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Thomas Gleixner1ccea772019-05-19 15:51:43 +02001// SPDX-License-Identifier: GPL-2.0-or-later
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -06002/*
3 * transition.c - Kernel Live Patching transition functions
4 *
5 * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com>
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -06006 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/cpu.h>
11#include <linux/stacktrace.h>
Jiri Kosina10517422017-03-08 14:27:05 +010012#include "core.h"
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -060013#include "patch.h"
14#include "transition.h"
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -060015
16#define MAX_STACK_ENTRIES 100
17#define STACK_ERR_BUF_SIZE 128
18
Miroslav Benescba82de2019-01-15 17:45:06 +010019#define SIGNALS_TIMEOUT 15
20
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -060021struct klp_patch *klp_transition_patch;
22
23static int klp_target_state = KLP_UNDEFINED;
24
Miroslav Benescba82de2019-01-15 17:45:06 +010025static unsigned int klp_signals_cnt;
26
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -060027/*
28 * This work can be performed periodically to finish patching or unpatching any
29 * "straggler" tasks which failed to transition in the first attempt.
30 */
31static void klp_transition_work_fn(struct work_struct *work)
32{
33 mutex_lock(&klp_mutex);
34
35 if (klp_transition_patch)
36 klp_try_complete_transition();
37
38 mutex_unlock(&klp_mutex);
39}
40static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
41
42/*
Petr Mladek842c0882017-06-14 10:54:52 +020043 * This function is just a stub to implement a hard force
Paul E. McKenney69326892018-11-07 14:16:57 -080044 * of synchronize_rcu(). This requires synchronizing
Petr Mladek842c0882017-06-14 10:54:52 +020045 * tasks even in userspace and idle.
46 */
47static void klp_sync(struct work_struct *work)
48{
49}
50
51/*
52 * We allow to patch also functions where RCU is not watching,
53 * e.g. before user_exit(). We can not rely on the RCU infrastructure
54 * to do the synchronization. Instead hard force the sched synchronization.
55 *
56 * This approach allows to use RCU functions for manipulating func_stack
57 * safely.
58 */
59static void klp_synchronize_transition(void)
60{
61 schedule_on_each_cpu(klp_sync);
62}
63
64/*
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -060065 * The transition to the target patch state is complete. Clean up the data
66 * structures.
67 */
68static void klp_complete_transition(void)
69{
70 struct klp_object *obj;
71 struct klp_func *func;
72 struct task_struct *g, *task;
73 unsigned int cpu;
74
Joe Lawrenceaf026792017-10-13 15:08:43 -040075 pr_debug("'%s': completing %s transition\n",
76 klp_transition_patch->mod->name,
77 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
78
Petr Mladekd697bad2019-01-09 13:43:26 +010079 if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) {
Petr Mladek7e35e4e2019-10-30 16:43:09 +010080 klp_unpatch_replaced_patches(klp_transition_patch);
Petr Mladekd697bad2019-01-09 13:43:26 +010081 klp_discard_nops(klp_transition_patch);
82 }
Jason Barone1452b62019-01-09 13:43:25 +010083
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -060084 if (klp_target_state == KLP_UNPATCHED) {
85 /*
86 * All tasks have transitioned to KLP_UNPATCHED so we can now
87 * remove the new functions from the func_stack.
88 */
89 klp_unpatch_objects(klp_transition_patch);
90
91 /*
92 * Make sure klp_ftrace_handler() can no longer see functions
93 * from this patch on the ops->func_stack. Otherwise, after
94 * func->transition gets cleared, the handler may choose a
95 * removed function.
