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d83a7cb3 JP |
1 | /* |
2 | * transition.c - Kernel Live Patching transition functions | |
3 | * | |
4 | * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com> | |
5 | * | |
6 | * This program is free software; you can redistribute it and/or | |
7 | * modify it under the terms of the GNU General Public License | |
8 | * as published by the Free Software Foundation; either version 2 | |
9 | * of the License, or (at your option) any later version. | |
10 | * | |
11 | * This program is distributed in the hope that it will be useful, | |
12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | * GNU General Public License for more details. | |
15 | * | |
16 | * You should have received a copy of the GNU General Public License | |
17 | * along with this program; if not, see <http://www.gnu.org/licenses/>. | |
18 | */ | |
19 | ||
20 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt | |
21 | ||
22 | #include <linux/cpu.h> | |
23 | #include <linux/stacktrace.h> | |
10517429 | 24 | #include "core.h" |
d83a7cb3 JP |
25 | #include "patch.h" |
26 | #include "transition.h" | |
27 | #include "../sched/sched.h" | |
28 | ||
29 | #define MAX_STACK_ENTRIES 100 | |
30 | #define STACK_ERR_BUF_SIZE 128 | |
31 | ||
d83a7cb3 JP |
32 | struct klp_patch *klp_transition_patch; |
33 | ||
34 | static int klp_target_state = KLP_UNDEFINED; | |
35 | ||
36 | /* | |
37 | * This work can be performed periodically to finish patching or unpatching any | |
38 | * "straggler" tasks which failed to transition in the first attempt. | |
39 | */ | |
40 | static void klp_transition_work_fn(struct work_struct *work) | |
41 | { | |
42 | mutex_lock(&klp_mutex); | |
43 | ||
44 | if (klp_transition_patch) | |
45 | klp_try_complete_transition(); | |
46 | ||
47 | mutex_unlock(&klp_mutex); | |
48 | } | |
49 | static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn); | |
50 | ||
842c0884 PM |
51 | /* |
52 | * This function is just a stub to implement a hard force | |
53 | * of synchronize_sched(). This requires synchronizing | |
54 | * tasks even in userspace and idle. | |
55 | */ | |
56 | static void klp_sync(struct work_struct *work) | |
57 | { | |
58 | } | |
59 | ||
60 | /* | |
61 | * We allow to patch also functions where RCU is not watching, | |
62 | * e.g. before user_exit(). We can not rely on the RCU infrastructure | |
63 | * to do the synchronization. Instead hard force the sched synchronization. | |
64 | * | |
65 | * This approach allows to use RCU functions for manipulating func_stack | |
66 | * safely. | |
67 | */ | |
68 | static void klp_synchronize_transition(void) | |
69 | { | |
70 | schedule_on_each_cpu(klp_sync); | |
71 | } | |
72 | ||
d83a7cb3 JP |
73 | /* |
74 | * The transition to the target patch state is complete. Clean up the data | |
75 | * structures. | |
76 | */ | |
77 | static void klp_complete_transition(void) | |
78 | { | |
79 | struct klp_object *obj; | |
80 | struct klp_func *func; | |
81 | struct task_struct *g, *task; | |
82 | unsigned int cpu; | |
3ec24776 | 83 | bool immediate_func = false; |
d83a7cb3 JP |
84 | |
85 | if (klp_target_state == KLP_UNPATCHED) { | |
86 | /* | |
87 | * All tasks have transitioned to KLP_UNPATCHED so we can now | |
88 | * remove the new functions from the func_stack. | |
89 | */ | |
90 | klp_unpatch_objects(klp_transition_patch); | |
91 | ||
92 | /* | |
93 | * Make sure klp_ftrace_handler() can no longer see functions | |
94 | * from this patch on the ops->func_stack. Otherwise, after | |
95 | * func->transition gets cleared, the handler may choose a | |
96 | * removed function. | |
97 | */ | |
842c0884 | 98 | klp_synchronize_transition(); |
d83a7cb3 JP |
99 | } |
100 | ||
101 | if (klp_transition_patch->immediate) | |
102 | goto done; | |
103 | ||
3ec24776 JP |
104 | klp_for_each_object(klp_transition_patch, obj) { |
105 | klp_for_each_func(obj, func) { | |
d83a7cb3 | 106 | func->transition = false; |
3ec24776 JP |
107 | if (func->immediate) |
108 | immediate_func = true; | |
109 | } | |
110 | } | |
111 | ||
112 | if (klp_target_state == KLP_UNPATCHED && !immediate_func) | |
113 | module_put(klp_transition_patch->mod); | |
