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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 if (addr >= __entry_text_start && addr < __entry_text_end)
78 return true;
79
80 if (addr >= __irqentry_text_start && addr < __irqentry_text_end)
81 return true;
82
83 return false;
84}
85
86static inline unsigned long *last_frame(struct unwind_state *state)
87{
88 return (unsigned long *)task_pt_regs(state->task) - 2;
89}
90
91static bool is_last_frame(struct unwind_state *state)
92{
93 return state->bp == last_frame(state);
94}
95
96#ifdef CONFIG_X86_32
97#define GCC_REALIGN_WORDS 3
98#else
99#define GCC_REALIGN_WORDS 1
100#endif
101
102static inline unsigned long *last_aligned_frame(struct unwind_state *state)
103{
104 return last_frame(state) - GCC_REALIGN_WORDS;
105}
106
107static bool is_last_aligned_frame(struct unwind_state *state)
108{
109 unsigned long *last_bp = last_frame(state);
110 unsigned long *aligned_bp = last_aligned_frame(state);
111
112 /*
113 * GCC can occasionally decide to realign the stack pointer and change
114 * the offset of the stack frame in the prologue of a function called
115 * by head/entry code. Examples:
116 *
117 * <start_secondary>:
118 * push %edi
119 * lea 0x8(%esp),%edi
120 * and $0xfffffff8,%esp
121 * pushl -0x4(%edi)
122 * push %ebp
123 * mov %esp,%ebp
124 *
125 * <x86_64_start_kernel>:
126 * lea 0x8(%rsp),%r10
127 * and $0xfffffffffffffff0,%rsp
128 * pushq -0x8(%r10)
129 * push %rbp
130 * mov %rsp,%rbp
131 *
132 * After aligning the stack, it pushes a duplicate copy of the return
133 * address before pushing the frame pointer.
134 */
135 return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
136}
137
138static bool is_last_ftrace_frame(struct unwind_state *state)
139{
140 unsigned long *last_bp = last_frame(state);
141 unsigned long *last_ftrace_bp = last_bp - 3;
142
143 /*
144 * When unwinding from an ftrace handler of a function called by entry
145 * code, the stack layout of the last frame is:
146 *
147 * bp
148 * parent ret addr
149 * bp
150 * function ret addr
151 * parent ret addr
152 * pt_regs
153 * -----------------
154 */
155 return (state->bp == last_ftrace_bp &&
156 *state->bp == *(state->bp + 2) &&
157 *(state->bp + 1) == *(state->bp + 4));
158}
159
160static bool is_last_task_frame(struct unwind_state *state)
161{
162 return is_last_frame(state) || is_last_aligned_frame(state) ||
163 is_last_ftrace_frame(state);
164}
165
166/*
167 * This determines if the frame pointer actually contains an encoded pointer to
168 * pt_regs on the stack. See ENCODE_FRAME_POINTER.
169 */
170#ifdef CONFIG_X86_64
171static struct pt_regs *decode_frame_pointer(unsigned long *bp)
172{
173 unsigned long regs = (unsigned long)bp;
174
175 if (!(regs & 0x1))
176 return NULL;
177
178 return (struct pt_regs *)(regs & ~0x1);
179}
180#else
181static struct pt_regs *decode_frame_pointer(unsigned long *bp)
182{
183 unsigned long regs = (unsigned long)bp;
184
185 if (regs & 0x80000000)
186 return NULL;
187
188 return (struct pt_regs *)(regs | 0x80000000);
189}
190#endif
191
192static bool update_stack_state(struct unwind_state *state,
193 unsigned long *next_bp)
194{
195 struct stack_info *info = &state->stack_info;
196 enum stack_type prev_type = info->type;
197 struct pt_regs *regs;
198 unsigned long *frame, *prev_frame_end, *addr_p, addr;
199 size_t len;
200
201 if (state->regs)
202 prev_frame_end = (void *)state->regs + sizeof(*state->regs);
203 else
204 prev_frame_end = (void *)state->bp + FRAME_HEADER_SIZE;
205
206 /* Is the next frame pointer an encoded pointer to pt_regs? */
207 regs = decode_frame_pointer(next_bp);
208 if (regs) {
209 frame = (unsigned long *)regs;
210 len = sizeof(*regs);
211 state->got_irq = true;
212 } else {
213 frame = next_bp;
214 len = FRAME_HEADER_SIZE;
215 }
216
217 /*
218 * If the next bp isn't on the current stack, switch to the next one.
219 *
220 * We may have to traverse multiple stacks to deal with the possibility
221 * that info->next_sp could point to an empty stack and the next bp
222 * could be on a subsequent stack.
