summaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/unwind_frame.c
blob: 478d15dbaee41b251c8bb28b59183e2b6c733326 (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
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <asm/ptrace.h>
#include <asm/bitops.h>
#include <asm/stacktrace.h>
#include <asm/unwind.h>

#define FRAME_HEADER_SIZE (sizeof(long) * 2)

/*
 * This disables KASAN checking when reading a value from another task's stack,
 * since the other task could be running on another CPU and could have poisoned
 * the stack in the meantime.
 */
#define READ_ONCE_TASK_STACK(task, x)			\
({							\
	unsigned long val;				\
	if (task == current)				\
		val = READ_ONCE(x);			\
	else						\
		val = READ_ONCE_NOCHECK(x);		\
	val;						\
})

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

	if (dumped_before)
		return;

	dumped_before = true;

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

	for (sp = state->orig_sp; sp < state->stack_info.end; sp++) {
		word = READ_ONCE_NOCHECK(*sp);

		prev_zero = zero;
		zero = word == 0;

		if (zero) {
			if (!prev_zero)
				printk_deferred("%p: %016x ...\n", sp, 0);
			continue;
		}

		printk_deferred("%p: %016lx (%pB)\n", sp, word, (void *)word);
	}
}

unsigned long unwind_get_return_address(struct unwind_state *state)
{
	unsigned long addr;
	unsigned long *addr_p = unwind_get_return_address_ptr(state);

	if (unwind_done(state))
		return 0;

	if (state->regs && user_mode(state->regs))
		return 0;

	addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
	addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, addr,
				     addr_p);

	return __kernel_text_address(addr) ? addr : 0;
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);

static size_t regs_size(struct pt_regs *regs)
{
	/* x86_32 regs from kernel mode are two words shorter: */
	if (IS_ENABLED(CONFIG_X86_32) && !user_mode(regs))
		return sizeof(*regs) - 2*sizeof(long);

	return sizeof(*regs);
}

static bool is_last_task_frame(struct unwind_state *state)
{
	unsigned long bp = (unsigned long)state->bp;
	unsigned long regs = (unsigned long)task_pt_regs(state->task);

	/*
	 * We have to check for the last task frame at two different locations
	 * because gcc can occasionally decide to realign the stack pointer and
	 * change the offset of the stack frame by a word in the prologue of a
	 * function called by head/entry code.
	 */
	return bp == regs - FRAME_HEADER_SIZE ||
	       bp == regs - FRAME_HEADER_SIZE - sizeof(long);
}

/*
 * This determines if the frame pointer actually contains an encoded pointer to
 * pt_regs on the stack.  See ENCODE_FRAME_POINTER.
 */
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);
}

static bool update_stack_state(struct unwind_state *state, void *addr,
			       size_t len)
{
	struct stack_info *info = &state->stack_info;
	enum stack_type orig_type = info->type;

	/*
	 * If addr 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 'addr' could
	 * be on a subsequent stack.
	 */
	while (!on_stack(info, addr, len))
		if (get_stack_info(info->next_sp, state->task, info,
				   &state->stack_mask))
			return false;

	if (!state->orig_sp || info->type != orig_type)
		state->orig_sp = addr;

	return true;
}

bool unwind_next_frame(struct unwind_state *state)
{
	struct pt_regs *regs;
	unsigned long *next_bp, *next_frame;
	size_t next_len;
	enum stack_type prev_type = state->stack_info.type;

	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_tls().  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
		 * do_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;
		return true;
	}

	/* get the next frame pointer */
	if (state->regs)
		next_bp = (unsigned long *)state->regs->bp;
	else
		next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task,*state->bp);

	/* is the next frame pointer an encoded pointer to pt_regs? */
	regs = decode_frame_pointer(next_bp);
	if (regs) {
		next_frame = (unsigned long *)regs;
		next_len = sizeof(*regs);
	} else {
		next_frame = next_bp;
		next_len = FRAME_HEADER_SIZE;
	}

	/* make sure the next frame's data is accessible */
	if (!update_stack_state(state, next_frame, next_len)) {
		/*
		 * Don't warn on bad regs->bp.  An interrupt in entry code
		 * might cause a false positive warning.
		 */
		if (state->regs)
			goto the_end;

		goto bad_address;
	}

	/* Make sure it only unwinds up and doesn't overlap the last frame: */
	if (state->stack_info.type == prev_type) {
		if (state->regs && (void *)next_frame < (void *)state->regs + regs_size(state->regs))
			goto bad_address;

		if (state->bp && (void *)next_frame < (void *)state->bp + FRAME_HEADER_SIZE)
			goto bad_address;
	}

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

	return true;

bad_address:
	/*
	 * 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;

	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_frame);
		unwind_dump(state, (unsigned long *)state->regs);
	} 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_frame);
		unwind_dump(state, state->bp);
	}
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, *frame;
	size_t len;

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

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

	/* set up the starting stack frame */
	bp = get_frame_pointer(task, regs);
	regs = decode_frame_pointer(bp);
	if (regs) {
		state->regs = regs;
		frame = (unsigned long *)regs;
		len = sizeof(*regs);
	} else {
		state->bp = bp;
		frame = bp;
		len = FRAME_HEADER_SIZE;
	}

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

	/*
	 * 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->bp < first_frame))
		unwind_next_frame(state);
}
EXPORT_SYMBOL_GPL(__unwind_start);