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1ccea77e | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
d83a7cb3 JP |
2 | /* |
3 | * transition.c - Kernel Live Patching transition functions | |
4 | * | |
5 | * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com> | |
d83a7cb3 JP |
6 | */ |
7 | ||
8 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt | |
9 | ||
10 | #include <linux/cpu.h> | |
11 | #include <linux/stacktrace.h> | |
10517429 | 12 | #include "core.h" |
d83a7cb3 JP |
13 | #include "patch.h" |
14 | #include "transition.h" | |
d83a7cb3 JP |
15 | |
16 | #define MAX_STACK_ENTRIES 100 | |
e92606fa JP |
17 | DEFINE_PER_CPU(unsigned long[MAX_STACK_ENTRIES], klp_stack_entries); |
18 | ||
d83a7cb3 JP |
19 | #define STACK_ERR_BUF_SIZE 128 |
20 | ||
cba82dea MB |
21 | #define SIGNALS_TIMEOUT 15 |
22 | ||
d83a7cb3 JP |
23 | struct klp_patch *klp_transition_patch; |
24 | ||
25 | static int klp_target_state = KLP_UNDEFINED; | |
26 | ||
cba82dea MB |
27 | static unsigned int klp_signals_cnt; |
28 | ||
d83a7cb3 JP |
29 | /* |
30 | * This work can be performed periodically to finish patching or unpatching any | |
31 | * "straggler" tasks which failed to transition in the first attempt. | |
32 | */ | |
33 | static void klp_transition_work_fn(struct work_struct *work) | |
34 | { | |
35 | mutex_lock(&klp_mutex); | |
36 | ||
37 | if (klp_transition_patch) | |
38 | klp_try_complete_transition(); | |
39 | ||
40 | mutex_unlock(&klp_mutex); | |
41 | } | |
42 | static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn); | |
43 | ||
842c0884 PM |
44 | /* |
45 | * This function is just a stub to implement a hard force | |
6932689e | 46 | * of synchronize_rcu(). This requires synchronizing |
842c0884 PM |
47 | * tasks even in userspace and idle. |
48 | */ | |
49 | static void klp_sync(struct work_struct *work) | |
50 | { | |
51 | } | |
52 | ||
53 | /* | |
54 | * We allow to patch also functions where RCU is not watching, | |
55 | * e.g. before user_exit(). We can not rely on the RCU infrastructure | |
56 | * to do the synchronization. Instead hard force the sched synchronization. | |
57 | * | |
58 | * This approach allows to use RCU functions for manipulating func_stack | |
59 | * safely. | |
60 | */ | |
61 | static void klp_synchronize_transition(void) | |
62 | { | |
63 | schedule_on_each_cpu(klp_sync); | |
64 | } | |
65 | ||
d83a7cb3 JP |
66 | /* |
67 | * The transition to the target patch state is complete. Clean up the data | |
68 | * structures. | |
69 | */ | |
70 | static void klp_complete_transition(void) | |
71 | { | |
72 | struct klp_object *obj; | |
73 | struct klp_func *func; | |
74 | struct task_struct *g, *task; | |
75 | unsigned int cpu; | |
76 | ||
af026796 JL |
77 | pr_debug("'%s': completing %s transition\n", |
78 | klp_transition_patch->mod->name, | |
79 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
80 | ||
d697bad5 | 81 | if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) { |
7e35e4eb | 82 | klp_unpatch_replaced_patches(klp_transition_patch); |
d697bad5 PM |
83 | klp_discard_nops(klp_transition_patch); |
84 | } | |
e1452b60 | 85 | |
d83a7cb3 JP |
86 | if (klp_target_state == KLP_UNPATCHED) { |
87 | /* | |
88 | * All tasks have transitioned to KLP_UNPATCHED so we can now | |
89 | * remove the new functions from the func_stack. | |
90 | */ | |
91 | klp_unpatch_objects(klp_transition_patch); | |
92 | ||
93 | /* | |
94 | * Make sure klp_ftrace_handler() can no longer see functions | |
95 | * from this patch on the ops->func_stack. Otherwise, after | |
96 | * func->transition gets cleared, the handler may choose a | |
97 | * removed function. | |
98 | */ | |
