summaryrefslogtreecommitdiff
path: root/arch/x86/kernel/unwind_frame.c
blob: d8ba93778ae325886f92f8bcba9d7db5f19fc97a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/interrupt.h>
#include <asm/sections.h>
#include <asm/ptrace.h>
#include <asm/bitops.h>
#include <asm/stacktrace.h>
#include <asm/unwind.h>

#define FRAME_HEADER_SIZE (sizeof(long) * 2)

unsigned long unwind_get_return_address(struct unwind_state *state)
{
	if (unwind_done(state))
		return 0;

	return __kernel_text_address(state->ip) ? state->ip : 0;
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);

unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
{
	if (unwind_done(state))
		return NULL;

	return state->regs ? &state->regs->ip : state->bp + 1;
}

static void unwind_dump(struct unwind_state *state)
{
	static bool dumped_before = false;
	bool prev_zero, zero = false;
	unsigned long word, *sp;
	struct stack_info stack_info = {0};
	unsigned long visit_mask = 0;

	if (dumped_before)
		return;

	dumped_before = true;

	printk_deferred("unwind stack type:%d next_sp:%p mask:0x%lx graph_idx:%d\n",
			state->stack_info.type, state->stack_info.next_sp,
			state->stack_mask, state->graph_idx);

	for (sp = PTR_ALIGN(state->orig_sp, sizeof(long)); sp;
	     sp = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
		if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
			break;

		for (; sp < stack_info.end; sp++) {

			word = READ_ONCE_NOCHECK(*sp);

			prev_zero = zero;
			zero = word == 0;

			if (zero) {
				if (!prev_zero)
					printk_deferred("%p: %0*x ...\n",
							sp, BITS_PER_LONG/4, 0);
				continue;
			}

			printk_deferred("%p: %0*lx (%pB)\n",
					sp, BITS_PER_LONG/4, word, (void *)word);
		}
	}
}

static bool in_entry_code(unsigned long ip)
{
	char *addr = (char *)ip;

	return addr >= __entry_text_start && addr < __entry_text_end;
}

static inline unsigned long *last_frame(struct unwind_state *state)
{
	return (unsigned long *)task_pt_regs(state->task) - 2;
}

static bool is_last_frame(struct unwind_state *state)
{
	return state->bp == last_frame(state);
}

#ifdef CONFIG_X86_32
#define GCC_REALIGN_WORDS 3
#else
#define GCC_REALIGN_WORDS 1
#endif

static inline unsigned long *last_aligned_frame(struct unwind_state *state)
{
	return last_frame(state) - GCC_REALIGN_WORDS;
}

static bool is_last_aligned_frame(struct unwind_state *state)
{
	unsigned long *last_bp = last_frame(state);
	unsigned long *aligned_bp = last_aligned_frame(state);

	/*
	 * GCC can occasionally decide to realign the stack pointer and change
	 * the offset of the stack frame in the prologue of a function called
	 * by head/entry code.  Examples:
	 *
	 * <start_secondary>:
	 *      push   %edi
	 *      lea    0x8(%esp),%edi
	 *      and    $0xfffffff8,%esp
	 *      pushl  -0x4(%edi)
	 *      push   %ebp
	 *      mov    %esp,%ebp
	 *
	 * <x86_64_start_kernel>:
	 *      lea    0x8(%rsp),%r10
	 *      and    $0xfffffffffffffff0,%rsp
	 *      pushq  -0x8(%r10)
	 *      push   %rbp
	 *      mov    %rsp,%rbp
	 *
	 * After aligning the stack, it pushes a duplicate copy of the return
	 * address before pushing the frame pointer.
	 */
	return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
}

static bool is_last_ftrace_frame(struct unwind_state *state)
{
	unsigned long *last_bp = last_frame(state);
	unsigned long *last_ftrace_bp = last_bp - 3;

