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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> | |
e3ff7c60 | 12 | #include <linux/static_call.h> |
10517429 | 13 | #include "core.h" |
d83a7cb3 JP |
14 | #include "patch.h" |
15 | #include "transition.h" | |
d83a7cb3 JP |
16 | |
17 | #define MAX_STACK_ENTRIES 100 | |
42cffe98 | 18 | static DEFINE_PER_CPU(unsigned long[MAX_STACK_ENTRIES], klp_stack_entries); |
e92606fa | 19 | |
d83a7cb3 JP |
20 | #define STACK_ERR_BUF_SIZE 128 |
21 | ||
cba82dea MB |
22 | #define SIGNALS_TIMEOUT 15 |
23 | ||
d83a7cb3 JP |
24 | struct klp_patch *klp_transition_patch; |
25 | ||
26 | static int klp_target_state = KLP_UNDEFINED; | |
27 | ||
cba82dea MB |
28 | static unsigned int klp_signals_cnt; |
29 | ||
e3ff7c60 JP |
30 | /* |
31 | * When a livepatch is in progress, enable klp stack checking in | |
32 | * cond_resched(). This helps CPU-bound kthreads get patched. | |
33 | */ | |
34 | #if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) | |
35 | ||
36 | #define klp_cond_resched_enable() sched_dynamic_klp_enable() | |
37 | #define klp_cond_resched_disable() sched_dynamic_klp_disable() | |
38 | ||
39 | #else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */ | |
40 | ||
41 | DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key); | |
42 | EXPORT_SYMBOL(klp_sched_try_switch_key); | |
43 | ||
44 | #define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key) | |
45 | #define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key) | |
46 | ||
47 | #endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */ | |
48 | ||
d83a7cb3 JP |
49 | /* |
50 | * This work can be performed periodically to finish patching or unpatching any | |
51 | * "straggler" tasks which failed to transition in the first attempt. | |
52 | */ | |
53 | static void klp_transition_work_fn(struct work_struct *work) | |
54 | { | |
55 | mutex_lock(&klp_mutex); | |
56 | ||
57 | if (klp_transition_patch) | |
58 | klp_try_complete_transition(); | |
59 | ||
60 | mutex_unlock(&klp_mutex); | |
61 | } | |
62 | static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn); | |
63 | ||
842c0884 PM |
64 | /* |
65 | * This function is just a stub to implement a hard force | |
6932689e | 66 | * of synchronize_rcu(). This requires synchronizing |
842c0884 PM |
67 | * tasks even in userspace and idle. |
68 | */ | |
69 | static void klp_sync(struct work_struct *work) | |
70 | { | |
71 | } | |
72 | ||
73 | /* | |
74 | * We allow to patch also functions where RCU is not watching, | |
75 | * e.g. before user_exit(). We can not rely on the RCU infrastructure | |
76 | * to do the synchronization. Instead hard force the sched synchronization. | |
77 | * | |
78 | * This approach allows to use RCU functions for manipulating func_stack | |
79 | * safely. | |
80 | */ | |
81 | static void klp_synchronize_transition(void) | |
82 | { | |
83 | schedule_on_each_cpu(klp_sync); | |
84 | } | |
85 | ||
d83a7cb3 JP |
86 | /* |
87 | * The transition to the target patch state is complete. Clean up the data | |
88 | * structures. | |
89 | */ | |
90 | static void klp_complete_transition(void) | |
91 | { | |
92 | struct klp_object *obj; | |
93 | struct klp_func *func; | |
94 | struct task_struct *g, *task; | |
95 | unsigned int cpu; | |
96 | ||
af026796 JL |
97 | pr_debug("'%s': completing %s transition\n", |
98 | klp_transition_patch->mod->name, | |
99 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
100 | ||
d697bad5 | 101 | if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) { |
7e35e4eb | 102 | klp_unpatch_replaced_patches(klp_transition_patch); |