842c0884 | 99 | klp_synchronize_transition(); |
d83a7cb3 JP |
100 | } |
101 | ||
d0807da7 MB |
102 | klp_for_each_object(klp_transition_patch, obj) |
103 | klp_for_each_func(obj, func) | |
d83a7cb3 | 104 | func->transition = false; |
3ec24776 | 105 | |
d83a7cb3 JP |
106 | /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ |
107 | if (klp_target_state == KLP_PATCHED) | |
842c0884 | 108 | klp_synchronize_transition(); |
d83a7cb3 JP |
109 | |
110 | read_lock(&tasklist_lock); | |
111 | for_each_process_thread(g, task) { | |
112 | WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); | |
113 | task->patch_state = KLP_UNDEFINED; | |
114 | } | |
115 | read_unlock(&tasklist_lock); | |
116 | ||
117 | for_each_possible_cpu(cpu) { | |
118 | task = idle_task(cpu); | |
119 | WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); | |
120 | task->patch_state = KLP_UNDEFINED; | |
121 | } | |
122 | ||
93862e38 JL |
123 | klp_for_each_object(klp_transition_patch, obj) { |
124 | if (!klp_is_object_loaded(obj)) | |
125 | continue; | |
126 | if (klp_target_state == KLP_PATCHED) | |
127 | klp_post_patch_callback(obj); | |
128 | else if (klp_target_state == KLP_UNPATCHED) | |
129 | klp_post_unpatch_callback(obj); | |
130 | } | |
131 | ||
6116c303 JL |
132 | pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name, |
133 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
134 | ||
d83a7cb3 JP |
135 | klp_target_state = KLP_UNDEFINED; |
136 | klp_transition_patch = NULL; | |
137 | } | |
138 | ||
139 | /* | |
140 | * This is called in the error path, to cancel a transition before it has | |
141 | * started, i.e. klp_init_transition() has been called but | |
142 | * klp_start_transition() hasn't. If the transition *has* been started, | |
143 | * klp_reverse_transition() should be used instead. | |
144 | */ | |
145 | void klp_cancel_transition(void) | |
146 | { | |
3ec24776 JP |
147 | if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED)) |
148 | return; | |
149 | ||
af026796 JL |
150 | pr_debug("'%s': canceling patching transition, going to unpatch\n", |
151 | klp_transition_patch->mod->name); | |
152 | ||
3ec24776 | 153 | klp_target_state = KLP_UNPATCHED; |
d83a7cb3 JP |
154 | klp_complete_transition(); |
155 | } | |
156 | ||
157 | /* | |
158 | * Switch the patched state of the task to the set of functions in the target | |
159 | * patch state. | |
160 | * | |
161 | * NOTE: If task is not 'current', the caller must ensure the task is inactive. | |
162 | * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value. | |
163 | */ | |
164 | void klp_update_patch_state(struct task_struct *task) | |
165 | { | |
842c0884 | 166 | /* |
6932689e | 167 | * A variant of synchronize_rcu() is used to allow patching functions |
842c0884 PM |
168 | * where RCU is not watching, see klp_synchronize_transition(). |
169 | */ | |
170 | preempt_disable_notrace(); | |
d83a7cb3 JP |
171 | |
172 | /* | |
173 | * This test_and_clear_tsk_thread_flag() call also serves as a read | |
174 | * barrier (smp_rmb) for two cases: | |
175 | * | |
176 | * 1) Enforce the order of the TIF_PATCH_PENDING read and the | |
177 | * klp_target_state read. The corresponding write barrier is in | |
178 | * klp_init_transition(). | |
179 | * | |
180 | * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read | |
181 | * of func->transition, if klp_ftrace_handler() is called later on | |
182 | * the same CPU. See __klp_disable_patch(). | |
183 | */ | |
184 | if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING)) | |
185 | task->patch_state = READ_ONCE(klp_target_state); | |
186 | ||
842c0884 | 187 | preempt_enable_notrace(); |
d83a7cb3 JP |
188 | } |
189 | ||