96 */
Petr Mladek842c0882017-06-14 10:54:52 +020097 klp_synchronize_transition();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -060098 }
99
Miroslav Benesd0807da2018-01-10 11:01:28 +0100100 klp_for_each_object(klp_transition_patch, obj)
101 klp_for_each_func(obj, func)
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600102 func->transition = false;
Josh Poimboeuf3ec24772017-03-06 11:20:29 -0600103
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600104 /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
105 if (klp_target_state == KLP_PATCHED)
Petr Mladek842c0882017-06-14 10:54:52 +0200106 klp_synchronize_transition();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600107
108 read_lock(&tasklist_lock);
109 for_each_process_thread(g, task) {
110 WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
111 task->patch_state = KLP_UNDEFINED;
112 }
113 read_unlock(&tasklist_lock);
114
115 for_each_possible_cpu(cpu) {
116 task = idle_task(cpu);
117 WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
118 task->patch_state = KLP_UNDEFINED;
119 }
120
Joe Lawrence93862e32017-10-13 15:08:41 -0400121 klp_for_each_object(klp_transition_patch, obj) {
122 if (!klp_is_object_loaded(obj))
123 continue;
124 if (klp_target_state == KLP_PATCHED)
125 klp_post_patch_callback(obj);
126 else if (klp_target_state == KLP_UNPATCHED)
127 klp_post_unpatch_callback(obj);
128 }
129
Joe Lawrence6116c302017-10-13 15:08:42 -0400130 pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
131 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
132
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600133 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 */
143void klp_cancel_transition(void)
144{
Josh Poimboeuf3ec24772017-03-06 11:20:29 -0600145 if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
146 return;
147
Joe Lawrenceaf026792017-10-13 15:08:43 -0400148 pr_debug("'%s': canceling patching transition, going to unpatch\n",
149 klp_transition_patch->mod->name);
150
Josh Poimboeuf3ec24772017-03-06 11:20:29 -0600151 klp_target_state = KLP_UNPATCHED;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600152 klp_complete_transition();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600153}
154
155/*
156 * Switch the patched state of the task to the set of functions in the target
157 * patch state.
158 *
159 * NOTE: If task is not 'current', the caller must ensure the task is inactive.
160 * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value.
161 */
162void klp_update_patch_state(struct task_struct *task)
163{
Petr Mladek842c0882017-06-14 10:54:52 +0200164 /*
Paul E. McKenney69326892018-11-07 14:16:57 -0800165 * A variant of synchronize_rcu() is used to allow patching functions
Petr Mladek842c0882017-06-14 10:54:52 +0200166 * where RCU is not watching, see klp_synchronize_transition().
167 */
168 preempt_disable_notrace();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600169
170 /*
171 * This test_and_clear_tsk_thread_flag() call also serves as a read
172 * barrier (smp_rmb) for two cases:
173 *
174 * 1) Enforce the order of the TIF_PATCH_PENDING read and the
175 * klp_target_state read. The corresponding write barrier is in
176 * klp_init_transition().
177 *
178 * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
179 * of func->transition, if klp_ftrace_handler() is called later on
180 * the same CPU. See __klp_disable_patch().
181 */
182 if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
183 task->patch_state = READ_ONCE(klp_target_state);
184
Petr Mladek842c0882017-06-14 10:54:52 +0200185 preempt_enable_notrace();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600186}
187
188/*
189 * Determine whether the given stack trace includes any references to a
190 * to-be-patched or to-be-unpatched function.