d697bad5 PM |
103 | klp_discard_nops(klp_transition_patch); |
104 | } | |
e1452b60 | 105 | |
d83a7cb3 JP |
106 | if (klp_target_state == KLP_UNPATCHED) { |
107 | /* | |
108 | * All tasks have transitioned to KLP_UNPATCHED so we can now | |
109 | * remove the new functions from the func_stack. | |
110 | */ | |
111 | klp_unpatch_objects(klp_transition_patch); | |
112 | ||
113 | /* | |
114 | * Make sure klp_ftrace_handler() can no longer see functions | |
115 | * from this patch on the ops->func_stack. Otherwise, after | |
116 | * func->transition gets cleared, the handler may choose a | |
117 | * removed function. | |
118 | */ | |
842c0884 | 119 | klp_synchronize_transition(); |
d83a7cb3 JP |
120 | } |
121 | ||
d0807da7 MB |
122 | klp_for_each_object(klp_transition_patch, obj) |
123 | klp_for_each_func(obj, func) | |
d83a7cb3 | 124 | func->transition = false; |
3ec24776 | 125 | |
d83a7cb3 JP |
126 | /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ |
127 | if (klp_target_state == KLP_PATCHED) | |
842c0884 | 128 | klp_synchronize_transition(); |
d83a7cb3 JP |
129 | |
130 | read_lock(&tasklist_lock); | |
131 | for_each_process_thread(g, task) { | |
132 | WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); | |
133 | task->patch_state = KLP_UNDEFINED; | |
134 | } | |
135 | read_unlock(&tasklist_lock); | |
136 | ||
137 | for_each_possible_cpu(cpu) { | |
138 | task = idle_task(cpu); | |
139 | WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); | |
140 | task->patch_state = KLP_UNDEFINED; | |
141 | } | |
142 | ||
93862e38 JL |
143 | klp_for_each_object(klp_transition_patch, obj) { |
144 | if (!klp_is_object_loaded(obj)) | |
145 | continue; | |
146 | if (klp_target_state == KLP_PATCHED) | |
147 | klp_post_patch_callback(obj); | |
148 | else if (klp_target_state == KLP_UNPATCHED) | |
149 | klp_post_unpatch_callback(obj); | |
150 | } | |
151 | ||
6116c303 JL |
152 | pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name, |
153 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
154 | ||
d83a7cb3 JP |
155 | klp_target_state = KLP_UNDEFINED; |
156 | klp_transition_patch = NULL; | |
157 | } | |
158 | ||
159 | /* | |
160 | * This is called in the error path, to cancel a transition before it has | |
161 | * started, i.e. klp_init_transition() has been called but | |
162 | * klp_start_transition() hasn't. If the transition *has* been started, | |
163 | * klp_reverse_transition() should be used instead. | |
164 | */ | |
165 | void klp_cancel_transition(void) | |
166 | { | |
3ec24776 JP |
167 | if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED)) |
168 | return; | |
169 | ||
af026796 JL |
170 | pr_debug("'%s': canceling patching transition, going to unpatch\n", |
171 | klp_transition_patch->mod->name); | |
172 | ||
3ec24776 | 173 | klp_target_state = KLP_UNPATCHED; |
d83a7cb3 JP |
174 | klp_complete_transition(); |
175 | } | |
176 | ||
177 | /* | |
178 | * Switch the patched state of the task to the set of functions in the target | |
179 | * patch state. | |
180 | * | |
181 | * NOTE: If task is not 'current', the caller must ensure the task is inactive. | |
182 | * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value. | |
183 | */ | |
184 | void klp_update_patch_state(struct task_struct *task) | |
185 | { | |
842c0884 | 186 | /* |
6932689e | 187 | * A variant of synchronize_rcu() is used to allow patching functions |
842c0884 PM |
188 | * where RCU is not watching, see klp_synchronize_transition(). |
189 | */ | |
190 | preempt_disable_notrace(); | |
d83a7cb3 JP |
