arch/x86/kernel/unwind_frame.c

   1 #include <linux/sched.h>
   2 #include <linux/sched/task.h>
   3 #include <linux/sched/task_stack.h>
   4 #include <linux/interrupt.h>
   5 #include <asm/sections.h>
   6 #include <asm/ptrace.h>
   7 #include <asm/bitops.h>
   8 #include <asm/stacktrace.h>
   9 #include <asm/unwind.h>
  10
  11 #define FRAME_HEADER_SIZE (sizeof(long) * 2)
  12
  13 unsigned long unwind_get_return_address(struct unwind_state *state)
  14 {
  15         if (unwind_done(state))
  16                 return 0;
  17
  18         return __kernel_text_address(state->ip) ? state->ip : 0;
  19 }
  20 EXPORT_SYMBOL_GPL(unwind_get_return_address);
  21
  22 unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
  23 {
  24         if (unwind_done(state))
  25                 return NULL;
  26
  27         return state->regs ? &state->regs->ip : state->bp + 1;
  28 }
  29
  30 static void unwind_dump(struct unwind_state *state)
  31 {
  32         static bool dumped_before = false;
  33         bool prev_zero, zero = false;
  34         unsigned long word, *sp;
  35         struct stack_info stack_info = {0};
  36         unsigned long visit_mask = 0;
  37
  38         if (dumped_before)
  39                 return;
  40
  41         dumped_before = true;
  42
  43         printk_deferred("unwind stack type:%d next_sp:%p mask:0x%lx graph_idx:%d\n",
  44                         state->stack_info.type, state->stack_info.next_sp,
  45                         state->stack_mask, state->graph_idx);
  46
  47         for (sp = PTR_ALIGN(state->orig_sp, sizeof(long)); sp;
  48              sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
  49                 if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
  50                         break;
  51
  52                 for (; sp < stack_info.end; sp++) {
  53
  54                         word = READ_ONCE_NOCHECK(*sp);
  55
  56                         prev_zero = zero;
  57                         zero = word == 0;
  58
  59                         if (zero) {
  60                                 if (!prev_zero)
  61                                         printk_deferred("%p: %0*x ...\n",
  62                                                         sp, BITS_PER_LONG/4, 0);
  63                                 continue;
  64                         }
  65
  66                         printk_deferred("%p: %0*lx (%pB)\n",
  67                                         sp, BITS_PER_LONG/4, word, (void *)word);
  68                 }
  69         }
  70 }
  71
  72 static size_t regs_size(struct pt_regs *regs)
  73 {
  74         /* x86_32 regs from kernel mode are two words shorter: */
  75         if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs))
  76                 return sizeof(*regs) - 2*sizeof(long);
  77
  78         return sizeof(*regs);
  79 }
  80
  81 static bool in_entry_code(unsigned long ip)
  82 {
  83         char *addr = (char *)ip;
  84
  85         if (addr >= __entry_text_start && addr < __entry_text_end)
  86                 return true;
  87
  88         if (addr >= __irqentry_text_start && addr < __irqentry_text_end)
  89                 return true;
  90
  91         return false;
  92 }
  93
  94 static inline unsigned long *last_frame(struct unwind_state *state)
  95 {
  96         return (unsigned long *)task_pt_regs(state->task) - 2;
  97 }
  98
  99 static bool is_last_frame(struct unwind_state *state)
 100 {
 101         return state->bp == last_frame(state);
 102 }
 103
 104 #ifdef CONFIG_X86_32
 105 #define GCC_REALIGN_WORDS 3
 106 #else
 107 #define GCC_REALIGN_WORDS 1
 108 #endif
 109
 110 static inline unsigned long *last_aligned_frame(struct unwind_state *state)
 111 {
 112         return last_frame(state) - GCC_REALIGN_WORDS;
 113 }
 114
 115 static bool is_last_aligned_frame(struct unwind_state *state)
 116 {
 117         unsigned long *last_bp = last_frame(state);
 118         unsigned long *aligned_bp = last_aligned_frame(state);
 119
 120         /*
 121          * GCC can occasionally decide to realign the stack pointer and change
 122          * the offset of the stack frame in the prologue of a function called
 123          * by head/entry code.  Examples:
 124          *
 125          * <start_secondary>:
 126          *      push   %edi
 127          *      lea    0x8(%esp),%edi
 128          *      and    $0xfffffff8,%esp
 129          *      pushl  -0x4(%edi)
 130          *      push   %ebp
 131          *      mov    %esp,%ebp
 132          *
 133          * <x86_64_start_kernel>:
 134          *      lea    0x8(%rsp),%r10
 135          *      and    $0xfffffffffffffff0,%rsp
 136          *      pushq  -0x8(%r10)
 137          *      push   %rbp
 138          *      mov    %rsp,%rbp
 139          *
 140          * After aligning the stack, it pushes a duplicate copy of the return
 141          * address before pushing the frame pointer.