191 */
Thomas Gleixner25e39e32019-04-25 11:45:18 +0200192static int klp_check_stack_func(struct klp_func *func, unsigned long *entries,
193 unsigned int nr_entries)
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600194{
195 unsigned long func_addr, func_size, address;
196 struct klp_ops *ops;
197 int i;
198
Thomas Gleixner25e39e32019-04-25 11:45:18 +0200199 for (i = 0; i < nr_entries; i++) {
200 address = entries[i];
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600201
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 */
Petr Mladek19514912019-01-09 13:43:19 +0100214 ops = klp_find_ops(func->old_func);
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600215
216 if (list_is_singular(&ops->func_stack)) {
217 /* original function */
Petr Mladek19514912019-01-09 13:43:19 +0100218 func_addr = (unsigned long)func->old_func;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600219 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 */
Peter Zijlstra00619f72021-09-21 21:54:32 +0200241static int klp_check_stack(struct task_struct *task, const char **oldname)
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600242{
243 static unsigned long entries[MAX_STACK_ENTRIES];
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600244 struct klp_object *obj;
245 struct klp_func *func;
Thomas Gleixner25e39e32019-04-25 11:45:18 +0200246 int ret, nr_entries;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600247
Thomas Gleixner25e39e32019-04-25 11:45:18 +0200248 ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries));
Peter Zijlstra00619f72021-09-21 21:54:32 +0200249 if (ret < 0)
250 return -EINVAL;
Thomas Gleixner25e39e32019-04-25 11:45:18 +0200251 nr_entries = ret;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600252
253 klp_for_each_object(klp_transition_patch, obj) {
254 if (!obj->patched)
255 continue;
256 klp_for_each_func(obj, func) {
Thomas Gleixner25e39e32019-04-25 11:45:18 +0200257 ret = klp_check_stack_func(func, entries, nr_entries);
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600258 if (ret) {
Peter Zijlstra00619f72021-09-21 21:54:32 +0200259 *oldname = func->old_name;
260 return -EADDRINUSE;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600261 }
262 }
263 }
264
265 return 0;
266}
267
Peter Zijlstra00619f72021-09-21 21:54:32 +0200268static int klp_check_and_switch_task(struct task_struct *task, void *arg)
269{
270 int ret;
271
272 if (task_curr(task) && task != current)
273 return -EBUSY;
274
275 ret = klp_check_stack(task, arg);
276 if (ret)
277 return ret;
278
279 clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
280 task->patch_state = klp_target_state;
281 return 0;
282}
283
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600284/*
285 * Try to safely switch a task to the target patch state. If it's currently
286 * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
287 * if the stack is unreliable, return false.
288 */
289static bool klp_try_switch_task(struct task_struct *task)
290{
Peter Zijlstra00619f72021-09-21 21:54:32 +0200291 const char *old_name;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600292 int ret;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600293
294 /* check if this task has already switched over */
295 if (task->patch_state == klp_target_state)
296 return true;
297
298 /*
Miroslav Benes67059d62019-06-11 16:13:19 +0200299 * For arches which don't have reliable stack traces, we have to rely
300 * on other methods (e.g., switching tasks at kernel exit).
301 */
302 if (!klp_have_reliable_stack())
303 return false;
304
305 /*
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600306 * Now try to check the stack for any to-be-patched or to-be-unpatched
307 * functions. If all goes well, switch the task to the target patch
308 * state.
309 */
Peter Zijlstra00619f72021-09-21 21:54:32 +0200310 ret = task_call_func(task, klp_check_and_switch_task, &old_name);
311 switch (ret) {
312 case 0: /* success */
313 break;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600314
Peter Zijlstra00619f72021-09-21 21:54:32 +0200315 case -EBUSY: /* klp_check_and_switch_task() */
316 pr_debug("%s: %s:%d is running\n",
317 __func__, task->comm, task->pid);
318 break;
319 case -EINVAL: /* klp_check_and_switch_task() */
320 pr_debug("%s: %s:%d has an unreliable stack\n",
321 __func__, task->comm, task->pid);
322 break;
323 case -EADDRINUSE: /* klp_check_and_switch_task() */
324 pr_debug("%s: %s:%d is sleeping on function %s\n",
325 __func__, task->comm, task->pid, old_name);
326 break;
327
328 default:
329 pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n",
330 __func__, ret, task->comm, task->pid);
331 break;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600332 }
333
Peter Zijlstra00619f72021-09-21 21:54:32 +0200334 return !ret;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600335}
336
337/*
Miroslav Benes0b3d5272019-01-15 17:45:07 +0100338 * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
339 * Kthreads with TIF_PATCH_PENDING set are woken up.