191 | |
192 | /* | |
193 | * This test_and_clear_tsk_thread_flag() call also serves as a read | |
194 | * barrier (smp_rmb) for two cases: | |
195 | * | |
196 | * 1) Enforce the order of the TIF_PATCH_PENDING read and the | |
e3ff7c60 JP |
197 | * klp_target_state read. The corresponding write barriers are in |
198 | * klp_init_transition() and klp_reverse_transition(). | |
d83a7cb3 JP |
199 | * |
200 | * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read | |
201 | * of func->transition, if klp_ftrace_handler() is called later on | |
202 | * the same CPU. See __klp_disable_patch(). | |
203 | */ | |
204 | if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING)) | |
205 | task->patch_state = READ_ONCE(klp_target_state); | |
206 | ||
842c0884 | 207 | preempt_enable_notrace(); |
d83a7cb3 JP |
208 | } |
209 | ||
210 | /* | |
211 | * Determine whether the given stack trace includes any references to a | |
212 | * to-be-patched or to-be-unpatched function. | |
213 | */ | |
25e39e32 TG |
214 | static int klp_check_stack_func(struct klp_func *func, unsigned long *entries, |
215 | unsigned int nr_entries) | |
d83a7cb3 JP |
216 | { |
217 | unsigned long func_addr, func_size, address; | |
218 | struct klp_ops *ops; | |
219 | int i; | |
220 | ||
53910ef7 ZL |
221 | if (klp_target_state == KLP_UNPATCHED) { |
222 | /* | |
223 | * Check for the to-be-unpatched function | |
224 | * (the func itself). | |
225 | */ | |
226 | func_addr = (unsigned long)func->new_func; | |
227 | func_size = func->new_size; | |
228 | } else { | |
229 | /* | |
230 | * Check for the to-be-patched function | |
231 | * (the previous func). | |
232 | */ | |
233 | ops = klp_find_ops(func->old_func); | |
d83a7cb3 | 234 | |
53910ef7 ZL |
235 | if (list_is_singular(&ops->func_stack)) { |
236 | /* original function */ | |
237 | func_addr = (unsigned long)func->old_func; | |
238 | func_size = func->old_size; | |
d83a7cb3 | 239 | } else { |
53910ef7 ZL |
240 | /* previously patched function */ |
241 | struct klp_func *prev; | |
242 | ||
243 | prev = list_next_entry(func, stack_node); | |
244 | func_addr = (unsigned long)prev->new_func; | |
245 | func_size = prev->new_size; | |
d83a7cb3 | 246 | } |
53910ef7 ZL |
247 | } |
248 | ||
249 | for (i = 0; i < nr_entries; i++) { | |
250 | address = entries[i]; | |
d83a7cb3 JP |
251 | |
252 | if (address >= func_addr && address < func_addr + func_size) | |
253 | return -EAGAIN; | |
254 | } | |
255 | ||
256 | return 0; | |
257 | } | |
258 | ||
259 | /* | |
260 | * Determine whether it's safe to transition the task to the target patch state | |
261 | * by looking for any to-be-patched or to-be-unpatched functions on its stack. | |
262 | */ | |
00619f7c | 263 | static int klp_check_stack(struct task_struct *task, const char **oldname) |
d83a7cb3 | 264 | { |
e92606fa | 265 | unsigned long *entries = this_cpu_ptr(klp_stack_entries); |
d83a7cb3 JP |
266 | struct klp_object *obj; |
267 | struct klp_func *func; | |
25e39e32 | 268 | int ret, nr_entries; |
d83a7cb3 | 269 | |
e92606fa JP |
270 | /* Protect 'klp_stack_entries' */ |
271 | lockdep_assert_preemption_disabled(); | |
272 | ||
273 | ret = stack_trace_save_tsk_reliable(task, entries, MAX_STACK_ENTRIES); | |
00619f7c PZ |
274 | if (ret < 0) |
275 | return -EINVAL; | |
25e39e32 | 276 | nr_entries = ret; |
d83a7cb3 JP |
277 | |
278 | klp_for_each_object(klp_transition_patch, obj) { | |
279 | if (!obj->patched) | |
280 | continue; | |
281 | klp_for_each_func(obj, func) { | |
25e39e32 | 282 | ret = klp_check_stack_func(func, entries, nr_entries); |