190 | /* | |
191 | * Determine whether the given stack trace includes any references to a | |
192 | * to-be-patched or to-be-unpatched function. | |
193 | */ | |
25e39e32 TG |
194 | static int klp_check_stack_func(struct klp_func *func, unsigned long *entries, |
195 | unsigned int nr_entries) | |
d83a7cb3 JP |
196 | { |
197 | unsigned long func_addr, func_size, address; | |
198 | struct klp_ops *ops; | |
199 | int i; | |
200 | ||
53910ef7 ZL |
201 | if (klp_target_state == KLP_UNPATCHED) { |
202 | /* | |
203 | * Check for the to-be-unpatched function | |
204 | * (the func itself). | |
205 | */ | |
206 | func_addr = (unsigned long)func->new_func; | |
207 | func_size = func->new_size; | |
208 | } else { | |
209 | /* | |
210 | * Check for the to-be-patched function | |
211 | * (the previous func). | |
212 | */ | |
213 | ops = klp_find_ops(func->old_func); | |
d83a7cb3 | 214 | |
53910ef7 ZL |
215 | if (list_is_singular(&ops->func_stack)) { |
216 | /* original function */ | |
217 | func_addr = (unsigned long)func->old_func; | |
218 | func_size = func->old_size; | |
d83a7cb3 | 219 | } else { |
53910ef7 ZL |
220 | /* previously patched function */ |
221 | struct klp_func *prev; | |
222 | ||
223 | prev = list_next_entry(func, stack_node); | |
224 | func_addr = (unsigned long)prev->new_func; | |
225 | func_size = prev->new_size; | |
d83a7cb3 | 226 | } |
53910ef7 ZL |
227 | } |
228 | ||
229 | for (i = 0; i < nr_entries; i++) { | |
230 | address = entries[i]; | |
d83a7cb3 JP |
231 | |
232 | if (address >= func_addr && address < func_addr + func_size) | |
233 | return -EAGAIN; | |
234 | } | |
235 | ||
236 | return 0; | |
237 | } | |
238 | ||
239 | /* | |
240 | * Determine whether it's safe to transition the task to the target patch state | |
241 | * by looking for any to-be-patched or to-be-unpatched functions on its stack. | |
242 | */ | |
00619f7c | 243 | static int klp_check_stack(struct task_struct *task, const char **oldname) |
d83a7cb3 | 244 | { |
e92606fa | 245 | unsigned long *entries = this_cpu_ptr(klp_stack_entries); |
d83a7cb3 JP |
246 | struct klp_object *obj; |
247 | struct klp_func *func; | |
25e39e32 | 248 | int ret, nr_entries; |
d83a7cb3 | 249 | |
e92606fa JP |
250 | /* Protect 'klp_stack_entries' */ |
251 | lockdep_assert_preemption_disabled(); | |
252 | ||
253 | ret = stack_trace_save_tsk_reliable(task, entries, MAX_STACK_ENTRIES); | |
00619f7c PZ |
254 | if (ret < 0) |
255 | return -EINVAL; | |
25e39e32 | 256 | nr_entries = ret; |
d83a7cb3 JP |
257 | |
258 | klp_for_each_object(klp_transition_patch, obj) { | |
259 | if (!obj->patched) | |
260 | continue; | |
261 | klp_for_each_func(obj, func) { | |
25e39e32 | 262 | ret = klp_check_stack_func(func, entries, nr_entries); |
d83a7cb3 | 263 | if (ret) { |
00619f7c PZ |
264 | *oldname = func->old_name; |
265 | return -EADDRINUSE; | |
d83a7cb3 JP |
266 | } |
267 | } | |
268 | } | |
269 | ||
270 | return 0; | |
271 | } | |
272 | ||
00619f7c PZ |
273 | static int klp_check_and_switch_task(struct task_struct *task, void *arg) |
274 | { | |
275 | int ret; | |
276 | ||
277 | if (task_curr(task) && task != current) | |
278 | return -EBUSY; | |
279 | ||
280 | ret = klp_check_stack(task, arg); | |
281 | if (ret) | |
282 | return ret; | |
283 | ||
284 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
285 | task->patch_state = klp_target_state; | |
286 | return 0; | |
287 | } | |
288 | ||
d83a7cb3 JP |
289 | /* |
290 | * Try to safely switch a task to the target patch state. If it's currently | |
291 | * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or | |
292 | * if the stack is unreliable, return false. | |
293 | */ | |
294 | static bool klp_try_switch_task(struct task_struct *task) | |