d83a7cb3 JP |
114 | |
115 | /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ | |
116 | if (klp_target_state == KLP_PATCHED) | |
842c0884 | 117 | klp_synchronize_transition(); |
d83a7cb3 JP |
118 | |
119 | read_lock(&tasklist_lock); | |
120 | for_each_process_thread(g, task) { | |
121 | WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); | |
122 | task->patch_state = KLP_UNDEFINED; | |
123 | } | |
124 | read_unlock(&tasklist_lock); | |
125 | ||
126 | for_each_possible_cpu(cpu) { | |
127 | task = idle_task(cpu); | |
128 | WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); | |
129 | task->patch_state = KLP_UNDEFINED; | |
130 | } | |
131 | ||
132 | done: | |
133 | klp_target_state = KLP_UNDEFINED; | |
134 | klp_transition_patch = NULL; | |
135 | } | |
136 | ||
137 | /* | |
138 | * This is called in the error path, to cancel a transition before it has | |
139 | * started, i.e. klp_init_transition() has been called but | |
140 | * klp_start_transition() hasn't. If the transition *has* been started, | |
141 | * klp_reverse_transition() should be used instead. | |
142 | */ | |
143 | void klp_cancel_transition(void) | |
144 | { | |
3ec24776 JP |
145 | if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED)) |
146 | return; | |
147 | ||
148 | klp_target_state = KLP_UNPATCHED; | |
d83a7cb3 JP |
149 | klp_complete_transition(); |
150 | } | |
151 | ||
152 | /* | |
153 | * Switch the patched state of the task to the set of functions in the target | |
154 | * patch state. | |
155 | * | |
156 | * NOTE: If task is not 'current', the caller must ensure the task is inactive. | |
157 | * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value. | |
158 | */ | |
159 | void klp_update_patch_state(struct task_struct *task) | |
160 | { | |
842c0884 PM |
161 | /* |
162 | * A variant of synchronize_sched() is used to allow patching functions | |
163 | * where RCU is not watching, see klp_synchronize_transition(). | |
164 | */ | |
165 | preempt_disable_notrace(); | |
d83a7cb3 JP |
166 | |
167 | /* | |
168 | * This test_and_clear_tsk_thread_flag() call also serves as a read | |
169 | * barrier (smp_rmb) for two cases: | |
170 | * | |
171 | * 1) Enforce the order of the TIF_PATCH_PENDING read and the | |
172 | * klp_target_state read. The corresponding write barrier is in | |
173 | * klp_init_transition(). | |
174 | * | |
175 | * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read | |
176 | * of func->transition, if klp_ftrace_handler() is called later on | |
177 | * the same CPU. See __klp_disable_patch(). | |
178 | */ | |
179 | if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING)) | |
180 | task->patch_state = READ_ONCE(klp_target_state); | |
181 | ||
842c0884 | 182 | preempt_enable_notrace(); |
d83a7cb3 JP |
183 | } |
184 | ||
185 | /* | |
186 | * Determine whether the given stack trace includes any references to a | |
187 | * to-be-patched or to-be-unpatched function. | |
188 | */ | |
189 | static int klp_check_stack_func(struct klp_func *func, | |
190 | struct stack_trace *trace) | |
191 | { | |
192 | unsigned long func_addr, func_size, address; | |
193 | struct klp_ops *ops; | |
194 | int i; | |
195 | ||
196 | if (func->immediate) | |
197 | return 0; | |
198 | ||
199 | for (i = 0; i < trace->nr_entries; i++) { | |
200 | address = trace->entries[i]; | |
201 | ||
202 | if (klp_target_state == KLP_UNPATCHED) { | |
203 | /* | |
204 | * Check for the to-be-unpatched function | |
205 | * (the func itself). | |
206 | */ | |
207 | func_addr = (unsigned long)func->new_func; | |
208 | func_size = func->new_size; | |
209 | } else { | |
210 | /* | |
211 | * Check for the to-be-patched function | |
212 | * (the previous func). | |
213 | */ | |
214 | ops = klp_find_ops(func->old_addr); | |
215 | ||
216 | if (list_is_singular(&ops->func_stack)) { | |
217 | /* original function */ | |
218 | func_addr = func->old_addr; | |
219 | func_size = func->old_size; | |
220 | } else { | |
221 | /* previously patched function */ | |
222 | struct klp_func *prev; | |
223 | ||
224 | prev = list_next_entry(func, stack_node); | |
225 | func_addr = (unsigned long)prev->new_func; | |