d83a7cb3 | 283 | if (ret) { |
00619f7c PZ |
284 | *oldname = func->old_name; |
285 | return -EADDRINUSE; | |
d83a7cb3 JP |
286 | } |
287 | } | |
288 | } | |
289 | ||
290 | return 0; | |
291 | } | |
292 | ||
00619f7c PZ |
293 | static int klp_check_and_switch_task(struct task_struct *task, void *arg) |
294 | { | |
295 | int ret; | |
296 | ||
297 | if (task_curr(task) && task != current) | |
298 | return -EBUSY; | |
299 | ||
300 | ret = klp_check_stack(task, arg); | |
301 | if (ret) | |
302 | return ret; | |
303 | ||
304 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
305 | task->patch_state = klp_target_state; | |
306 | return 0; | |
307 | } | |
308 | ||
d83a7cb3 JP |
309 | /* |
310 | * Try to safely switch a task to the target patch state. If it's currently | |
311 | * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or | |
312 | * if the stack is unreliable, return false. | |
313 | */ | |
314 | static bool klp_try_switch_task(struct task_struct *task) | |
315 | { | |
00619f7c | 316 | const char *old_name; |
d83a7cb3 | 317 | int ret; |
d83a7cb3 JP |
318 | |
319 | /* check if this task has already switched over */ | |
320 | if (task->patch_state == klp_target_state) | |
321 | return true; | |
322 | ||
67059d65 MB |
323 | /* |
324 | * For arches which don't have reliable stack traces, we have to rely | |
325 | * on other methods (e.g., switching tasks at kernel exit). | |
326 | */ | |
327 | if (!klp_have_reliable_stack()) | |
328 | return false; | |
329 | ||
d83a7cb3 JP |
330 | /* |
331 | * Now try to check the stack for any to-be-patched or to-be-unpatched | |
332 | * functions. If all goes well, switch the task to the target patch | |
333 | * state. | |
334 | */ | |
383439d3 JP |
335 | if (task == current) |
336 | ret = klp_check_and_switch_task(current, &old_name); | |
337 | else | |
338 | ret = task_call_func(task, klp_check_and_switch_task, &old_name); | |
339 | ||
00619f7c PZ |
340 | switch (ret) { |
341 | case 0: /* success */ | |
342 | break; | |
d83a7cb3 | 343 | |
00619f7c PZ |
344 | case -EBUSY: /* klp_check_and_switch_task() */ |
345 | pr_debug("%s: %s:%d is running\n", | |
346 | __func__, task->comm, task->pid); | |
347 | break; | |
348 | case -EINVAL: /* klp_check_and_switch_task() */ | |
349 | pr_debug("%s: %s:%d has an unreliable stack\n", | |
350 | __func__, task->comm, task->pid); | |
351 | break; | |
352 | case -EADDRINUSE: /* klp_check_and_switch_task() */ | |
353 | pr_debug("%s: %s:%d is sleeping on function %s\n", | |
354 | __func__, task->comm, task->pid, old_name); | |
355 | break; | |
356 | ||
357 | default: | |
358 | pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n", | |
359 | __func__, ret, task->comm, task->pid); | |
360 | break; | |
d83a7cb3 JP |
361 | } |
362 | ||
00619f7c | 363 | return !ret; |
d83a7cb3 JP |
364 | } |
365 | ||
e3ff7c60 JP |
366 | void __klp_sched_try_switch(void) |
367 | { | |
368 | if (likely(!klp_patch_pending(current))) | |
369 | return; | |
370 | ||
371 | /* | |
372 | * This function is called from cond_resched() which is called in many | |
373 | * places throughout the kernel. Using the klp_mutex here might | |
374 | * deadlock. | |
375 | * | |
376 | * Instead, disable preemption to prevent racing with other callers of | |
377 | * klp_try_switch_task(). Thanks to task_call_func() they won't be | |
378 | * able to switch this task while it's running. | |
379 | */ | |
380 | preempt_disable(); | |
381 | ||
382 | /* | |
383 | * Make sure current didn't get patched between the above check and | |
384 | * preempt_disable(). | |
385 | */ | |