295 | { | |
00619f7c | 296 | const char *old_name; |
d83a7cb3 | 297 | int ret; |
d83a7cb3 JP |
298 | |
299 | /* check if this task has already switched over */ | |
300 | if (task->patch_state == klp_target_state) | |
301 | return true; | |
302 | ||
67059d65 MB |
303 | /* |
304 | * For arches which don't have reliable stack traces, we have to rely | |
305 | * on other methods (e.g., switching tasks at kernel exit). | |
306 | */ | |
307 | if (!klp_have_reliable_stack()) | |
308 | return false; | |
309 | ||
d83a7cb3 JP |
310 | /* |
311 | * Now try to check the stack for any to-be-patched or to-be-unpatched | |
312 | * functions. If all goes well, switch the task to the target patch | |
313 | * state. | |
314 | */ | |
383439d3 JP |
315 | if (task == current) |
316 | ret = klp_check_and_switch_task(current, &old_name); | |
317 | else | |
318 | ret = task_call_func(task, klp_check_and_switch_task, &old_name); | |
319 | ||
00619f7c PZ |
320 | switch (ret) { |
321 | case 0: /* success */ | |
322 | break; | |
d83a7cb3 | 323 | |
00619f7c PZ |
324 | case -EBUSY: /* klp_check_and_switch_task() */ |
325 | pr_debug("%s: %s:%d is running\n", | |
326 | __func__, task->comm, task->pid); | |
327 | break; | |
328 | case -EINVAL: /* klp_check_and_switch_task() */ | |
329 | pr_debug("%s: %s:%d has an unreliable stack\n", | |
330 | __func__, task->comm, task->pid); | |
331 | break; | |
332 | case -EADDRINUSE: /* klp_check_and_switch_task() */ | |
333 | pr_debug("%s: %s:%d is sleeping on function %s\n", | |
334 | __func__, task->comm, task->pid, old_name); | |
335 | break; | |
336 | ||
337 | default: | |
338 | pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n", | |
339 | __func__, ret, task->comm, task->pid); | |
340 | break; | |
d83a7cb3 JP |
341 | } |
342 | ||
00619f7c | 343 | return !ret; |
d83a7cb3 JP |
344 | } |
345 | ||
0b3d5279 MB |
346 | /* |
347 | * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. | |
348 | * Kthreads with TIF_PATCH_PENDING set are woken up. | |
349 | */ | |
350 | static void klp_send_signals(void) | |
351 | { | |
352 | struct task_struct *g, *task; | |
353 | ||
354 | if (klp_signals_cnt == SIGNALS_TIMEOUT) | |
355 | pr_notice("signaling remaining tasks\n"); | |
356 | ||
357 | read_lock(&tasklist_lock); | |
358 | for_each_process_thread(g, task) { | |
359 | if (!klp_patch_pending(task)) | |
360 | continue; | |
361 | ||
362 | /* | |
363 | * There is a small race here. We could see TIF_PATCH_PENDING | |
364 | * set and decide to wake up a kthread or send a fake signal. | |
365 | * Meanwhile the task could migrate itself and the action | |
366 | * would be meaningless. It is not serious though. | |
367 | */ | |
368 | if (task->flags & PF_KTHREAD) { | |
369 | /* | |
370 | * Wake up a kthread which sleeps interruptedly and | |
371 | * still has not been migrated. | |
372 | */ | |
373 | wake_up_state(task, TASK_INTERRUPTIBLE); | |
374 | } else { | |
375 | /* | |
376 | * Send fake signal to all non-kthread tasks which are | |
377 | * still not migrated. | |
378 | */ | |
8df1947c | 379 | set_notify_signal(task); |
0b3d5279 MB |
380 | } |
381 | } | |
382 | read_unlock(&tasklist_lock); | |
383 | } | |
384 | ||
d83a7cb3 JP |
385 | /* |
386 | * Try to switch all remaining tasks to the target patch state by walking the | |
387 | * stacks of sleeping tasks and looking for any to-be-patched or | |
388 | * to-be-unpatched functions. If such functions are found, the task can't be | |
389 | * switched yet. | |
390 | * | |
391 | * If any tasks are still stuck in the initial patch state, schedule a retry. | |
392 | */ | |
393 | void klp_try_complete_transition(void) | |