226 | func_size = prev->new_size; | |
227 | } | |
228 | } | |
229 | ||
230 | if (address >= func_addr && address < func_addr + func_size) | |
231 | return -EAGAIN; | |
232 | } | |
233 | ||
234 | return 0; | |
235 | } | |
236 | ||
237 | /* | |
238 | * Determine whether it's safe to transition the task to the target patch state | |
239 | * by looking for any to-be-patched or to-be-unpatched functions on its stack. | |
240 | */ | |
241 | static int klp_check_stack(struct task_struct *task, char *err_buf) | |
242 | { | |
243 | static unsigned long entries[MAX_STACK_ENTRIES]; | |
244 | struct stack_trace trace; | |
245 | struct klp_object *obj; | |
246 | struct klp_func *func; | |
247 | int ret; | |
248 | ||
249 | trace.skip = 0; | |
250 | trace.nr_entries = 0; | |
251 | trace.max_entries = MAX_STACK_ENTRIES; | |
252 | trace.entries = entries; | |
253 | ret = save_stack_trace_tsk_reliable(task, &trace); | |
254 | WARN_ON_ONCE(ret == -ENOSYS); | |
255 | if (ret) { | |
256 | snprintf(err_buf, STACK_ERR_BUF_SIZE, | |
257 | "%s: %s:%d has an unreliable stack\n", | |
258 | __func__, task->comm, task->pid); | |
259 | return ret; | |
260 | } | |
261 | ||
262 | klp_for_each_object(klp_transition_patch, obj) { | |
263 | if (!obj->patched) | |
264 | continue; | |
265 | klp_for_each_func(obj, func) { | |
266 | ret = klp_check_stack_func(func, &trace); | |
267 | if (ret) { | |
268 | snprintf(err_buf, STACK_ERR_BUF_SIZE, | |
269 | "%s: %s:%d is sleeping on function %s\n", | |
270 | __func__, task->comm, task->pid, | |
271 | func->old_name); | |
272 | return ret; | |
273 | } | |
274 | } | |
275 | } | |
276 | ||
277 | return 0; | |
278 | } | |
279 | ||
280 | /* | |
281 | * Try to safely switch a task to the target patch state. If it's currently | |
282 | * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or | |
283 | * if the stack is unreliable, return false. | |
284 | */ | |
285 | static bool klp_try_switch_task(struct task_struct *task) | |
286 | { | |
287 | struct rq *rq; | |
288 | struct rq_flags flags; | |
289 | int ret; | |
290 | bool success = false; | |
291 | char err_buf[STACK_ERR_BUF_SIZE]; | |
292 | ||
293 | err_buf[0] = '\0'; | |
294 | ||
295 | /* check if this task has already switched over */ | |
296 | if (task->patch_state == klp_target_state) | |
297 | return true; | |
298 | ||
299 | /* | |
300 | * For arches which don't have reliable stack traces, we have to rely | |
301 | * on other methods (e.g., switching tasks at kernel exit). | |
302 | */ | |
303 | if (!klp_have_reliable_stack()) | |
304 | return false; | |
305 | ||
306 | /* | |
307 | * Now try to check the stack for any to-be-patched or to-be-unpatched | |
308 | * functions. If all goes well, switch the task to the target patch | |
309 | * state. | |
310 | */ | |
311 | rq = task_rq_lock(task, &flags); | |
312 | ||
313 | if (task_running(rq, task) && task != current) { | |
314 | snprintf(err_buf, STACK_ERR_BUF_SIZE, | |
315 | "%s: %s:%d is running\n", __func__, task->comm, | |
316 | task->pid); | |
317 | goto done; | |
318 | } | |
319 | ||
320 | ret = klp_check_stack(task, err_buf); | |
321 | if (ret) | |
322 | goto done; | |
323 | ||
324 | success = true; | |
325 | ||
326 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
327 | task->patch_state = klp_target_state; | |
328 | ||
329 | done: | |
330 | task_rq_unlock(rq, task, &flags); | |
331 | ||
332 | /* | |
333 | * Due to console deadlock issues, pr_debug() can't be used while | |
334 | * holding the task rq lock. Instead we have to use a temporary buffer | |
335 | * and print the debug message after releasing the lock. | |
336 | */ | |
337 | if (err_buf[0] != '\0') | |
338 | pr_debug("%s", err_buf); | |
339 | ||
340 | return success; | |
341 | ||
342 | } | |
343 | ||
344 | /* | |
345 | * Try to switch all remaining tasks to the target patch state by walking the | |
346 | * stacks of sleeping tasks and looking for any to-be-patched or | |
347 | * to-be-unpatched functions. If such functions are found, the task can't be | |
348 | * switched yet. | |
349 | * | |
350 | * If any tasks are still stuck in the initial patch state, schedule a retry. | |
351 | */ | |