386 | if (unlikely(!klp_patch_pending(current))) | |
387 | goto out; | |
388 | ||
389 | /* | |
390 | * Enforce the order of the TIF_PATCH_PENDING read above and the | |
391 | * klp_target_state read in klp_try_switch_task(). The corresponding | |
392 | * write barriers are in klp_init_transition() and | |
393 | * klp_reverse_transition(). | |
394 | */ | |
395 | smp_rmb(); | |
396 | ||
397 | klp_try_switch_task(current); | |
398 | ||
399 | out: | |
400 | preempt_enable(); | |
401 | } | |
402 | EXPORT_SYMBOL(__klp_sched_try_switch); | |
403 | ||
0b3d5279 MB |
404 | /* |
405 | * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. | |
406 | * Kthreads with TIF_PATCH_PENDING set are woken up. | |
407 | */ | |
408 | static void klp_send_signals(void) | |
409 | { | |
410 | struct task_struct *g, *task; | |
411 | ||
412 | if (klp_signals_cnt == SIGNALS_TIMEOUT) | |
413 | pr_notice("signaling remaining tasks\n"); | |
414 | ||
415 | read_lock(&tasklist_lock); | |
416 | for_each_process_thread(g, task) { | |
417 | if (!klp_patch_pending(task)) | |
418 | continue; | |
419 | ||
420 | /* | |
421 | * There is a small race here. We could see TIF_PATCH_PENDING | |
422 | * set and decide to wake up a kthread or send a fake signal. | |
423 | * Meanwhile the task could migrate itself and the action | |
424 | * would be meaningless. It is not serious though. | |
425 | */ | |
426 | if (task->flags & PF_KTHREAD) { | |
427 | /* | |
428 | * Wake up a kthread which sleeps interruptedly and | |
429 | * still has not been migrated. | |
430 | */ | |
431 | wake_up_state(task, TASK_INTERRUPTIBLE); | |
432 | } else { | |
433 | /* | |
434 | * Send fake signal to all non-kthread tasks which are | |
435 | * still not migrated. | |
436 | */ | |
8df1947c | 437 | set_notify_signal(task); |
0b3d5279 MB |
438 | } |
439 | } | |
440 | read_unlock(&tasklist_lock); | |
441 | } | |
442 | ||
d83a7cb3 JP |
443 | /* |
444 | * Try to switch all remaining tasks to the target patch state by walking the | |
445 | * stacks of sleeping tasks and looking for any to-be-patched or | |
446 | * to-be-unpatched functions. If such functions are found, the task can't be | |
447 | * switched yet. | |
448 | * | |
449 | * If any tasks are still stuck in the initial patch state, schedule a retry. | |
450 | */ | |
451 | void klp_try_complete_transition(void) | |
452 | { | |
453 | unsigned int cpu; | |
454 | struct task_struct *g, *task; | |
958ef1e3 | 455 | struct klp_patch *patch; |
d83a7cb3 JP |
456 | bool complete = true; |
457 | ||
458 | WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); | |
459 | ||
d83a7cb3 JP |
460 | /* |
461 | * Try to switch the tasks to the target patch state by walking their | |
462 | * stacks and looking for any to-be-patched or to-be-unpatched | |
463 | * functions. If such functions are found on a stack, or if the stack | |
464 | * is deemed unreliable, the task can't be switched yet. | |
465 | * | |
466 | * Usually this will transition most (or all) of the tasks on a system | |
467 | * unless the patch includes changes to a very common function. | |
468 | */ | |
469 | read_lock(&tasklist_lock); | |
470 | for_each_process_thread(g, task) | |
471 | if (!klp_try_switch_task(task)) | |
472 | complete = false; | |
473 | read_unlock(&tasklist_lock); | |
474 | ||
475 | /* | |
476 | * Ditto for the idle "swapper" tasks. | |
477 | */ | |
1daf08a0 | 478 | cpus_read_lock(); |
d83a7cb3 JP |
479 | for_each_possible_cpu(cpu) { |
480 | task = idle_task(cpu); | |
481 | if (cpu_online(cpu)) { | |
5de62ea8 | 482 | if (!klp_try_switch_task(task)) { |
