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
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