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 /* 14 * This disables KASAN checking when reading a value from another task's stack, 15 * since the other task could be running on another CPU and could have poisoned 16 * the stack in the meantime. 17 */ 18 #define READ_ONCE_TASK_STACK(task, x) \ 19 ({ \ 20 unsigned long val; \ 21 if (task == current) \ 22 val = READ_ONCE(x); \ 23 else \ 24 val = READ_ONCE_NOCHECK(x); \ 25 val; \ 26 }) 27 28 static void unwind_dump(struct unwind_state *state) 29 { 30 static bool dumped_before = false; 31 bool prev_zero, zero = false; 32 unsigned long word, *sp; 33 struct stack_info stack_info = {0}; 34 unsigned long visit_mask = 0; 35 36 if (dumped_before) 37 return; 38 39 dumped_before = true; 40 41 printk_deferred("unwind stack type:%d next_sp:%p mask:0x%lx graph_idx:%d\n", 42 state->stack_info.type, state->stack_info.next_sp, 43 state->stack_mask, state->graph_idx); 44 45 for (sp = state->orig_sp; sp; sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) { 46 if (get_stack_info(sp, state->task, &stack_info, &visit_mask)) 47 break; 48 49 for (; sp < stack_info.end; sp++) { 50 51 word = READ_ONCE_NOCHECK(*sp); 52 53 prev_zero = zero; 54 zero = word == 0; 55 56 if (zero) { 57 if (!prev_zero) 58 printk_deferred("%p: %0*x ...\n", 59 sp, BITS_PER_LONG/4, 0); 60 continue; 61 } 62 63 printk_deferred("%p: %0*lx (%pB)\n", 64 sp, BITS_PER_LONG/4, word, (void *)word); 65 } 66 } 67 } 68 69 unsigned long unwind_get_return_address(struct unwind_state *state) 70 { 71 if (unwind_done(state)) 72 return 0; 73 74 return __kernel_text_address(state->ip) ? state->ip : 0; 75 } 76 EXPORT_SYMBOL_GPL(unwind_get_return_address); 77 78 static size_t regs_size(struct pt_regs *regs) 79 { 80 /* x86_32 regs from kernel mode are two words shorter: */ 81 if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs)) 82 return sizeof(*regs) - 2*sizeof(long); 83 84 return sizeof(*regs); 85 } 86 87 static bool in_entry_code(unsigned long ip) 88 { 89 char *addr = (char *)ip; 90 91 if (addr >= __entry_text_start && addr < __entry_text_end) 92 return true; 93 94 #if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) 95 if (addr >= __irqentry_text_start && addr < __irqentry_text_end) 96 return true; 97 #endif 98 99 return false; 100 } 101 102 static inline unsigned long *last_frame(struct unwind_state *state) 103 { 104 return (unsigned long *)task_pt_regs(state->task) - 2; 105 } 106 107 static bool is_last_frame(struct unwind_state *state) 108 { 109 return state->bp == last_frame(state); 110 } 111 112 #ifdef CONFIG_X86_32 113 #define GCC_REALIGN_WORDS 3 114 #else 115 #define GCC_REALIGN_WORDS 1 116 #endif 117 118 static inline unsigned long *last_aligned_frame(struct unwind_state *state) 119 { 120 return last_frame(state) - GCC_REALIGN_WORDS; 121 } 122 123 static bool is_last_aligned_frame(struct unwind_state *state) 124 { 125 unsigned long *last_bp = last_frame(state); 126 unsigned long *aligned_bp = last_aligned_frame(state); 127 128 /* 129 * GCC can occasionally decide to realign the stack pointer and change 130 * the offset of the stack frame in the prologue of a function called 131 * by head/entry code. Examples: 132 * 133 * <start_secondary>: 134 * push %edi 135 * lea 0x8(%esp),%edi 136 * and $0xfffffff8,%esp 137 * pushl -0x4(%edi) 138 * push %ebp 139 * mov %esp,%ebp 140 * 141 * <x86_64_start_kernel>: 142 * lea 0x8(%rsp),%r10 143 * and $0xfffffffffffffff0,%rsp 144 * pushq -0x8(%r10) 145 * push %rbp 146 * mov %rsp,%rbp 147 * 148 * After aligning the stack, it pushes a duplicate copy of the return 149 * address before pushing the frame pointer. 