d83a7cb3 | 483 | complete = false; |
5de62ea8 PZ |
484 | /* Make idle task go through the main loop. */ |
485 | wake_up_if_idle(cpu); | |
486 | } | |
d83a7cb3 JP |
487 | } else if (task->patch_state != klp_target_state) { |
488 | /* offline idle tasks can be switched immediately */ | |
489 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
490 | task->patch_state = klp_target_state; | |
491 | } | |
492 | } | |
1daf08a0 | 493 | cpus_read_unlock(); |
d83a7cb3 JP |
494 | |
495 | if (!complete) { | |
cba82dea MB |
496 | if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT)) |
497 | klp_send_signals(); | |
498 | klp_signals_cnt++; | |
499 | ||
d83a7cb3 JP |
500 | /* |
501 | * Some tasks weren't able to be switched over. Try again | |
502 | * later and/or wait for other methods like kernel exit | |
503 | * switching. | |
504 | */ | |
505 | schedule_delayed_work(&klp_transition_work, | |
506 | round_jiffies_relative(HZ)); | |
507 | return; | |
508 | } | |
509 | ||
e3ff7c60 JP |
510 | /* Done! Now cleanup the data structures. */ |
511 | klp_cond_resched_disable(); | |
958ef1e3 | 512 | patch = klp_transition_patch; |
d83a7cb3 | 513 | klp_complete_transition(); |
958ef1e3 PM |
514 | |
515 | /* | |
7e35e4eb | 516 | * It would make more sense to free the unused patches in |
958ef1e3 PM |
517 | * klp_complete_transition() but it is called also |
518 | * from klp_cancel_transition(). | |
519 | */ | |
7e35e4eb PM |
520 | if (!patch->enabled) |
521 | klp_free_patch_async(patch); | |
522 | else if (patch->replace) | |
523 | klp_free_replaced_patches_async(patch); | |
d83a7cb3 JP |
524 | } |
525 | ||
526 | /* | |
527 | * Start the transition to the specified target patch state so tasks can begin | |
528 | * switching to it. | |
529 | */ | |
530 | void klp_start_transition(void) | |
531 | { | |
532 | struct task_struct *g, *task; | |
533 | unsigned int cpu; | |
534 | ||
535 | WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); | |
536 | ||
af026796 JL |
537 | pr_notice("'%s': starting %s transition\n", |
538 | klp_transition_patch->mod->name, | |
d83a7cb3 JP |
539 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); |
540 | ||
d83a7cb3 JP |
541 | /* |
542 | * Mark all normal tasks as needing a patch state update. They'll | |
543 | * switch either in klp_try_complete_transition() or as they exit the | |
544 | * kernel. | |
545 | */ | |
546 | read_lock(&tasklist_lock); | |
547 | for_each_process_thread(g, task) | |
548 | if (task->patch_state != klp_target_state) | |
549 | set_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
550 | read_unlock(&tasklist_lock); | |
551 | ||
552 | /* | |
553 | * Mark all idle tasks as needing a patch state update. They'll switch | |
554 | * either in klp_try_complete_transition() or at the idle loop switch | |
555 | * point. | |
556 | */ | |
557 | for_each_possible_cpu(cpu) { | |
558 | task = idle_task(cpu); | |
559 | if (task->patch_state != klp_target_state) | |
560 | set_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
561 | } | |
cba82dea | 562 | |
e3ff7c60 JP |
563 | klp_cond_resched_enable(); |
564 | ||
cba82dea | 565 | klp_signals_cnt = 0; |
d83a7cb3 JP |
566 | } |
567 | ||
568 | /* | |
569 | * Initialize the global target patch state and all tasks to the initial patch | |
570 | * state, and initialize all function transition states to true in preparation | |
571 | * for patching or unpatching. | |
572 | */ | |
573 | void klp_init_transition(struct klp_patch *patch, int state) | |
574 | { | |
575 | struct task_struct *g, *task; | |
576 | unsigned int cpu; | |