340 */
341static void klp_send_signals(void)
342{
343 struct task_struct *g, *task;
344
345 if (klp_signals_cnt == SIGNALS_TIMEOUT)
346 pr_notice("signaling remaining tasks\n");
347
348 read_lock(&tasklist_lock);
349 for_each_process_thread(g, task) {
350 if (!klp_patch_pending(task))
351 continue;
352
353 /*
354 * There is a small race here. We could see TIF_PATCH_PENDING
355 * set and decide to wake up a kthread or send a fake signal.
356 * Meanwhile the task could migrate itself and the action
357 * would be meaningless. It is not serious though.
358 */
359 if (task->flags & PF_KTHREAD) {
360 /*
361 * Wake up a kthread which sleeps interruptedly and
362 * still has not been migrated.
363 */
364 wake_up_state(task, TASK_INTERRUPTIBLE);
365 } else {
366 /*
367 * Send fake signal to all non-kthread tasks which are
368 * still not migrated.
369 */
Miroslav Benes8df19472021-03-29 15:28:15 +0200370 set_notify_signal(task);
Miroslav Benes0b3d5272019-01-15 17:45:07 +0100371 }
372 }
373 read_unlock(&tasklist_lock);
374}
375
376/*
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600377 * Try to switch all remaining tasks to the target patch state by walking the
378 * stacks of sleeping tasks and looking for any to-be-patched or
379 * to-be-unpatched functions. If such functions are found, the task can't be
380 * switched yet.
381 *
382 * If any tasks are still stuck in the initial patch state, schedule a retry.
383 */
384void klp_try_complete_transition(void)
385{
386 unsigned int cpu;
387 struct task_struct *g, *task;
Petr Mladek958ef1e2019-01-09 13:43:23 +0100388 struct klp_patch *patch;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600389 bool complete = true;
390
391 WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
392
393 /*
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600394 * Try to switch the tasks to the target patch state by walking their
395 * stacks and looking for any to-be-patched or to-be-unpatched
396 * functions. If such functions are found on a stack, or if the stack
397 * is deemed unreliable, the task can't be switched yet.
398 *
399 * Usually this will transition most (or all) of the tasks on a system
400 * unless the patch includes changes to a very common function.
401 */
402 read_lock(&tasklist_lock);
403 for_each_process_thread(g, task)
404 if (!klp_try_switch_task(task))
405 complete = false;
406 read_unlock(&tasklist_lock);
407
408 /*
409 * Ditto for the idle "swapper" tasks.
410 */
Sebastian Andrzej Siewior1daf08a2021-08-03 16:16:09 +0200411 cpus_read_lock();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600412 for_each_possible_cpu(cpu) {
413 task = idle_task(cpu);
414 if (cpu_online(cpu)) {
Peter Zijlstra5de62ea2021-09-21 22:16:02 +0200415 if (!klp_try_switch_task(task)) {
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600416 complete = false;
Peter Zijlstra5de62ea2021-09-21 22:16:02 +0200417 /* Make idle task go through the main loop. */
418 wake_up_if_idle(cpu);
419 }
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600420 } else if (task->patch_state != klp_target_state) {
421 /* offline idle tasks can be switched immediately */
422 clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
423 task->patch_state = klp_target_state;
424 }
425 }
Sebastian Andrzej Siewior1daf08a2021-08-03 16:16:09 +0200426 cpus_read_unlock();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600427
428 if (!complete) {
Miroslav Benescba82de2019-01-15 17:45:06 +0100429 if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT))
430 klp_send_signals();
431 klp_signals_cnt++;
432
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600433 /*
434 * Some tasks weren't able to be switched over. Try again
435 * later and/or wait for other methods like kernel exit
436 * switching.