150 */ 151 return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1)); 152 } 153 154 static bool is_last_ftrace_frame(struct unwind_state *state) 155 { 156 unsigned long *last_bp = last_frame(state); 157 unsigned long *last_ftrace_bp = last_bp - 3; 158 159 /* 160 * When unwinding from an ftrace handler of a function called by entry 161 * code, the stack layout of the last frame is: 162 * 163 * bp 164 * parent ret addr 165 * bp 166 * function ret addr 167 * parent ret addr 168 * pt_regs 169 * ----------------- 170 */ 171 return (state->bp == last_ftrace_bp && 172 *state->bp == *(state->bp + 2) && 173 *(state->bp + 1) == *(state->bp + 4)); 174 } 175 176 static bool is_last_task_frame(struct unwind_state *state) 177 { 178 return is_last_frame(state) || is_last_aligned_frame(state) || 179 is_last_ftrace_frame(state); 180 } 181 182 /* 183 * This determines if the frame pointer actually contains an encoded pointer to 184 * pt_regs on the stack. See ENCODE_FRAME_POINTER. 185 */ 186 static struct pt_regs *decode_frame_pointer(unsigned long *bp) 187 { 188 unsigned long regs = (unsigned long)bp; 189 190 if (!(regs & 0x1)) 191 return NULL; 192 193 return (struct pt_regs *)(regs & ~0x1); 194 } 195 196 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 + regs_size(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 = regs_size(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 = ftrace_graph_ret_addr(state->task, &state->graph_idx, 254 addr, addr_p); 255 } 256 257 /* Save the original stack pointer for unwind_dump(): */ 258 if (!state->orig_sp) 259 state->orig_sp = frame; 260 261 return true; 262 } 263 264 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_tls(). 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 * do_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->regs) 306 next_bp = (unsigned long *)state->regs->bp; 307 else 308 next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp); 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 if (state->regs) { 341 printk_deferred_once(KERN_WARNING 342 "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n", 343 state->regs, state->task->comm, 344 state->task->pid, next_bp); 345 unwind_dump(state); 346 } else { 347 printk_deferred_once(KERN_WARNING 348 "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n", 349 state->bp, state->task->comm, 350 state->task->pid, next_bp); 351 unwind_dump(state); 352 } 353 the_end: 354 state->stack_info.type = STACK_TYPE_UNKNOWN; 355 return false; 356 } 357 EXPORT_SYMBOL_GPL(unwind_next_frame); 358 359 void __unwind_start(struct unwind_state *state, struct task_struct *task, 360 struct pt_regs *regs, unsigned long *first_frame) 361 { 362 unsigned long *bp; 363 364 memset(state, 0, sizeof(*state)); 365 state->task = task; 366 state->got_irq = (regs); 367 368 /* Don't even attempt to start from user mode regs: */ 369 if (regs && user_mode(regs)) { 370 state->stack_info.type = STACK_TYPE_UNKNOWN; 371 return; 372 } 373 374 bp = get_frame_pointer(task, regs); 375 376 /* Initialize stack info and make sure the frame data is accessible: */ 377 get_stack_info(bp, state->task, &state->stack_info, 378 &state->stack_mask); 379 update_stack_state(state, bp); 380 381 /* 382 * The caller can provide the address of the first frame directly 383 * (first_frame) or indirectly (regs->sp) to indicate which stack frame 384 * to start unwinding at. Skip ahead until we reach it. 385 */ 386 while (!unwind_done(state) && 387 (!on_stack(&state->stack_info, first_frame, sizeof(long)) || 388 state->bp < first_frame)) 389 unwind_next_frame(state); 390 } 391 EXPORT_SYMBOL_GPL(__unwind_start); 392