352 | void klp_try_complete_transition(void) | |
353 | { | |
354 | unsigned int cpu; | |
355 | struct task_struct *g, *task; | |
356 | bool complete = true; | |
357 | ||
358 | WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); | |
359 | ||
360 | /* | |
361 | * If the patch can be applied or reverted immediately, skip the | |
362 | * per-task transitions. | |
363 | */ | |
364 | if (klp_transition_patch->immediate) | |
365 | goto success; | |
366 | ||
367 | /* | |
368 | * Try to switch the tasks to the target patch state by walking their | |
369 | * stacks and looking for any to-be-patched or to-be-unpatched | |
370 | * functions. If such functions are found on a stack, or if the stack | |
371 | * is deemed unreliable, the task can't be switched yet. | |
372 | * | |
373 | * Usually this will transition most (or all) of the tasks on a system | |
374 | * unless the patch includes changes to a very common function. | |
375 | */ | |
376 | read_lock(&tasklist_lock); | |
377 | for_each_process_thread(g, task) | |
378 | if (!klp_try_switch_task(task)) | |
379 | complete = false; | |
380 | read_unlock(&tasklist_lock); | |
381 | ||
382 | /* | |
383 | * Ditto for the idle "swapper" tasks. | |
384 | */ | |
385 | get_online_cpus(); | |
386 | for_each_possible_cpu(cpu) { | |
387 | task = idle_task(cpu); | |
388 | if (cpu_online(cpu)) { | |
389 | if (!klp_try_switch_task(task)) | |
390 | complete = false; | |
391 | } else if (task->patch_state != klp_target_state) { | |
392 | /* offline idle tasks can be switched immediately */ | |
393 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
394 | task->patch_state = klp_target_state; | |
395 | } | |
396 | } | |
397 | put_online_cpus(); | |
398 | ||
399 | if (!complete) { | |
400 | /* | |
401 | * Some tasks weren't able to be switched over. Try again | |
402 | * later and/or wait for other methods like kernel exit | |
403 | * switching. | |
404 | */ | |
405 | schedule_delayed_work(&klp_transition_work, | |
406 | round_jiffies_relative(HZ)); | |
407 | return; | |
408 | } | |
409 | ||
410 | success: | |
411 | pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name, | |
412 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
413 | ||
414 | /* we're done, now cleanup the data structures */ | |
415 | klp_complete_transition(); | |
416 | } | |
417 | ||
418 | /* | |
419 | * Start the transition to the specified target patch state so tasks can begin | |
420 | * switching to it. | |
421 | */ | |
422 | void klp_start_transition(void) | |
423 | { | |
424 | struct task_struct *g, *task; | |
425 | unsigned int cpu; | |
426 | ||
427 | WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); | |
428 | ||
429 | pr_notice("'%s': %s...\n", klp_transition_patch->mod->name, | |
430 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
431 | ||
432 | /* | |
433 | * If the patch can be applied or reverted immediately, skip the | |
434 | * per-task transitions. | |
435 | */ | |
436 | if (klp_transition_patch->immediate) | |
437 | return; | |
438 | ||
439 | /* | |
440 | * Mark all normal tasks as needing a patch state update. They'll | |
441 | * switch either in klp_try_complete_transition() or as they exit the | |
442 | * kernel. | |
443 | */ | |
444 | read_lock(&tasklist_lock); | |
445 | for_each_process_thread(g, task) | |
446 | if (task->patch_state != klp_target_state) | |
447 | set_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
448 | read_unlock(&tasklist_lock); | |
449 | ||
450 | /* | |
451 | * Mark all idle tasks as needing a patch state update. They'll switch | |
452 | * either in klp_try_complete_transition() or at the idle loop switch | |
453 | * point. | |
454 | */ | |
455 | for_each_possible_cpu(cpu) { | |
456 | task = idle_task(cpu); | |
457 | if (task->patch_state != klp_target_state) | |
458 | set_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
459 | } | |
460 | } | |
461 | ||
462 | /* | |
463 | * Initialize the global target patch state and all tasks to the initial patch | |
464 | * state, and initialize all function transition states to true in preparation | |
465 | * for patching or unpatching. | |
466 | */ | |
467 | void klp_init_transition(struct klp_patch *patch, int state) | |