437 */
438 schedule_delayed_work(&klp_transition_work,
439 round_jiffies_relative(HZ));
440 return;
441 }
442
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600443 /* we're done, now cleanup the data structures */
Petr Mladek958ef1e2019-01-09 13:43:23 +0100444 patch = klp_transition_patch;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600445 klp_complete_transition();
Petr Mladek958ef1e2019-01-09 13:43:23 +0100446
447 /*
Petr Mladek7e35e4e2019-10-30 16:43:09 +0100448 * It would make more sense to free the unused patches in
Petr Mladek958ef1e2019-01-09 13:43:23 +0100449 * klp_complete_transition() but it is called also
450 * from klp_cancel_transition().
451 */
Petr Mladek7e35e4e2019-10-30 16:43:09 +0100452 if (!patch->enabled)
453 klp_free_patch_async(patch);
454 else if (patch->replace)
455 klp_free_replaced_patches_async(patch);
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600456}
457
458/*
459 * Start the transition to the specified target patch state so tasks can begin
460 * switching to it.
461 */
462void klp_start_transition(void)
463{
464 struct task_struct *g, *task;
465 unsigned int cpu;
466
467 WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
468
Joe Lawrenceaf026792017-10-13 15:08:43 -0400469 pr_notice("'%s': starting %s transition\n",
470 klp_transition_patch->mod->name,
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600471 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
472
473 /*
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600474 * Mark all normal tasks as needing a patch state update. They'll
475 * switch either in klp_try_complete_transition() or as they exit the
476 * kernel.
477 */
478 read_lock(&tasklist_lock);
479 for_each_process_thread(g, task)
480 if (task->patch_state != klp_target_state)
481 set_tsk_thread_flag(task, TIF_PATCH_PENDING);
482 read_unlock(&tasklist_lock);
483
484 /*
485 * Mark all idle tasks as needing a patch state update. They'll switch
486 * either in klp_try_complete_transition() or at the idle loop switch
487 * point.
488 */
489 for_each_possible_cpu(cpu) {
490 task = idle_task(cpu);
491 if (task->patch_state != klp_target_state)
492 set_tsk_thread_flag(task, TIF_PATCH_PENDING);
493 }
Miroslav Benescba82de2019-01-15 17:45:06 +0100494
495 klp_signals_cnt = 0;
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600496}
497
498/*
499 * Initialize the global target patch state and all tasks to the initial patch
500 * state, and initialize all function transition states to true in preparation
501 * for patching or unpatching.
502 */
503void klp_init_transition(struct klp_patch *patch, int state)
504{
505 struct task_struct *g, *task;
506 unsigned int cpu;
507 struct klp_object *obj;
508 struct klp_func *func;
509 int initial_state = !state;
510
511 WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED);
512
513 klp_transition_patch = patch;
514
515 /*
516 * Set the global target patch state which tasks will switch to. This
517 * has no effect until the TIF_PATCH_PENDING flags get set later.
518 */
519 klp_target_state = state;
520
Joe Lawrenceaf026792017-10-13 15:08:43 -0400521 pr_debug("'%s': initializing %s transition\n", patch->mod->name,
522 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
523
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600524 /*
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600525 * Initialize all tasks to the initial patch state to prepare them for
526 * switching to the target state.
527 */
528 read_lock(&tasklist_lock);
529 for_each_process_thread(g, task) {
530 WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
531 task->patch_state = initial_state;
532 }
533 read_unlock(&tasklist_lock);
534
535 /*
536 * Ditto for the idle "swapper" tasks.
537 */
538 for_each_possible_cpu(cpu) {
539 task = idle_task(cpu);
540 WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
541 task->patch_state = initial_state;
542 }
543
544 /*
545 * Enforce the order of the task->patch_state initializations and the
546 * func->transition updates to ensure that klp_ftrace_handler() doesn't
547 * see a func in transition with a task->patch_state of KLP_UNDEFINED.
548 *
549 * Also enforce the order of the klp_target_state write and future
550 * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
551 * set a task->patch_state to KLP_UNDEFINED.