394 | { | |
395 | unsigned int cpu; | |
396 | struct task_struct *g, *task; | |
958ef1e3 | 397 | struct klp_patch *patch; |
d83a7cb3 JP |
398 | bool complete = true; |
399 | ||
400 | WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); | |
401 | ||
d83a7cb3 JP |
402 | /* |
403 | * Try to switch the tasks to the target patch state by walking their | |
404 | * stacks and looking for any to-be-patched or to-be-unpatched | |
405 | * functions. If such functions are found on a stack, or if the stack | |
406 | * is deemed unreliable, the task can't be switched yet. | |
407 | * | |
408 | * Usually this will transition most (or all) of the tasks on a system | |
409 | * unless the patch includes changes to a very common function. | |
410 | */ | |
411 | read_lock(&tasklist_lock); | |
412 | for_each_process_thread(g, task) | |
413 | if (!klp_try_switch_task(task)) | |
414 | complete = false; | |
415 | read_unlock(&tasklist_lock); | |
416 | ||
417 | /* | |
418 | * Ditto for the idle "swapper" tasks. | |
419 | */ | |
1daf08a0 | 420 | cpus_read_lock(); |
d83a7cb3 JP |
421 | for_each_possible_cpu(cpu) { |
422 | task = idle_task(cpu); | |
423 | if (cpu_online(cpu)) { | |
5de62ea8 | 424 | if (!klp_try_switch_task(task)) { |
d83a7cb3 | 425 | complete = false; |
5de62ea8 PZ |
426 | /* Make idle task go through the main loop. */ |
427 | wake_up_if_idle(cpu); | |
428 | } | |
d83a7cb3 JP |
429 | } else if (task->patch_state != klp_target_state) { |
430 | /* offline idle tasks can be switched immediately */ | |
431 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
432 | task->patch_state = klp_target_state; | |
433 | } | |
434 | } | |
1daf08a0 | 435 | cpus_read_unlock(); |
d83a7cb3 JP |
436 | |
437 | if (!complete) { | |
cba82dea MB |
438 | if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT)) |
439 | klp_send_signals(); | |
440 | klp_signals_cnt++; | |
441 | ||
d83a7cb3 JP |
442 | /* |
443 | * Some tasks weren't able to be switched over. Try again | |
444 | * later and/or wait for other methods like kernel exit | |
445 | * switching. | |
446 | */ | |
447 | schedule_delayed_work(&klp_transition_work, | |
448 | round_jiffies_relative(HZ)); | |
449 | return; | |
450 | } | |
451 | ||
d83a7cb3 | 452 | /* we're done, now cleanup the data structures */ |
958ef1e3 | 453 | patch = klp_transition_patch; |
d83a7cb3 | 454 | klp_complete_transition(); |
958ef1e3 PM |
455 | |
456 | /* | |
7e35e4eb | 457 | * It would make more sense to free the unused patches in |
958ef1e3 PM |
458 | * klp_complete_transition() but it is called also |
459 | * from klp_cancel_transition(). | |
460 | */ | |
7e35e4eb PM |
461 | if (!patch->enabled) |
462 | klp_free_patch_async(patch); | |
463 | else if (patch->replace) | |
464 | klp_free_replaced_patches_async(patch); | |
d83a7cb3 JP |
465 | } |
466 | ||
467 | /* | |
468 | * Start the transition to the specified target patch state so tasks can begin | |
469 | * switching to it. | |
470 | */ | |
471 | void klp_start_transition(void) | |
472 | { | |
473 | struct task_struct *g, *task; | |
474 | unsigned int cpu; | |
475 | ||
476 | WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); | |
477 | ||
af026796 JL |
478 | pr_notice("'%s': starting %s transition\n", |
479 | klp_transition_patch->mod->name, | |
d83a7cb3 JP |
480 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); |
481 | ||
d83a7cb3 JP |
482 | /* |
483 | * Mark all normal tasks as needing a patch state update. They'll | |
484 | * switch either in klp_try_complete_transition() or as they exit the | |
485 | * kernel. | |
486 | */ | |
487 | read_lock(&tasklist_lock); | |
488 | for_each_process_thread(g, task) | |
489 | if (task->patch_state != klp_target_state) | |
