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
14unsigned 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}
21EXPORT_SYMBOL_GPL(unwind_get_return_address);
22
23unsigned 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
31static 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
73static 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
80static inline unsigned long *last_frame(struct unwind_state *state)
81{
82	return (unsigned long *)task_pt_regs(state->task) - 2;
83}
84
85static 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
96static inline unsigned long *last_aligned_frame(struct unwind_state *state)
97{
98	return last_frame(state) - GCC_REALIGN_WORDS;
99}
100
101static 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
132static 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
154static 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
165static 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
175static 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
196static 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
264bool 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
320bad_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	}
367the_end:
368	state->stack_info.type = STACK_TYPE_UNKNOWN;
369	return false;
370}
371EXPORT_SYMBOL_GPL(unwind_next_frame);
372
373void __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}
419EXPORT_SYMBOL_GPL(__unwind_start);
420