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 /* 187 * While walking the stack, KMSAN may stomp on stale locals from other 188 * functions that were marked as uninitialized upon function exit, and 189 * now hold the call frame information for the current function (e.g. the frame 190 * pointer). Because KMSAN does not specifically mark call frames as 191 * initialized, false positive reports are possible. To prevent such reports, 192 * we mark the functions scanning the stack (here and below) with 193 * __no_kmsan_checks. 194 */ 195 __no_kmsan_checks 196 static bool update_stack_state(struct unwind_state *state, 197 unsigned long *next_bp) 198 { 199 struct stack_info *info = &state->stack_info; 200 enum stack_type prev_type = info->type; 201 struct pt_regs *regs; 202 unsigned long *frame, *prev_frame_end, *addr_p, addr; 203 size_t len; 204 205 if (state->regs) 206 prev_frame_end = (void *)state->regs + sizeof(*state->regs); 207 else 208 prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE; 209 210 /* Is the next frame pointer an encoded pointer to pt_regs? */ 211 regs = decode_frame_pointer(next_bp); 212 if (regs) { 213 frame = (unsigned long *)regs; 214 len = sizeof(*regs); 215 state->got_irq = true; 216 } else { 217 frame = next_bp; 218 len = FRAME_HEADER_SIZE; 219 } 220 221 /* 222 * If the next bp isn't on the current stack, switch to the next one. 223 * 224 * We may have to traverse multiple stacks to deal with the possibility 225 * that info->next_sp could point to an empty stack and the next bp 226 * could be on a subsequent stack. 227 */ 228 while (!on_stack(info, frame, len)) 229 if (get_stack_info(info->next_sp, state->task, info, 230 &state->stack_mask)) 231 return false; 232 233 /* Make sure it only unwinds up and doesn't overlap the prev frame: */ 234 if (state->orig_sp && state->stack_info.type == prev_type && 235 frame < prev_frame_end) 236 return false; 237 238 /* Move state to the next frame: */ 239 if (regs) { 240 state->regs = regs; 241 state->bp = NULL; 242 } else { 243 state->bp = next_bp; 244 state->regs = NULL; 245 } 246 247 /* Save the return address: */ 248 if (state->regs && user_mode(state->regs)) 249 state->ip = 0; 250 else { 251 addr_p = unwind_get_return_address_ptr(state); 252 addr = READ_ONCE_TASK_STACK(state->task, *addr_p); 253 state->ip = unwind_recover_ret_addr(state, addr, addr_p); 254 } 255 256 /* Save the original stack pointer for unwind_dump(): */ 257 if (!state->orig_sp) 258 state->orig_sp = frame; 259 260 return true; 261 } 262 263 __no_kmsan_checks 264 bool unwind_next_frame(struct unwind_state *state) 265 { 266 struct pt_regs *regs; 267 unsigned long *next_bp; 268 269 if (unwind_done(state)) 270 return false; 271 272 /* Have we reached the end? */ 273 if (state->regs && user_mode(state->regs)) 274 goto the_end; 275 276 if (is_last_task_frame(state)) { 277 regs = task_pt_regs(state->task); 278 279 /* 280 * kthreads (other than the boot CPU's idle thread) have some 281 * partial regs at the end of their stack which were placed 282 * there by copy_thread(). But the regs don't have any 283 * useful information, so we can skip them. 284 * 285 * This user_mode() check is slightly broader than a PF_KTHREAD 286 * check because it also catches the awkward situation where a 287 * newly forked kthread transitions into a user task by calling 288 * kernel_execve(), which eventually clears PF_KTHREAD. 289 */ 290 if (!user_mode(regs)) 291 goto the_end; 292 293 /* 294 * We're almost at the end, but not quite: there's still the 295 * syscall regs frame. Entry code doesn't encode the regs 296 * pointer for syscalls, so we have to set it manually. 