490 | set_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
491 | read_unlock(&tasklist_lock); | |
492 | ||
493 | /* | |
494 | * Mark all idle tasks as needing a patch state update. They'll switch | |
495 | * either in klp_try_complete_transition() or at the idle loop switch | |
496 | * point. | |
497 | */ | |
498 | for_each_possible_cpu(cpu) { | |
499 | task = idle_task(cpu); | |
500 | if (task->patch_state != klp_target_state) | |
501 | set_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
502 | } | |
cba82dea MB |
503 | |
504 | klp_signals_cnt = 0; | |
d83a7cb3 JP |
505 | } |
506 | ||
507 | /* | |
508 | * Initialize the global target patch state and all tasks to the initial patch | |
509 | * state, and initialize all function transition states to true in preparation | |
510 | * for patching or unpatching. | |
511 | */ | |
512 | void klp_init_transition(struct klp_patch *patch, int state) | |
513 | { | |
514 | struct task_struct *g, *task; | |
515 | unsigned int cpu; | |
516 | struct klp_object *obj; | |
517 | struct klp_func *func; | |
518 | int initial_state = !state; | |
519 | ||
520 | WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED); | |
521 | ||
522 | klp_transition_patch = patch; | |
523 | ||
524 | /* | |
525 | * Set the global target patch state which tasks will switch to. This | |
526 | * has no effect until the TIF_PATCH_PENDING flags get set later. | |
527 | */ | |
528 | klp_target_state = state; | |
529 | ||
af026796 JL |
530 | pr_debug("'%s': initializing %s transition\n", patch->mod->name, |
531 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
532 | ||
d83a7cb3 JP |
533 | /* |
534 | * Initialize all tasks to the initial patch state to prepare them for | |
535 | * switching to the target state. | |
536 | */ | |
537 | read_lock(&tasklist_lock); | |
538 | for_each_process_thread(g, task) { | |
539 | WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); | |
540 | task->patch_state = initial_state; | |
541 | } | |
542 | read_unlock(&tasklist_lock); | |
543 | ||
544 | /* | |
545 | * Ditto for the idle "swapper" tasks. | |
546 | */ | |
547 | for_each_possible_cpu(cpu) { | |
548 | task = idle_task(cpu); | |
549 | WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); | |
550 | task->patch_state = initial_state; | |
551 | } | |
552 | ||
553 | /* | |
554 | * Enforce the order of the task->patch_state initializations and the | |
555 | * func->transition updates to ensure that klp_ftrace_handler() doesn't | |
556 | * see a func in transition with a task->patch_state of KLP_UNDEFINED. | |
557 | * | |
558 | * Also enforce the order of the klp_target_state write and future | |
559 | * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't | |
560 | * set a task->patch_state to KLP_UNDEFINED. | |
561 | */ | |
562 | smp_wmb(); | |
563 | ||
564 | /* | |
565 | * Set the func transition states so klp_ftrace_handler() will know to | |
566 | * switch to the transition logic. | |
567 | * | |
568 | * When patching, the funcs aren't yet in the func_stack and will be | |
569 | * made visible to the ftrace handler shortly by the calls to | |
570 | * klp_patch_object(). | |
571 | * | |
572 | * When unpatching, the funcs are already in the func_stack and so are | |
573 | * already visible to the ftrace handler. | |
574 | */ | |
575 | klp_for_each_object(patch, obj) | |
576 | klp_for_each_func(obj, func) | |
577 | func->transition = true; | |
578 | } | |
579 | ||
580 | /* | |
581 | * This function can be called in the middle of an existing transition to | |
582 | * reverse the direction of the target patch state. This can be done to | |
