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