1 #include <linux/sched.h> 2 #include <asm/ptrace.h> 3 #include <asm/bitops.h> 4 #include <asm/stacktrace.h> 5 #include <asm/unwind.h> 6 7 #define FRAME_HEADER_SIZE (sizeof(long) * 2) 8 9 /* 10 * This disables KASAN checking when reading a value from another task's stack, 11 * since the other task could be running on another CPU and could have poisoned 12 * the stack in the meantime. 13 */ 14 #define READ_ONCE_TASK_STACK(task, x) \ 15 ({ \ 16 unsigned long val; \ 17 if (task == current) \ 18 val = READ_ONCE(x); \ 19 else \ 20 val = READ_ONCE_NOCHECK(x); \ 21 val; \ 22 }) 23 24 static void unwind_dump(struct unwind_state *state, unsigned long *sp) 25 { 26 static bool dumped_before = false; 27 bool prev_zero, zero = false; 28 unsigned long word; 29 30 if (dumped_before) 31 return; 32 33 dumped_before = true; 34 35 printk_deferred("unwind stack type:%d next_sp:%p mask:%lx graph_idx:%d\n", 36 state->stack_info.type, state->stack_info.next_sp, 37 state->stack_mask, state->graph_idx); 38 39 for (sp = state->orig_sp; sp < state->stack_info.end; sp++) { 40 word = READ_ONCE_NOCHECK(*sp); 41 42 prev_zero = zero; 43 zero = word == 0; 44 45 if (zero) { 46 if (!prev_zero) 47 printk_deferred("%p: %016x ...\n", sp, 0); 48 continue; 49 } 50 51 printk_deferred("%p: %016lx (%pB)\n", sp, word, (void *)word); 52 } 53 } 54 55 unsigned long unwind_get_return_address(struct unwind_state *state) 56 { 57 unsigned long addr; 58 unsigned long *addr_p = unwind_get_return_address_ptr(state); 59 60 if (unwind_done(state)) 61 return 0; 62 63 if (state->regs && user_mode(state->regs)) 64 return 0; 65 66 addr = READ_ONCE_TASK_STACK(state->task, *addr_p); 67 addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, addr, 68 addr_p); 69 70 return __kernel_text_address(addr) ? addr : 0; 71 } 72 EXPORT_SYMBOL_GPL(unwind_get_return_address); 73 74 static size_t regs_size(struct pt_regs *regs) 75 { 76 /* x86_32 regs from kernel mode are two words shorter: */ 77 if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs)) 78 return sizeof(*regs) - 2*sizeof(long); 79 80 return sizeof(*regs); 81 } 82 83 static bool is_last_task_frame(struct unwind_state *state) 84 { 85 unsigned long bp = (unsigned long)state->bp; 86 unsigned long regs = (unsigned long)task_pt_regs(state->task); 87 88 /* 89 * We have to check for the last task frame at two different locations 90 * because gcc can occasionally decide to realign the stack pointer and 91 * change the offset of the stack frame by a word in the prologue of a 92 * function called by head/entry code. 93 */ 94 return bp == regs - FRAME_HEADER_SIZE || 95 bp == regs - FRAME_HEADER_SIZE - sizeof(long); 96 } 97 98 /* 99 * This determines if the frame pointer actually contains an encoded pointer to 100 * pt_regs on the stack. See ENCODE_FRAME_POINTER. 101 */ 102 static struct pt_regs *decode_frame_pointer(unsigned long *bp) 103 { 104 unsigned long regs = (unsigned long)bp; 105 106 if (!(regs & 0x1)) 107 return NULL; 108 109 return (struct pt_regs *)(regs & ~0x1); 110 } 111 112 static bool update_stack_state(struct unwind_state *state, void *addr, 113 size_t len) 114 { 115 struct stack_info *info = &state->stack_info; 116 enum stack_type orig_type = info->type; 117 118 /* 119 * If addr isn't on the current stack, switch to the next one. 120 * 121 * We may have to traverse multiple stacks to deal with the possibility 122 * that 'info->next_sp' could point to an empty stack and 'addr' could 123 * be on a subsequent stack. 124 */ 125 while (!on_stack(info, addr, len)) 126 if (get_stack_info(info->next_sp, state->task, info, 127 &state->stack_mask)) 128 return false; 129 130 if (!state->orig_sp || info->type != orig_type) 131 state->orig_sp = addr; 132 133 return true; 134 } 135 136 bool unwind_next_frame(struct unwind_state *state) 137 { 138 struct pt_regs *regs; 139 unsigned long *next_bp, *next_frame; 140 size_t next_len; 141 enum stack_type prev_type = state->stack_info.type; 142 143 if (unwind_done(state)) 144 return false; 145 146 /* have we reached the end? */ 147 if (state->regs && user_mode(state->regs)) 148 goto the_end; 149 150 if (is_last_task_frame(state)) { 151 regs = task_pt_regs(state->task); 152 153 /* 154 * kthreads (other than the boot CPU's idle thread) have some 155 * partial regs at the end of their stack which were placed 156 * there by copy_thread_tls(). But the regs don't have any 157 * useful information, so we can skip them. 158 * 159 * This user_mode() check is slightly broader than a PF_KTHREAD 160 * check because it also catches the awkward situation where a 161 * newly forked kthread transitions into a user task by calling 162 * do_execve(), which eventually clears PF_KTHREAD. 