577 | struct klp_object *obj; | |
578 | struct klp_func *func; | |
579 | int initial_state = !state; | |
580 | ||
581 | WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED); | |
582 | ||
583 | klp_transition_patch = patch; | |
584 | ||
585 | /* | |
586 | * Set the global target patch state which tasks will switch to. This | |
587 | * has no effect until the TIF_PATCH_PENDING flags get set later. | |
588 | */ | |
589 | klp_target_state = state; | |
590 | ||
af026796 JL |
591 | pr_debug("'%s': initializing %s transition\n", patch->mod->name, |
592 | klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); | |
593 | ||
d83a7cb3 JP |
594 | /* |
595 | * Initialize all tasks to the initial patch state to prepare them for | |
596 | * switching to the target state. | |
597 | */ | |
598 | read_lock(&tasklist_lock); | |
599 | for_each_process_thread(g, task) { | |
600 | WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); | |
601 | task->patch_state = initial_state; | |
602 | } | |
603 | read_unlock(&tasklist_lock); | |
604 | ||
605 | /* | |
606 | * Ditto for the idle "swapper" tasks. | |
607 | */ | |
608 | for_each_possible_cpu(cpu) { | |
609 | task = idle_task(cpu); | |
610 | WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); | |
611 | task->patch_state = initial_state; | |
612 | } | |
613 | ||
614 | /* | |
615 | * Enforce the order of the task->patch_state initializations and the | |
616 | * func->transition updates to ensure that klp_ftrace_handler() doesn't | |
617 | * see a func in transition with a task->patch_state of KLP_UNDEFINED. | |
618 | * | |
619 | * Also enforce the order of the klp_target_state write and future | |
e3ff7c60 JP |
620 | * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and |
621 | * __klp_sched_try_switch() don't set a task->patch_state to | |
622 | * KLP_UNDEFINED. | |
d83a7cb3 JP |
623 | */ |
624 | smp_wmb(); | |
625 | ||
626 | /* | |
627 | * Set the func transition states so klp_ftrace_handler() will know to | |
628 | * switch to the transition logic. | |
629 | * | |
630 | * When patching, the funcs aren't yet in the func_stack and will be | |
631 | * made visible to the ftrace handler shortly by the calls to | |
632 | * klp_patch_object(). | |
633 | * | |
634 | * When unpatching, the funcs are already in the func_stack and so are | |
635 | * already visible to the ftrace handler. | |
636 | */ | |
637 | klp_for_each_object(patch, obj) | |
638 | klp_for_each_func(obj, func) | |
639 | func->transition = true; | |
640 | } | |
641 | ||
642 | /* | |
643 | * This function can be called in the middle of an existing transition to | |
644 | * reverse the direction of the target patch state. This can be done to | |
645 | * effectively cancel an existing enable or disable operation if there are any | |
646 | * tasks which are stuck in the initial patch state. | |
647 | */ | |
648 | void klp_reverse_transition(void) | |
649 | { | |
650 | unsigned int cpu; | |
651 | struct task_struct *g, *task; | |
652 | ||
af026796 JL |
653 | pr_debug("'%s': reversing transition from %s\n", |
654 | klp_transition_patch->mod->name, | |
655 | klp_target_state == KLP_PATCHED ? "patching to unpatching" : | |
656 | "unpatching to patching"); | |
657 | ||
d83a7cb3 JP |
658 | /* |
659 | * Clear all TIF_PATCH_PENDING flags to prevent races caused by | |
e3ff7c60 JP |
660 | * klp_update_patch_state() or __klp_sched_try_switch() running in |
661 | * parallel with the reverse transition. | |
d83a7cb3 JP |
662 | */ |
663 | read_lock(&tasklist_lock); | |
664 | for_each_process_thread(g, task) | |