	/*
	 * When unwinding from an ftrace handler of a function called by entry
	 * code, the stack layout of the last frame is:
	 *
	 *   bp
	 *   parent ret addr
	 *   bp
	 *   function ret addr
	 *   parent ret addr
	 *   pt_regs
	 *   -----------------
	 */
	return (state->bp == last_ftrace_bp &&
		*state->bp == *(state->bp + 2) &&
		*(state->bp + 1) == *(state->bp + 4));
}

static bool is_last_task_frame(struct unwind_state *state)
{
	return is_last_frame(state) || is_last_aligned_frame(state) ||
	       is_last_ftrace_frame(state);
}

/*
 * This determines if the frame pointer actually contains an encoded pointer to
 * pt_regs on the stack.  See ENCODE_FRAME_POINTER.
 */
#ifdef CONFIG_X86_64
static struct pt_regs *decode_frame_pointer(unsigned long *bp)
{
	unsigned long regs = (unsigned long)bp;

	if (!(regs & 0x1))
		return NULL;

	return (struct pt_regs *)(regs & ~0x1);
}
#else
static struct pt_regs *decode_frame_pointer(unsigned long *bp)
{
	unsigned long regs = (unsigned long)bp;

	if (regs & 0x80000000)
		return NULL;

	return (struct pt_regs *)(regs | 0x80000000);
}
#endif

/*
 * While walking the stack, KMSAN may stomp on stale locals from other
 * functions that were marked as uninitialized upon function exit, and
 * now hold the call frame information for the current function (e.g. the frame
 * pointer). Because KMSAN does not specifically mark call frames as
 * initialized, false positive reports are possible. To prevent such reports,
 * we mark the functions scanning the stack (here and below) with
 * __no_kmsan_checks.
 */
__no_kmsan_checks
static bool update_stack_state(struct unwind_state *state,
			       unsigned long *next_bp)
{
	struct stack_info *info = &state->stack_info;
	enum stack_type prev_type = info->type;
	struct pt_regs *regs;
	unsigned long *frame, *prev_frame_end, *addr_p, addr;
	size_t len;

	if (state->regs)
		prev_frame_end = (void *)state->regs + sizeof(*state->regs);
	else
		prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE;

	/* Is the next frame pointer an encoded pointer to pt_regs? */
	regs = decode_frame_pointer(next_bp);
	if (regs) {
		frame = (unsigned long *)regs;
		len = sizeof(*regs);
		state->got_irq = true;
	} else {
		frame = next_bp;
		len = FRAME_HEADER_SIZE;
	}

	/*
	 * If the next bp isn't on the current stack, switch to the next one.
	 *
	 * We may have to traverse multiple stacks to deal with the possibility
	 * that info->next_sp could point to an empty stack and the next bp
	 * could be on a subsequent stack.
	 */
	while (!on_stack(info, frame, len))
		if (get_stack_info(info->next_sp, state->task, info,
				   &state->stack_mask))
			return false;

	/* Make sure it only unwinds up and doesn't overlap the prev frame: */
	if (state->orig_sp && state->stack_info.type == prev_type &&
	    frame < prev_frame_end)
		return false;

	/* Move state to the next frame: */
	if (regs) {
		state->regs = regs;
		state->bp = NULL;
	} else {
		state->bp = next_bp;
		state->regs = NULL;
	}

	/* Save the return address: */
	if (state->regs && user_mode(state->regs))
		state->ip = 0;
	else {
		addr_p = unwind_get_return_address_ptr(state);
		addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
		state->ip = unwind_recover_ret_addr(state, addr, addr_p);
	}

	/* Save the original stack pointer for unwind_dump(): */
	if (!state->orig_sp)
		state->orig_sp = frame;

	return true;
}

__no_kmsan_checks
bool unwind_next_frame(struct unwind_state *state)
{
	struct pt_regs *regs;
	unsigned long *next_bp;

	if (unwind_done(state))
		return false;

	/* Have we reached the end? */
	if (state->regs && user_mode(state->regs))
		goto the_end;

	if (is_last_task_frame(state)) {
		regs = task_pt_regs(state->task);

		/*
		 * kthreads (other than the boot CPU's idle thread) have some
		 * partial regs at the end of their stack which were placed
		 * there by copy_thread().  But the regs don't have any
		 * useful information, so we can skip them.
		 *
		 * This user_mode() check is slightly broader than a PF_KTHREAD
		 * check because it also catches the awkward situation where a
		 * newly forked kthread transitions into a user task by calling
		 * kernel_execve(), which eventually clears PF_KTHREAD.
		 */
		if (!user_mode(regs))
			goto the_end;