223 */
224 while (!on_stack(info, frame, len))
225 if (get_stack_info(info->next_sp, state->task, info,
226 &state->stack_mask))
227 return false;
228
229 /* Make sure it only unwinds up and doesn't overlap the prev frame: */
230 if (state->orig_sp && state->stack_info.type == prev_type &&
231 frame < prev_frame_end)
232 return false;
233
234 /* Move state to the next frame: */
235 if (regs) {
236 state->regs = regs;
237 state->bp = NULL;
238 } else {
239 state->bp = next_bp;
240 state->regs = NULL;
241 }
242
243 /* Save the return address: */
244 if (state->regs && user_mode(state->regs))
245 state->ip = 0;
246 else {
247 addr_p = unwind_get_return_address_ptr(state);
248 addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
249 state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
250 addr, addr_p);
251 }
252
253 /* Save the original stack pointer for unwind_dump(): */
254 if (!state->orig_sp)
255 state->orig_sp = frame;
256
257 return true;
258}
259
260bool unwind_next_frame(struct unwind_state *state)
261{
262 struct pt_regs *regs;
263 unsigned long *next_bp;
264
265 if (unwind_done(state))
266 return false;
267
268 /* Have we reached the end? */
269 if (state->regs && user_mode(state->regs))
270 goto the_end;
271
272 if (is_last_task_frame(state)) {
273 regs = task_pt_regs(state->task);
274
275 /*
276 * kthreads (other than the boot CPU's idle thread) have some
277 * partial regs at the end of their stack which were placed
278 * there by copy_thread_tls(). But the regs don't have any
279 * useful information, so we can skip them.
280 *
281 * This user_mode() check is slightly broader than a PF_KTHREAD
282 * check because it also catches the awkward situation where a
283 * newly forked kthread transitions into a user task by calling
284 * do_execve(), which eventually clears PF_KTHREAD.
285 */
286 if (!user_mode(regs))
287 goto the_end;
288
289 /*
290 * We're almost at the end, but not quite: there's still the
291 * syscall regs frame. Entry code doesn't encode the regs
292 * pointer for syscalls, so we have to set it manually.
293 */
294 state->regs = regs;
295 state->bp = NULL;
296 state->ip = 0;
297 return true;
298 }
299
300 /* Get the next frame pointer: */
301 if (state->next_bp) {
302 next_bp = state->next_bp;
303 state->next_bp = NULL;
304 } else if (state->regs) {
305 next_bp = (unsigned long *)state->regs->bp;
306 } else {
307 next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);
308 }
309
310 /* Move to the next frame if it's safe: */
311 if (!update_stack_state(state, next_bp))
312 goto bad_address;
313
314 return true;
315
316bad_address:
317 state->error = true;
318
319 /*
320 * When unwinding a non-current task, the task might actually be
321 * running on another CPU, in which case it could be modifying its
322 * stack while we're reading it. This is generally not a problem and
323 * can be ignored as long as the caller understands that unwinding
324 * another task will not always succeed.
325 */
326 if (state->task != current)
327 goto the_end;
328
329 /*
330 * Don't warn if the unwinder got lost due to an interrupt in entry
331 * code or in the C handler before the first frame pointer got set up:
332 */
333 if (state->got_irq && in_entry_code(state->ip))
334 goto the_end;
335 if (state->regs &&
336 state->regs->sp >= (unsigned long)last_aligned_frame(state) &&
337 state->regs->sp < (unsigned long)task_pt_regs(state->task))
338 goto the_end;
339
340 /*
341 * There are some known frame pointer issues on 32-bit. Disable
342 * unwinder warnings on 32-bit until it gets objtool support.
343 */
344 if (IS_ENABLED(CONFIG_X86_32))
345 goto the_end;
346
347 if (state->regs) {
348 printk_deferred_once(KERN_WARNING
349 "WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
350 state->regs, state->task->comm,
351 state->task->pid, next_bp);
352 unwind_dump(state);
353 } else {
354 printk_deferred_once(KERN_WARNING
355 "WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
356 state->bp, state->task->comm,
357 state->task->pid, next_bp);
358 unwind_dump(state);
359 }
360the_end:
361 state->stack_info.type = STACK_TYPE_UNKNOWN;
362 return false;
363}
364EXPORT_SYMBOL_GPL(unwind_next_frame);
365
366void __unwind_start(struct unwind_state *state, struct task_struct *task,
367 struct pt_regs *regs, unsigned long *first_frame)
368{
369 unsigned long *bp;
370
371 memset(state, 0, sizeof(*state));
372 state->task = task;
373 state->got_irq = (regs);
374
375 /* Don't even attempt to start from user mode regs: */
376 if (regs && user_mode(regs)) {
377 state->stack_info.type = STACK_TYPE_UNKNOWN;
378 return;
379 }
380
381 bp = get_frame_pointer(task, regs);
382
383 /*
384 * If we crash with IP==0, the last successfully executed instruction
385 * was probably an indirect function call with a NULL function pointer.
386 * That means that SP points into the middle of an incomplete frame:
387 * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we
388 * would have written a frame pointer if we hadn't crashed.
389 * Pretend that the frame is complete and that BP points to it, but save
390 * the real BP so that we can use it when looking for the next frame.
391 */
392 if (regs && regs->ip == 0 && (unsigned long *)regs->sp >= first_frame) {
393 state->next_bp = bp;
394 bp = ((unsigned long *)regs->sp) - 1;
395 }
396
397 /* Initialize stack info and make sure the frame data is accessible: */
398 get_stack_info(bp, state->task, &state->stack_info,
399 &state->stack_mask);
400 update_stack_state(state, bp);
401
402 /*
403 * The caller can provide the address of the first frame directly
404 * (first_frame) or indirectly (regs->sp) to indicate which stack frame
405 * to start unwinding at. Skip ahead until we reach it.
406 */
407 while (!unwind_done(state) &&
408 (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
409 (state->next_bp == NULL && state->bp < first_frame)))
410 unwind_next_frame(state);
411}
412EXPORT_SYMBOL_GPL(__unwind_start);