297 */ 298 state->regs = regs; 299 state->bp = NULL; 300 state->ip = 0; 301 return true; 302 } 303 304 /* Get the next frame pointer: */ 305 if (state->next_bp) { 306 next_bp = state->next_bp; 307 state->next_bp = NULL; 308 } else if (state->regs) { 309 next_bp = (unsigned long *)state->regs->bp; 310 } else { 311 next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp); 312 } 313 314 /* Move to the next frame if it's safe: */ 315 if (!update_stack_state(state, next_bp)) 316 goto bad_address; 317 318 return true; 319 320 bad_address: 321 state->error = true; 322 323 /* 324 * When unwinding a non-current task, the task might actually be 325 * running on another CPU, in which case it could be modifying its 326 * stack while we're reading it. This is generally not a problem and 327 * can be ignored as long as the caller understands that unwinding 328 * another task will not always succeed. 329 */ 330 if (state->task != current) 331 goto the_end; 332 333 /* 334 * Don't warn if the unwinder got lost due to an interrupt in entry 335 * code or in the C handler before the first frame pointer got set up: 336 */ 337 if (state->got_irq && in_entry_code(state->ip)) 338 goto the_end; 339 if (state->regs && 340 state->regs->sp >= (unsigned long)last_aligned_frame(state) && 341 state->regs->sp < (unsigned long)task_pt_regs(state->task)) 342 goto the_end; 343 344 /* 345 * There are some known frame pointer issues on 32-bit. Disable 346 * unwinder warnings on 32-bit until it gets objtool support. 347 */ 348 if (IS_ENABLED(CONFIG_X86_32)) 349 goto the_end; 350 351 if (state->task != current) 352 goto the_end; 353 354 if (state->regs) { 355 printk_deferred_once(KERN_WARNING 356 "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n", 357 state->regs, state->task->comm, 358 state->task->pid, next_bp); 359 unwind_dump(state); 360 } else { 361 printk_deferred_once(KERN_WARNING 362 "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n", 363 state->bp, state->task->comm, 364 state->task->pid, next_bp); 365 unwind_dump(state); 366 } 367 the_end: 368 state->stack_info.type = STACK_TYPE_UNKNOWN; 369 return false; 370 } 371 EXPORT_SYMBOL_GPL(unwind_next_frame); 372 373 void __unwind_start(struct unwind_state *state, struct task_struct *task, 374 struct pt_regs *regs, unsigned long *first_frame) 375 { 376 unsigned long *bp; 377 378 memset(state, 0, sizeof(*state)); 379 state->task = task; 380 state->got_irq = (regs); 381 382 /* Don't even attempt to start from user mode regs: */ 383 if (regs && user_mode(regs)) { 384 state->stack_info.type = STACK_TYPE_UNKNOWN; 385 return; 386 } 387 388 bp = get_frame_pointer(task, regs); 389 390 /* 391 * If we crash with IP==0, the last successfully executed instruction 392 * was probably an indirect function call with a NULL function pointer. 393 * That means that SP points into the middle of an incomplete frame: 394 * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we 395 * would have written a frame pointer if we hadn't crashed. 396 * Pretend that the frame is complete and that BP points to it, but save 397 * the real BP so that we can use it when looking for the next frame. 398 */ 399 if (regs && regs->ip == 0 && (unsigned long *)regs->sp >= first_frame) { 400 state->next_bp = bp; 401 bp = ((unsigned long *)regs->sp) - 1; 402 } 403 404 /* Initialize stack info and make sure the frame data is accessible: */ 405 get_stack_info(bp, state->task, &state->stack_info, 406 &state->stack_mask); 407 update_stack_state(state, bp); 408 409 /* 410 * The caller can provide the address of the first frame directly 411 * (first_frame) or indirectly (regs->sp) to indicate which stack frame 412 * to start unwinding at. Skip ahead until we reach it. 413 */ 414 while (!unwind_done(state) && 415 (!on_stack(&state->stack_info, first_frame, sizeof(long)) || 416 (state->next_bp == NULL && state->bp < first_frame))) 417 unwind_next_frame(state); 418 } 419 EXPORT_SYMBOL_GPL(__unwind_start); 420