552 */
553 smp_wmb();
554
555 /*
556 * Set the func transition states so klp_ftrace_handler() will know to
557 * switch to the transition logic.
558 *
559 * When patching, the funcs aren't yet in the func_stack and will be
560 * made visible to the ftrace handler shortly by the calls to
561 * klp_patch_object().
562 *
563 * When unpatching, the funcs are already in the func_stack and so are
564 * already visible to the ftrace handler.
565 */
566 klp_for_each_object(patch, obj)
567 klp_for_each_func(obj, func)
568 func->transition = true;
569}
570
571/*
572 * This function can be called in the middle of an existing transition to
573 * reverse the direction of the target patch state. This can be done to
574 * effectively cancel an existing enable or disable operation if there are any
575 * tasks which are stuck in the initial patch state.
576 */
577void klp_reverse_transition(void)
578{
579 unsigned int cpu;
580 struct task_struct *g, *task;
581
Joe Lawrenceaf026792017-10-13 15:08:43 -0400582 pr_debug("'%s': reversing transition from %s\n",
583 klp_transition_patch->mod->name,
584 klp_target_state == KLP_PATCHED ? "patching to unpatching" :
585 "unpatching to patching");
586
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600587 klp_transition_patch->enabled = !klp_transition_patch->enabled;
588
589 klp_target_state = !klp_target_state;
590
591 /*
592 * Clear all TIF_PATCH_PENDING flags to prevent races caused by
593 * klp_update_patch_state() running in parallel with
594 * klp_start_transition().
595 */
596 read_lock(&tasklist_lock);
597 for_each_process_thread(g, task)
598 clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
599 read_unlock(&tasklist_lock);
600
601 for_each_possible_cpu(cpu)
602 clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
603
604 /* Let any remaining calls to klp_update_patch_state() complete */
Petr Mladek842c0882017-06-14 10:54:52 +0200605 klp_synchronize_transition();
Josh Poimboeufd83a7cb2017-02-13 19:42:40 -0600606
607 klp_start_transition();
608}
609
610/* Called from copy_process() during fork */
611void klp_copy_process(struct task_struct *child)
612{
613 child->patch_state = current->patch_state;
614
615 /* TIF_PATCH_PENDING gets copied in setup_thread_stack() */
616}
Miroslav Benes43347d52017-11-15 14:50:13 +0100617
618/*
Miroslav Benesc99a2be2017-11-22 11:29:21 +0100619 * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an
620 * existing transition to finish.
621 *
622 * NOTE: klp_update_patch_state(task) requires the task to be inactive or
623 * 'current'. This is not the case here and the consistency model could be
624 * broken. Administrator, who is the only one to execute the
625 * klp_force_transitions(), has to be aware of this.
626 */
627void klp_force_transition(void)
628{
Petr Mladek68007282019-01-09 13:43:22 +0100629 struct klp_patch *patch;
Miroslav Benesc99a2be2017-11-22 11:29:21 +0100630 struct task_struct *g, *task;
631 unsigned int cpu;
632
633 pr_warn("forcing remaining tasks to the patched state\n");
634
635 read_lock(&tasklist_lock);
636 for_each_process_thread(g, task)
637 klp_update_patch_state(task);
638 read_unlock(&tasklist_lock);
639
640 for_each_possible_cpu(cpu)
641 klp_update_patch_state(idle_task(cpu));
642
Chengming Zhou29573082022-03-12 23:22:20 +0800643 /* Set forced flag for patches being removed. */
644 if (klp_target_state == KLP_UNPATCHED)
645 klp_transition_patch->forced = true;
646 else if (klp_transition_patch->replace) {
647 klp_for_each_patch(patch) {
648 if (patch != klp_transition_patch)
649 patch->forced = true;
650 }
651 }
Miroslav Benesc99a2be2017-11-22 11:29:21 +0100652}