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