468 | { | |
469 | struct task_struct *g, *task; | |
470 | unsigned int cpu; | |
471 | struct klp_object *obj; | |
472 | struct klp_func *func; | |
473 | int initial_state = !state; | |
474 | ||
475 | WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED); | |
476 | ||
477 | klp_transition_patch = patch; | |
478 | ||
479 | /* | |
480 | * Set the global target patch state which tasks will switch to. This | |
481 | * has no effect until the TIF_PATCH_PENDING flags get set later. | |
482 | */ | |
483 | klp_target_state = state; | |
484 | ||
485 | /* | |
486 | * If the patch can be applied or reverted immediately, skip the | |
487 | * per-task transitions. | |
488 | */ | |
489 | if (patch->immediate) | |
490 | return; | |
491 | ||
492 | /* | |
493 | * Initialize all tasks to the initial patch state to prepare them for | |
494 | * switching to the target state. | |
495 | */ | |
496 | read_lock(&tasklist_lock); | |
497 | for_each_process_thread(g, task) { | |
498 | WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); | |
499 | task->patch_state = initial_state; | |
500 | } | |
501 | read_unlock(&tasklist_lock); | |
502 | ||
503 | /* | |
504 | * Ditto for the idle "swapper" tasks. | |
505 | */ | |
506 | for_each_possible_cpu(cpu) { | |
507 | task = idle_task(cpu); | |
508 | WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); | |
509 | task->patch_state = initial_state; | |
510 | } | |
511 | ||
512 | /* | |
513 | * Enforce the order of the task->patch_state initializations and the | |
514 | * func->transition updates to ensure that klp_ftrace_handler() doesn't | |
515 | * see a func in transition with a task->patch_state of KLP_UNDEFINED. | |
516 | * | |
517 | * Also enforce the order of the klp_target_state write and future | |
518 | * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't | |
519 | * set a task->patch_state to KLP_UNDEFINED. | |
520 | */ | |
521 | smp_wmb(); | |
522 | ||
523 | /* | |
524 | * Set the func transition states so klp_ftrace_handler() will know to | |
525 | * switch to the transition logic. | |
526 | * | |
527 | * When patching, the funcs aren't yet in the func_stack and will be | |
528 | * made visible to the ftrace handler shortly by the calls to | |
529 | * klp_patch_object(). | |
530 | * | |
531 | * When unpatching, the funcs are already in the func_stack and so are | |
532 | * already visible to the ftrace handler. | |
533 | */ | |
534 | klp_for_each_object(patch, obj) | |
535 | klp_for_each_func(obj, func) | |
536 | func->transition = true; | |
537 | } | |
538 | ||
539 | /* | |
540 | * This function can be called in the middle of an existing transition to | |
541 | * reverse the direction of the target patch state. This can be done to | |
542 | * effectively cancel an existing enable or disable operation if there are any | |
543 | * tasks which are stuck in the initial patch state. | |
544 | */ | |
545 | void klp_reverse_transition(void) | |
546 | { | |
547 | unsigned int cpu; | |
548 | struct task_struct *g, *task; | |
549 | ||
550 | klp_transition_patch->enabled = !klp_transition_patch->enabled; | |
551 | ||
552 | klp_target_state = !klp_target_state; | |
553 | ||
554 | /* | |
555 | * Clear all TIF_PATCH_PENDING flags to prevent races caused by | |
556 | * klp_update_patch_state() running in parallel with | |
557 | * klp_start_transition(). | |
558 | */ | |
559 | read_lock(&tasklist_lock); | |
560 | for_each_process_thread(g, task) | |
561 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
562 | read_unlock(&tasklist_lock); | |
563 | ||
564 | for_each_possible_cpu(cpu) | |
565 | clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING); | |
566 | ||
567 | /* Let any remaining calls to klp_update_patch_state() complete */ | |
842c0884 | 568 | klp_synchronize_transition(); |
d83a7cb3 JP |
569 | |
570 | klp_start_transition(); | |
571 | } | |
572 | ||
573 | /* Called from copy_process() during fork */ | |
574 | void klp_copy_process(struct task_struct *child) | |
575 | { | |
576 | child->patch_state = current->patch_state; | |
577 | ||
578 | /* TIF_PATCH_PENDING gets copied in setup_thread_stack() */ | |
579 | } |