665 | clear_tsk_thread_flag(task, TIF_PATCH_PENDING); | |
666 | read_unlock(&tasklist_lock); | |
667 | ||
668 | for_each_possible_cpu(cpu) | |
669 | clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING); | |
670 | ||
e3ff7c60 JP |
671 | /* |
672 | * Make sure all existing invocations of klp_update_patch_state() and | |
673 | * __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before | |
674 | * starting the reverse transition. | |
675 | */ | |
842c0884 | 676 | klp_synchronize_transition(); |
d83a7cb3 | 677 | |
e3ff7c60 JP |
678 | /* |
679 | * All patching has stopped, now re-initialize the global variables to | |
680 | * prepare for the reverse transition. | |
681 | */ | |
682 | klp_transition_patch->enabled = !klp_transition_patch->enabled; | |
683 | klp_target_state = !klp_target_state; | |
684 | ||
685 | /* | |
686 | * Enforce the order of the klp_target_state write and the | |
687 | * TIF_PATCH_PENDING writes in klp_start_transition() to ensure | |
688 | * klp_update_patch_state() and __klp_sched_try_switch() don't set | |
689 | * task->patch_state to the wrong value. | |
690 | */ | |
691 | smp_wmb(); | |
692 | ||
d83a7cb3 JP |
693 | klp_start_transition(); |
694 | } | |
695 | ||
696 | /* Called from copy_process() during fork */ | |
697 | void klp_copy_process(struct task_struct *child) | |
698 | { | |
d83a7cb3 | 699 | |
747f7a29 RR |
700 | /* |
701 | * The parent process may have gone through a KLP transition since | |
702 | * the thread flag was copied in setup_thread_stack earlier. Bring | |
703 | * the task flag up to date with the parent here. | |
704 | * | |
705 | * The operation is serialized against all klp_*_transition() | |
e3ff7c60 JP |
706 | * operations by the tasklist_lock. The only exceptions are |
707 | * klp_update_patch_state(current) and __klp_sched_try_switch(), but we | |
708 | * cannot race with them because we are current. | |
747f7a29 RR |
709 | */ |
710 | if (test_tsk_thread_flag(current, TIF_PATCH_PENDING)) | |
711 | set_tsk_thread_flag(child, TIF_PATCH_PENDING); | |
712 | else | |
713 | clear_tsk_thread_flag(child, TIF_PATCH_PENDING); | |
714 | ||
715 | child->patch_state = current->patch_state; | |
d83a7cb3 | 716 | } |
43347d56 | 717 | |
c99a2be7 MB |
718 | /* |
719 | * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an | |
720 | * existing transition to finish. | |
721 | * | |
722 | * NOTE: klp_update_patch_state(task) requires the task to be inactive or | |
723 | * 'current'. This is not the case here and the consistency model could be | |
724 | * broken. Administrator, who is the only one to execute the | |
725 | * klp_force_transitions(), has to be aware of this. | |
726 | */ | |
727 | void klp_force_transition(void) | |
728 | { | |
68007289 | 729 | struct klp_patch *patch; |
c99a2be7 MB |
730 | struct task_struct *g, *task; |
731 | unsigned int cpu; | |
732 | ||
733 | pr_warn("forcing remaining tasks to the patched state\n"); | |
734 | ||
735 | read_lock(&tasklist_lock); | |
736 | for_each_process_thread(g, task) | |
737 | klp_update_patch_state(task); | |
738 | read_unlock(&tasklist_lock); | |
739 | ||
740 | for_each_possible_cpu(cpu) | |
741 | klp_update_patch_state(idle_task(cpu)); | |
742 | ||
29573083 CZ |
743 | /* Set forced flag for patches being removed. */ |
744 | if (klp_target_state == KLP_UNPATCHED) | |
745 | klp_transition_patch->forced = true; | |
746 | else if (klp_transition_patch->replace) { | |
747 | klp_for_each_patch(patch) { | |
748 | if (patch != klp_transition_patch) | |
749 | patch->forced = true; | |
750 | } | |
751 | } | |
c99a2be7 | 752 | } |