 142          */
 143         return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
 144 }
 145
 146 static bool is_last_ftrace_frame(struct unwind_state *state)
 147 {
 148         unsigned long *last_bp = last_frame(state);
 149         unsigned long *last_ftrace_bp = last_bp - 3;
 150
 151         /*
 152          * When unwinding from an ftrace handler of a function called by entry
 153          * code, the stack layout of the last frame is:
 154          *
 155          *   bp
 156          *   parent ret addr
 157          *   bp
 158          *   function ret addr
 159          *   parent ret addr
 160          *   pt_regs
 161          *   -----------------
 162          */
 163         return (state->bp == last_ftrace_bp &&
 164                 *state->bp == *(state->bp + 2) &&
 165                 *(state->bp + 1) == *(state->bp + 4));
 166 }
 167
 168 static bool is_last_task_frame(struct unwind_state *state)
 169 {
 170         return is_last_frame(state) || is_last_aligned_frame(state) ||
 171                is_last_ftrace_frame(state);
 172 }
 173
 174 /*
 175  * This determines if the frame pointer actually contains an encoded pointer to
 176  * pt_regs on the stack.  See ENCODE_FRAME_POINTER.
 177  */
 178 #ifdef CONFIG_X86_64
 179 static struct pt_regs *decode_frame_pointer(unsigned long *bp)
 180 {
 181         unsigned long regs = (unsigned long)bp;
 182
 183         if (!(regs & 0x1))
 184                 return NULL;
 185
 186         return (struct pt_regs *)(regs & ~0x1);
 187 }
 188 #else
 189 static struct pt_regs *decode_frame_pointer(unsigned long *bp)
 190 {
 191         unsigned long regs = (unsigned long)bp;
 192
 193         if (regs & 0x80000000)
 194                 return NULL;
 195
 196         return (struct pt_regs *)(regs | 0x80000000);
 197 }
 198 #endif
 199
 200 #ifdef CONFIG_X86_32
 201 #define KERNEL_REGS_SIZE (sizeof(struct pt_regs) - 2*sizeof(long))
 202 #else
 203 #define KERNEL_REGS_SIZE (sizeof(struct pt_regs))
 204 #endif
 205
 206 static bool update_stack_state(struct unwind_state *state,
 207                                unsigned long *next_bp)
 208 {
 209         struct stack_info *info = &state->stack_info;
 210         enum stack_type prev_type = info->type;
 211         struct pt_regs *regs;
 212         unsigned long *frame, *prev_frame_end, *addr_p, addr;
 213         size_t len;
 214
 215         if (state->regs)
 216                 prev_frame_end = (void *)state->regs + regs_size(state->regs);
 217         else
 218                 prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE;
 219
 220         /* Is the next frame pointer an encoded pointer to pt_regs? */
 221         regs = decode_frame_pointer(next_bp);
 222         if (regs) {
 223                 frame = (unsigned long *)regs;
 224                 len = KERNEL_REGS_SIZE;
 225                 state->got_irq = true;
 226         } else {
 227                 frame = next_bp;
 228                 len = FRAME_HEADER_SIZE;
 229         }
 230
 231         /*
 232          * If the next bp isn't on the current stack, switch to the next one.
 233          *
 234          * We may have to traverse multiple stacks to deal with the possibility
 235          * that info->next_sp could point to an empty stack and the next bp
 236          * could be on a subsequent stack.
 237          */
 238         while (!on_stack(info, frame, len))
 239                 if (get_stack_info(info->next_sp, state->task, info,
 240                                    &state->stack_mask))
 241                         return false;
 242
 243         /* Make sure it only unwinds up and doesn't overlap the prev frame: */
 244         if (state->orig_sp && state->stack_info.type == prev_type &&
 245             frame < prev_frame_end)
 246                 return false;
 247
 248         /*
 249          * On 32-bit with user mode regs, make sure the last two regs are safe
 250          * to access:
 251          */
 252         if (IS_ENABLED(CONFIG_X86_32) && regs && user_mode(regs) &&
 253             !on_stack(info, frame, len + 2*sizeof(long)))
 254                 return false;
 255
 256         /* Move state to the next frame: */
 257         if (regs) {
 258                 state->regs = regs;
 259                 state->bp = NULL;
 260         } else {
 261                 state->bp = next_bp;
 262                 state->regs = NULL;
 263         }
 264
 265         /* Save the return address: */
 266         if (state->regs && user_mode(state->regs))
 267                 state->ip = 0;
 268         else {
 269                 addr_p = unwind_get_return_address_ptr(state);
 270                 addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
 271                 state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
 272                                                   addr, addr_p);
 273         }
 274
 275         /* Save the original stack pointer for unwind_dump(): */
 276         if (!state->orig_sp)
 277                 state->orig_sp = frame;
 278
 279         return true;
 280 }
 281
 282 bool unwind_next_frame(struct unwind_state *state)
 283 {
 284         struct pt_regs *regs;
 285         unsigned long *next_bp;
 286
 287         if (unwind_done(state))
 288                 return false;
 289
 290         /* Have we reached the end? */
 291         if (state->regs && user_mode(state->regs))
 292                 goto the_end;
 293
 294         if (is_last_task_frame(state)) {
 295                 regs = task_pt_regs(state->task);
 296
 297                 /*
 298                  * kthreads (other than the boot CPU's idle thread) have some
 299                  * partial regs at the end of their stack which were placed
 300                  * there by copy_thread_tls().  But the regs don't have any
 301                  * useful information, so we can skip them.