583 | * effectively cancel an existing enable or disable operation if there are any | |
584 | * tasks which are stuck in the initial patch state. | |
585 | */ | |
586 | void klp_reverse_transition(void) | |
587 | { | |
588 | unsigned int cpu; | |
589 | struct task_struct *g, *task; | |
590 | ||
af026796 JL |
591 | pr_debug("'%s': reversing transition from %s\n", |
592 | klp_transition_patch->mod->name, | |
593 | klp_target_state == KLP_PATCHED ? "patching to unpatching" : | |
594 | "unpatching to patching"); | |
595 | ||
d83a7cb3 JP |
596 | klp_transition_patch->enabled = !klp_transition_patch->enabled; |
597 | ||
598 | klp_target_state = !klp_target_state; | |
599 | ||
600 | /* | |
601 | * Clear all TIF_PATCH_PENDING flags to prevent races caused by | |
602 | * klp_update_patch_state() running in parallel with | |
603 | * klp_start_transition(). | |
604 | */ | |
605 | read_lock(&tasklist_lock); | |
606 | for_each_process_thread(g, task) | |
607 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
608 | read_unlock(&tasklist_lock); | |
609 | ||
610 | for_each_possible_cpu(cpu) | |
611 | clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING); | |
612 | ||
613 | /* Let any remaining calls to klp_update_patch_state() complete */ | |
842c0884 | 614 | klp_synchronize_transition(); |
d83a7cb3 JP |
615 | |
616 | klp_start_transition(); | |
617 | } | |
618 | ||
619 | /* Called from copy_process() during fork */ | |
620 | void klp_copy_process(struct task_struct *child) | |
621 | { | |
d83a7cb3 | 622 | |
747f7a29 RR |
623 | /* |
624 | * The parent process may have gone through a KLP transition since | |
625 | * the thread flag was copied in setup_thread_stack earlier. Bring | |
626 | * the task flag up to date with the parent here. | |
627 | * | |
628 | * The operation is serialized against all klp_*_transition() | |
629 | * operations by the tasklist_lock. The only exception is | |
630 | * klp_update_patch_state(current), but we cannot race with | |
631 | * that because we are current. | |
632 | */ | |
633 | if (test_tsk_thread_flag(current, TIF_PATCH_PENDING)) | |
634 | set_tsk_thread_flag(child, TIF_PATCH_PENDING); | |
635 | else | |
636 | clear_tsk_thread_flag(child, TIF_PATCH_PENDING); | |
637 | ||
638 | child->patch_state = current->patch_state; | |
d83a7cb3 | 639 | } |
43347d56 | 640 | |
c99a2be7 MB |
641 | /* |
642 | * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an | |
643 | * existing transition to finish. | |
644 | * | |
645 | * NOTE: klp_update_patch_state(task) requires the task to be inactive or | |
646 | * 'current'. This is not the case here and the consistency model could be | |
647 | * broken. Administrator, who is the only one to execute the | |
648 | * klp_force_transitions(), has to be aware of this. | |
649 | */ | |
650 | void klp_force_transition(void) | |
651 | { | |
68007289 | 652 | struct klp_patch *patch; |
c99a2be7 MB |
653 | struct task_struct *g, *task; |
654 | unsigned int cpu; | |
655 | ||
656 | pr_warn("forcing remaining tasks to the patched state\n"); | |
657 | ||
658 | read_lock(&tasklist_lock); | |
659 | for_each_process_thread(g, task) | |
660 | klp_update_patch_state(task); | |
661 | read_unlock(&tasklist_lock); | |
662 | ||
663 | for_each_possible_cpu(cpu) | |
664 | klp_update_patch_state(idle_task(cpu)); | |
665 | ||
29573083 CZ |
666 | /* Set forced flag for patches being removed. */ |
667 | if (klp_target_state == KLP_UNPATCHED) | |
668 | klp_transition_patch->forced = true; | |
669 | else if (klp_transition_patch->replace) { | |
670 | klp_for_each_patch(patch) { | |
671 | if (patch != klp_transition_patch) | |
672 | patch->forced = true; | |
673 | } | |
674 | } | |
c99a2be7 | 675 | } |