		/*
		 * We're almost at the end, but not quite: there's still the
		 * syscall regs frame.  Entry code doesn't encode the regs
		 * pointer for syscalls, so we have to set it manually.
		 */
		state->regs = regs;
		state->bp = NULL;
		state->ip = 0;
		return true;
	}

	/* Get the next frame pointer: */
	if (state->next_bp) {
		next_bp = state->next_bp;
		state->next_bp = NULL;
	} else if (state->regs) {
		next_bp = (unsigned long *)state->regs->bp;
	} else {
		next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);
	}

	/* Move to the next frame if it's safe: */
	if (!update_stack_state(state, next_bp))
		goto bad_address;

	return true;

bad_address:
	state->error = true;

	/*
	 * When unwinding a non-current task, the task might actually be
	 * running on another CPU, in which case it could be modifying its
	 * stack while we're reading it.  This is generally not a problem and
	 * can be ignored as long as the caller understands that unwinding
	 * another task will not always succeed.
	 */
	if (state->task != current)
		goto the_end;

	/*
	 * Don't warn if the unwinder got lost due to an interrupt in entry
	 * code or in the C handler before the first frame pointer got set up:
	 */
	if (state->got_irq && in_entry_code(state->ip))
		goto the_end;
	if (state->regs &&
	    state->regs->sp >= (unsigned long)last_aligned_frame(state) &&
	    state->regs->sp < (unsigned long)task_pt_regs(state->task))
		goto the_end;

	/*
	 * There are some known frame pointer issues on 32-bit.  Disable
	 * unwinder warnings on 32-bit until it gets objtool support.
	 */
	if (IS_ENABLED(CONFIG_X86_32))
		goto the_end;

	if (state->task != current)
		goto the_end;

	if (state->regs) {
		printk_deferred_once(KERN_WARNING
			"WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
			state->regs, state->task->comm,
			state->task->pid, next_bp);
		unwind_dump(state);
	} else {
		printk_deferred_once(KERN_WARNING
			"WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
			state->bp, state->task->comm,
			state->task->pid, next_bp);
		unwind_dump(state);
	}
the_end:
	state->stack_info.type = STACK_TYPE_UNKNOWN;
	return false;
}
EXPORT_SYMBOL_GPL(unwind_next_frame);

void __unwind_start(struct unwind_state *state, struct task_struct *task,
		    struct pt_regs *regs, unsigned long *first_frame)
{
	unsigned long *bp;

	memset(state, 0, sizeof(*state));
	state->task = task;
	state->got_irq = (regs);

	/* Don't even attempt to start from user mode regs: */
	if (regs && user_mode(regs)) {
		state->stack_info.type = STACK_TYPE_UNKNOWN;
		return;
	}

	bp = get_frame_pointer(task, regs);

	/*
	 * If we crash with IP==0, the last successfully executed instruction
	 * was probably an indirect function call with a NULL function pointer.
	 * That means that SP points into the middle of an incomplete frame:
	 * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we
	 * would have written a frame pointer if we hadn't crashed.
	 * Pretend that the frame is complete and that BP points to it, but save
	 * the real BP so that we can use it when looking for the next frame.
	 */
	if (regs && regs->ip == 0 && (unsigned long *)regs->sp >= first_frame) {
		state->next_bp = bp;
		bp = ((unsigned long *)regs->sp) - 1;
	}

	/* Initialize stack info and make sure the frame data is accessible: */
	get_stack_info(bp, state->task, &state->stack_info,
		       &state->stack_mask);
	update_stack_state(state, bp);

	/*
	 * The caller can provide the address of the first frame directly
	 * (first_frame) or indirectly (regs->sp) to indicate which stack frame
	 * to start unwinding at.  Skip ahead until we reach it.
	 */
	while (!unwind_done(state) &&
	       (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
			(state->next_bp == NULL && state->bp < first_frame)))
		unwind_next_frame(state);
}
EXPORT_SYMBOL_GPL(__unwind_start);