 302                  *
 303                  * This user_mode() check is slightly broader than a PF_KTHREAD
 304                  * check because it also catches the awkward situation where a
 305                  * newly forked kthread transitions into a user task by calling
 306                  * do_execve(), which eventually clears PF_KTHREAD.
 307                  */
 308                 if (!user_mode(regs))
 309                         goto the_end;
 310
 311                 /*
 312                  * We're almost at the end, but not quite: there's still the
 313                  * syscall regs frame.  Entry code doesn't encode the regs
 314                  * pointer for syscalls, so we have to set it manually.
 315                  */
 316                 state->regs = regs;
 317                 state->bp = NULL;
 318                 state->ip = 0;
 319                 return true;
 320         }
 321
 322         /* Get the next frame pointer: */
 323         if (state->next_bp) {
 324                 next_bp = state->next_bp;
 325                 state->next_bp = NULL;
 326         } else if (state->regs) {
 327                 next_bp = (unsigned long *)state->regs->bp;
 328         } else {
 329                 next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);
 330         }
 331
 332         /* Move to the next frame if it's safe: */
 333         if (!update_stack_state(state, next_bp))
 334                 goto bad_address;
 335
 336         return true;
 337
 338 bad_address:
 339         state->error = true;
 340
 341         /*
 342          * When unwinding a non-current task, the task might actually be
 343          * running on another CPU, in which case it could be modifying its
 344          * stack while we're reading it.  This is generally not a problem and
 345          * can be ignored as long as the caller understands that unwinding
 346          * another task will not always succeed.
 347          */
 348         if (state->task != current)
 349                 goto the_end;
 350
 351         /*
 352          * Don't warn if the unwinder got lost due to an interrupt in entry
 353          * code or in the C handler before the first frame pointer got set up:
 354          */
 355         if (state->got_irq && in_entry_code(state->ip))
 356                 goto the_end;
 357         if (state->regs &&
 358             state->regs->sp >= (unsigned long)last_aligned_frame(state) &&
 359             state->regs->sp < (unsigned long)task_pt_regs(state->task))
 360                 goto the_end;
 361
 362         /*
 363          * There are some known frame pointer issues on 32-bit.  Disable
 364          * unwinder warnings on 32-bit until it gets objtool support.
 365          */
 366         if (IS_ENABLED(CONFIG_X86_32))
 367                 goto the_end;
 368
 369         if (state->regs) {
 370                 printk_deferred_once(KERN_WARNING
 371                         "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
 372                         state->regs, state->task->comm,
 373                         state->task->pid, next_bp);
 374                 unwind_dump(state);
 375         } else {
 376                 printk_deferred_once(KERN_WARNING
 377                         "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
 378                         state->bp, state->task->comm,
 379                         state->task->pid, next_bp);
 380                 unwind_dump(state);
 381         }
 382 the_end:
 383         state->stack_info.type = STACK_TYPE_UNKNOWN;
 384         return false;
 385 }
 386 EXPORT_SYMBOL_GPL(unwind_next_frame);
 387
 388 void __unwind_start(struct unwind_state *state, struct task_struct *task,
 389                     struct pt_regs *regs, unsigned long *first_frame)
 390 {
 391         unsigned long *bp;
 392
 393         memset(state, 0, sizeof(*state));
 394         state->task = task;
 395         state->got_irq = (regs);
 396
 397         /* Don't even attempt to start from user mode regs: */
 398         if (regs && user_mode(regs)) {
 399                 state->stack_info.type = STACK_TYPE_UNKNOWN;
 400                 return;
 401         }
 402
 403         bp = get_frame_pointer(task, regs);
 404
 405         /*
 406          * If we crash with IP==0, the last successfully executed instruction
 407          * was probably an indirect function call with a NULL function pointer.
 408          * That means that SP points into the middle of an incomplete frame:
 409          * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we
 410          * would have written a frame pointer if we hadn't crashed.
 411          * Pretend that the frame is complete and that BP points to it, but save
 412          * the real BP so that we can use it when looking for the next frame.
 413          */
 414         if (regs && regs->ip == 0 &&
 415             (unsigned long *)kernel_stack_pointer(regs) >= first_frame) {
 416                 state->next_bp = bp;
 417                 bp = ((unsigned long *)kernel_stack_pointer(regs)) - 1;
 418         }
 419
 420         /* Initialize stack info and make sure the frame data is accessible: */
 421         get_stack_info(bp, state->task, &state->stack_info,
 422                        &state->stack_mask);
 423         update_stack_state(state, bp);
 424
 425         /*
 426          * The caller can provide the address of the first frame directly
 427          * (first_frame) or indirectly (regs->sp) to indicate which stack frame
 428          * to start unwinding at.  Skip ahead until we reach it.
 429          */
 430         while (!unwind_done(state) &&
 431                (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
 432                         (state->next_bp == NULL && state->bp < first_frame)))
 433                 unwind_next_frame(state);
 434 }
 435 EXPORT_SYMBOL_GPL(__unwind_start);