163 */ 164 if (!user_mode(regs)) 165 goto the_end; 166 167 /* 168 * We're almost at the end, but not quite: there's still the 169 * syscall regs frame. Entry code doesn't encode the regs 170 * pointer for syscalls, so we have to set it manually. 171 */ 172 state->regs = regs; 173 state->bp = NULL; 174 return true; 175 } 176 177 /* get the next frame pointer */ 178 if (state->regs) 179 next_bp = (unsigned long *)state->regs->bp; 180 else 181 next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task,*state->bp); 182 183 /* is the next frame pointer an encoded pointer to pt_regs? */ 184 regs = decode_frame_pointer(next_bp); 185 if (regs) { 186 next_frame = (unsigned long *)regs; 187 next_len = sizeof(*regs); 188 } else { 189 next_frame = next_bp; 190 next_len = FRAME_HEADER_SIZE; 191 } 192 193 /* make sure the next frame's data is accessible */ 194 if (!update_stack_state(state, next_frame, next_len)) { 195 /* 196 * Don't warn on bad regs->bp. An interrupt in entry code 197 * might cause a false positive warning. 198 */ 199 if (state->regs) 200 goto the_end; 201 202 goto bad_address; 203 } 204 205 /* Make sure it only unwinds up and doesn't overlap the last frame: */ 206 if (state->stack_info.type == prev_type) { 207 if (state->regs && (void *)next_frame < (void *)state->regs + regs_size(state->regs)) 208 goto bad_address; 209 210 if (state->bp && (void *)next_frame < (void *)state->bp + FRAME_HEADER_SIZE) 211 goto bad_address; 212 } 213 214 /* move to the next frame */ 215 if (regs) { 216 state->regs = regs; 217 state->bp = NULL; 218 } else { 219 state->bp = next_bp; 220 state->regs = NULL; 221 } 222 223 return true; 224 225 bad_address: 226 /* 227 * When unwinding a non-current task, the task might actually be 228 * running on another CPU, in which case it could be modifying its 229 * stack while we're reading it. This is generally not a problem and 230 * can be ignored as long as the caller understands that unwinding 231 * another task will not always succeed. 232 */ 233 if (state->task != current) 234 goto the_end; 235 236 if (state->regs) { 237 printk_deferred_once(KERN_WARNING 238 "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n", 239 state->regs, state->task->comm, 240 state->task->pid, next_frame); 241 unwind_dump(state, (unsigned long *)state->regs); 242 } else { 243 printk_deferred_once(KERN_WARNING 244 "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n", 245 state->bp, state->task->comm, 246 state->task->pid, next_frame); 247 unwind_dump(state, state->bp); 248 } 249 the_end: 250 state->stack_info.type = STACK_TYPE_UNKNOWN; 251 return false; 252 } 253 EXPORT_SYMBOL_GPL(unwind_next_frame); 254 255 void __unwind_start(struct unwind_state *state, struct task_struct *task, 256 struct pt_regs *regs, unsigned long *first_frame) 257 { 258 unsigned long *bp, *frame; 259 size_t len; 260 261 memset(state, 0, sizeof(*state)); 262 state->task = task; 263 264 /* don't even attempt to start from user mode regs */ 265 if (regs && user_mode(regs)) { 266 state->stack_info.type = STACK_TYPE_UNKNOWN; 267 return; 268 } 269 270 /* set up the starting stack frame */ 271 bp = get_frame_pointer(task, regs); 272 regs = decode_frame_pointer(bp); 273 if (regs) { 274 state->regs = regs; 275 frame = (unsigned long *)regs; 276 len = sizeof(*regs); 277 } else { 278 state->bp = bp; 279 frame = bp; 280 len = FRAME_HEADER_SIZE; 281 } 282 283 /* initialize stack info and make sure the frame data is accessible */ 284 get_stack_info(frame, state->task, &state->stack_info, 285 &state->stack_mask); 286 update_stack_state(state, frame, len); 287 288 /* 289 * The caller can provide the address of the first frame directly 290 * (first_frame) or indirectly (regs->sp) to indicate which stack frame 291 * to start unwinding at. Skip ahead until we reach it. 292 */ 293 while (!unwind_done(state) && 294 (!on_stack(&state->stack_info, first_frame, sizeof(long)) || 295 state->bp < first_frame)) 296 unwind_next_frame(state); 297 } 298 EXPORT_SYMBOL_GPL(__unwind_start); 299