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