= trace->max_entries;
 166 }
 167
 168 /* This must be noinline to so that our skip calculation works correctly */
 169 static noinline void __save_stack_trace(struct task_struct *tsk,
 170         struct stack_trace *trace, unsigned int nosched)
 171 {
 172         struct stack_trace_data data;
 173         struct stackframe frame;
 174
 175         data.trace = trace;
 176         data.skip = trace->skip;
 177         data.no_sched_functions = nosched;
 178
 179         if (tsk != current) {
 180 #ifdef CONFIG_SMP
 181                 /*
 182                  * What guarantees do we have here that 'tsk' is not
 183                  * running on another CPU?  For now, ignore it as we
 184                  * can't guarantee we won't explode.
 185                  */
 186                 return;
 187 #else
 188                 frame.fp = thread_saved_fp(tsk);
 189                 frame.sp = thread_saved_sp(tsk);
 190                 frame.lr = 0;           /* recovered from the stack */
 191                 frame.pc = thread_saved_pc(tsk);
 192 #endif
 193         } else {
 194                 /* We don't want this function nor the caller */
 195                 data.skip += 2;
 196                 frame.fp = (unsigned long)__builtin_frame_address(0);
 197                 frame.sp = current_stack_pointer;
 198                 frame.lr = (unsigned long)__builtin_return_address(0);
 199 here:
 200                 frame.pc = (unsigned long)&&here;
 201         }
 202 #ifdef CONFIG_KRETPROBES
 203         frame.kr_cur = NULL;
 204         frame.tsk = tsk;
 205 #endif
 206 #ifdef CONFIG_UNWINDER_FRAME_POINTER
 207         frame.ex_frame = false;
 208 #endif
 209
 210         walk_stackframe(&frame, save_trace, &data);
 211 }
 212
 213 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 214 {
 215         struct stack_trace_data data;
 216         struct stackframe frame;
 217
 218         data.trace = trace;
 219         data.skip = trace->skip;
 220         data.no_sched_functions = 0;
 221
 222         frame.fp = regs->ARM_fp;
 223         frame.sp = regs->ARM_sp;
 224         frame.lr = regs->ARM_lr;
 225         frame.pc = regs->ARM_pc;
 226 #ifdef CONFIG_KRETPROBES
 227         frame.kr_cur = NULL;
 228         frame.tsk = current;
 229 #endif
 230 #ifdef CONFIG_UNWINDER_FRAME_POINTER
 231         frame.ex_frame = in_entry_text(frame.pc);
 232 #endif
 233
 234         walk_stackframe(&frame, save_trace, &data);
 235 }
 236
 237 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 238 {
 239         __save_stack_trace(tsk, trace, 1);
 240 }
 241 EXPORT_SYMBOL(save_stack_trace_tsk);
 242
 243 void save_stack_trace(struct stack_trace *trace)
 244 {
 245         __save_stack_trace(current, trace, 0);
 246 }
 247 EXPORT_SYMBOL_GPL(save_stack_trace);
 248 #endif