arch/x86/kernel/unwind_frame.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/sched.h>
   3 #include <linux/sched/task.h>
   4 #include <linux/sched/task_stack.h>
   5 #include <linux/interrupt.h>
   6 #include <asm/sections.h>
   7 #include <asm/ptrace.h>
   8 #include <asm/bitops.h>
   9 #include <asm/stacktrace.h>
  10 #include <asm/unwind.h>
  11
  12 #define FRAME_HEADER_SIZE (sizeof(long) * 2)
  13
  14 unsigned long unwind_get_return_address(struct unwind_state *state)
  15 {
  16         if (unwind_done(state))
  17                 return 0;
  18
  19         return __kernel_text_address(state->ip) ? state->ip : 0;
  20 }
  21 EXPORT_SYMBOL_GPL(unwind_get_return_address);
  22
  23 unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
  24 {
  25         if (unwind_done(state))
  26                 return NULL;
  27
  28         return state->regs ? &state->regs->ip : state->bp + 1;
  29 }
  30
  31 static void unwind_dump(struct unwind_state *state)
  32 {
  33         static bool dumped_before = false;
  34         bool prev_zero, zero = false;
  35         unsigned long word, *sp;
  36         struct stack_info stack_info = {0};
  37         unsigned long visit_mask = 0;
  38
  39         if (dumped_before)
  40                 return;
  41
  42         dumped_before = true;
  43
  44         printk_deferred("unwind stack type:%d next_sp:%p mask:0x%lx graph_idx:%d\n",
  45                         state->stack_info.type, state->stack_info.next_sp,
  46                         state->stack_mask, state->graph_idx);
  47
  48         for (sp = PTR_ALIGN(state->orig_sp, sizeof(long)); sp;
  49              sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
  50                 if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
  51                         break;
  52
  53                 for (; sp < stack_info.end; sp++) {
  54
  55                         word = READ_ONCE_NOCHECK(*sp);
  56
  57                         prev_zero = zero;
  58                         zero = word == 0;
  59
  60                         if (zero) {
  61                                 if (!prev_zero)
  62                                         printk_deferred("%p: %0*x ...\n",
  63                                                         sp, BITS_PER_LONG/4, 0);
  64                                 continue;
  65                         }
  66
  67                         printk_deferred("%p: %0*lx (%pB)\n",
  68                                         sp, BITS_PER_LONG/4, word, (void *)word);
  69                 }
  70         }
  71 }
  72
  73 static bool in_entry_code(unsigned long ip)
  74 {
  75         char *addr = (char *)ip;
  76
  77         return addr >= __entry_text_start && addr < __entry_text_end;
  78 }
  79
  80 static inline unsigned long *last_frame(struct unwind_state *state)
  81 {
  82         return (unsigned long *)task_pt_regs(state->task) - 2;
  83 }
  84
  85 static bool is_last_frame(struct unwind_state *state)
  86 {
  87         return state->bp == last_frame(state);
  88 }
  89
  90 #ifdef CONFIG_X86_32
  91 #define GCC_REALIGN_WORDS 3
  92 #else
  93 #define GCC_REALIGN_WORDS 1
  94 #endif
  95
  96 static inline unsigned long *last_aligned_frame(struct unwind_state *state)
  97 {
  98         return last_frame(state) - GCC_REALIGN_WORDS;
  99 }
 100
 101 static bool is_last_aligned_frame(struct unwind_state *state)
 102 {
 103         unsigned long *last_bp = last_frame(state);
 104         unsigned long *aligned_bp = last_aligned_frame(state);
 105
 106         /*
 107          * GCC can occasionally decide to realign the stack pointer and change
 108          * the offset of the stack frame in the prologue of a function called
 109          * by head/entry code.  Examples:
 110          *
 111          * <start_secondary>:
 112          *      push   %edi
 113          *      lea    0x8(%esp),%edi
 114          *      and    $0xfffffff8,%esp
 115          *      pushl  -0x4(%edi)
 116          *      push   %ebp
 117          *      mov    %esp,%ebp
 118          *
 119          * <x86_64_start_kernel>:
 120          *      lea    0x8(%rsp),%r10
 121          *      and    $0xfffffffffffffff0,%rsp
 122          *      pushq  -0x8(%r10)
 123          *      push   %rbp
 124          *      mov    %rsp,%rbp
 125          *
 126          * After aligning the stack, it pushes a duplicate copy of the return
 127          * address before pushing the frame pointer.
 128          */
 129         return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
 130 }
 131
 132 static bool is_last_ftrace_frame(struct unwind_state *state)
 133 {
 134         unsigned long *last_bp = last_frame(state);
 135         unsigned long *last_ftrace_bp = last_bp - 3;
 136
 137         /*
 138          * When unwinding from an ftrace handler of a function called by entry
 139          * code, the stack layout of the last frame is:
 140          *
 141          *   bp
 142          *   parent ret addr
 143          *   bp
 144          *   function ret addr
 145          *   parent ret addr
 146          *   pt_regs
 147          *   -----------------
 148          */
 149         return (state->bp == last_ftrace_bp &&
 150                 *state->bp == *(state->bp + 2) &&
 151                 *(state->bp + 1) == *(state->bp + 4));
 152 }
 153
 154 static bool is_last_task_frame(struct unwind_state *state)
 155 {
 156         return is_last_frame(state) || is_last_aligned_frame(state) ||
 157                is_last_ftrace_frame(state);
 158 }
 159
 160 /*
 161  * This determines if the frame pointer actually contains an encoded pointer to
 162  * pt_regs on the stack.  See ENCODE_FRAME_POINTER.
 163  */
 164 #ifdef CONFIG_X86_64
 165 static struct pt_regs *decode_frame_pointer(unsigned long *bp)
 166 {
 167         unsigned long regs = (unsigned long)bp;
 168
 169         if (!(regs & 0x1))
 170                 return NULL;
 171
 172         return (struct pt_regs *)(regs & ~0x1);
 173 }
 174 #else
 175 static struct pt_regs *decode_frame_pointer(unsigned long *bp)
 176 {
 177         unsigned long regs = (unsigned long)bp;
 178
 179         if (regs & 0x80000000)
 180                 return NULL;
 181
 182         return (struct pt_regs *)(regs | 0x80000000);
 183 }
 184 #endif
 185
 186 static bool update_stack_state(struct unwind_state *state,
 187                                unsigned long *next_bp)
 188 {
 189         struct stack_info *info = &state->stack_info;
 190         enum stack_type prev_type = info->type;
 191         struct pt_regs *regs;
 192         unsigned long *frame, *prev_frame_end, *addr_p, addr;
 193         size_t len;
 194
 195         if (state->regs)
 196                 prev_frame_end = (void *)state->regs + sizeof(*state->regs);
 197         else
 198                 prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE;
 199
 200         /* Is the next frame pointer an encoded pointer to pt_regs? */
 201         regs = decode_frame_pointer(next_bp);
 202         if (regs) {
 203                 frame = (unsigned long *)regs;
 204                 len = sizeof(*regs);
 205                 state->got_irq = true;
 206         } else {
 207                 frame = next_bp;
 208                 len = FRAME_HEADER_SIZE;
 209         }
 210
 211         /*
 212          * If the next bp isn't on the current stack, switch to the next one.
 213          *
 214          * We may have to traverse multiple stacks to deal with the possibility
 215          * that info->next_sp could point to an empty stack and the next bp
 216          * could be on a subsequent stack.
 217          */
 218         while (!on_stack(info, frame, len))
 219                 if (get_stack_info(info->next_sp, state->task, info,
 220                                    &state->stack_mask))
 221                         return false;
 222
 223         /* Make sure it only unwinds up and doesn't overlap the prev frame: */
 224         if (state->orig_sp && state->stack_info.type == prev_type &&
 225             frame < prev_frame_end)
 226                 return false;
 227
 228         /* Move state to the next frame: */
 229         if (regs) {
 230                 state->regs = regs;
 231                 state->bp = NULL;
 232         } else {
 233                 state->bp = next_bp;
 234                 state->regs = NULL;
 235         }
 236
 237         /* Save the return address: */
 238         if (state->regs && user_mode(state->regs))
 239                 state->ip = 0;
 240         else {
 241                 addr_p = unwind_get_return_address_ptr(state);
 242                 addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
 243                 state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
 244                                                   addr, addr_p);
 245         }
 246
 247         /* Save the original stack pointer for unwind_dump(): */
 248         if (!state->orig_sp)
 249                 state->orig_sp = frame;
 250
 251         return true;
 252 }
 253
 254 bool unwind_next_frame(struct unwind_state *state)
 255 {
 256         struct pt_regs *regs;
 257         unsigned long *next_bp;
 258
 259         if (unwind_done(state))
 260                 return false;
 261
 262         /* Have we reached the end? */
 263         if (state->regs && user_mode(state->regs))
 264                 goto the_end;
 265
 266         if (is_last_task_frame(state)) {
 267                 regs = task_pt_regs(state->task);
 268
 269                 /*
 270                  * kthreads (other than the boot CPU's idle thread) have some
 271                  * partial regs at the end of their stack which were placed
 272                  * there by copy_thread().  But the regs don't have any
 273                  * useful information, so we can skip them.
 274                  *
 275                  * This user_mode() check is slightly broader than a PF_KTHREAD
 276                  * check because it also catches the awkward situation where a
 277                  * newly forked kthread transitions into a user task by calling
 278                  * kernel_execve(), which eventually clears PF_KTHREAD.
 279                  */
 280                 if (!user_mode(regs))
 281                         goto the_end;
 282
 283                 /*
 284                  * We're almost at the end, but not quite: there's still the
 285                  * syscall regs frame.  Entry code doesn't encode the regs
 286                  * pointer for syscalls, so we have to set it manually.
 287                  */
 288                 state->regs = regs;
 289                 state->bp = NULL;
 290                 state->ip = 0;
 291                 return true;
 292         }
 293
 294         /* Get the next frame pointer: */
 295         if (state->next_bp) {
 296                 next_bp = state->next_bp;
 297                 state->next_bp = NULL;
 298         } else if (state->regs) {
 299                 next_bp = (unsigned long *)state->regs->bp;
 300         } else {
 301                 next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);
 302         }
 303
 304         /* Move to the next frame if it's safe: */
 305         if (!update_stack_state(state, next_bp))
 306                 goto bad_address;
 307
 308         return true;
 309
 310 bad_address:
 311         state->error = true;
 312
 313         /*
 314          * When unwinding a non-current task, the task might actually be
 315          * running on another CPU, in which case it could be modifying its
 316          * stack while we're reading it.  This is generally not a problem and
 317          * can be ignored as long as the caller understands that unwinding
 318          * another task will not always succeed.
 319          */
 320         if (state->task != current)
 321                 goto the_end;
 322
 323         /*
 324          * Don't warn if the unwinder got lost due to an interrupt in entry
 325          * code or in the C handler before the first frame pointer got set up:
 326          */
 327         if (state->got_irq && in_entry_code(state->ip))
 328                 goto the_end;
 329         if (state->regs &&
 330             state->regs->sp >= (unsigned long)last_aligned_frame(state) &&
 331             state->regs->sp < (unsigned long)task_pt_regs(state->task))
 332                 goto the_end;
 333
 334         /*
 335          * There are some known frame pointer issues on 32-bit.  Disable
 336          * unwinder warnings on 32-bit until it gets objtool support.
 337          */
 338         if (IS_ENABLED(CONFIG_X86_32))
 339                 goto the_end;
 340
 341         if (state->task != current)
 342                 goto the_end;
 343
 344         if (state->regs) {
 345                 printk_deferred_once(KERN_WARNING
 346                         "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
 347                         state->regs, state->task->comm,
 348                         state->task->pid, next_bp);
 349                 unwind_dump(state);
 350         } else {
 351                 printk_deferred_once(KERN_WARNING
 352                         "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
 353                         state->bp, state->task->comm,
 354                         state->task->pid, next_bp);
 355                 unwind_dump(state);
 356         }
 357 the_end:
 358         state->stack_info.type = STACK_TYPE_UNKNOWN;
 359         return false;
 360 }
 361 EXPORT_SYMBOL_GPL(unwind_next_frame);
 362
 363 void __unwind_start(struct unwind_state *state, struct task_struct *task,
 364                     struct pt_regs *regs, unsigned long *first_frame)
 365 {
 366         unsigned long *bp;
 367
 368         memset(state, 0, sizeof(*state));
 369         state->task = task;
 370         state->got_irq = (regs);
 371
 372         /* Don't even attempt to start from user mode regs: */
 373         if (regs && user_mode(regs)) {
 374                 state->stack_info.type = STACK_TYPE_UNKNOWN;
 375                 return;
 376         }
 377
 378         bp = get_frame_pointer(task, regs);
 379
 380         /*
 381          * If we crash with IP==0, the last successfully executed instruction
 382          * was probably an indirect function call with a NULL function pointer.
 383          * That means that SP points into the middle of an incomplete frame:
 384          * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we
 385          * would have written a frame pointer if we hadn't crashed.
 386          * Pretend that the frame is complete and that BP points to it, but save
 387          * the real BP so that we can use it when looking for the next frame.
 388          */
 389         if (regs && regs->ip == 0 && (unsigned long *)regs->sp >= first_frame) {
 390                 state->next_bp = bp;
 391                 bp = ((unsigned long *)regs->sp) - 1;
 392         }
 393
 394         /* Initialize stack info and make sure the frame data is accessible: */
 395         get_stack_info(bp, state->task, &state->stack_info,
 396                        &state->stack_mask);
 397         update_stack_state(state, bp);
 398
 399         /*
 400          * The caller can provide the address of the first frame directly
 401          * (first_frame) or indirectly (regs->sp) to indicate which stack frame
 402          * to start unwinding at.  Skip ahead until we reach it.
 403          */
 404         while (!unwind_done(state) &&
 405                (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
 406                         (state->next_bp == NULL && state->bp < first_frame)))
 407                 unwind_next_frame(state);
 408 }
 409 EXPORT_SYMBOL_GPL(__unwind_start);