| // SPDX-License-Identifier: GPL-2.0-or-later |
| /* |
| * transition.c - Kernel Live Patching transition functions |
| * |
| * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com> |
| */ |
| |
| #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
| |
| #include <linux/cpu.h> |
| #include <linux/stacktrace.h> |
| #include "core.h" |
| #include "patch.h" |
| #include "transition.h" |
| |
| #define MAX_STACK_ENTRIES 100 |
| #define STACK_ERR_BUF_SIZE 128 |
| |
| #define SIGNALS_TIMEOUT 15 |
| |
| struct klp_patch *klp_transition_patch; |
| |
| static int klp_target_state = KLP_UNDEFINED; |
| |
| static unsigned int klp_signals_cnt; |
| |
| /* |
| * This work can be performed periodically to finish patching or unpatching any |
| * "straggler" tasks which failed to transition in the first attempt. |
| */ |
| static void klp_transition_work_fn(struct work_struct *work) |
| { |
| mutex_lock(&klp_mutex); |
| |
| if (klp_transition_patch) |
| klp_try_complete_transition(); |
| |
| mutex_unlock(&klp_mutex); |
| } |
| static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn); |
| |
| /* |
| * This function is just a stub to implement a hard force |
| * of synchronize_rcu(). This requires synchronizing |
| * tasks even in userspace and idle. |
| */ |
| static void klp_sync(struct work_struct *work) |
| { |
| } |
| |
| /* |
| * We allow to patch also functions where RCU is not watching, |
| * e.g. before user_exit(). We can not rely on the RCU infrastructure |
| * to do the synchronization. Instead hard force the sched synchronization. |
| * |
| * This approach allows to use RCU functions for manipulating func_stack |
| * safely. |
| */ |
| static void klp_synchronize_transition(void) |
| { |
| schedule_on_each_cpu(klp_sync); |
| } |
| |
| /* |
| * The transition to the target patch state is complete. Clean up the data |
| * structures. |
| */ |
| static void klp_complete_transition(void) |
| { |
| struct klp_object *obj; |
| struct klp_func *func; |
| struct task_struct *g, *task; |
| unsigned int cpu; |
| |
| pr_debug("'%s': completing %s transition\n", |
| klp_transition_patch->mod->name, |
| klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); |
| |
| if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) { |
| klp_unpatch_replaced_patches(klp_transition_patch); |
| klp_discard_nops(klp_transition_patch); |
| } |
| |
| if (klp_target_state == KLP_UNPATCHED) { |
| /* |
| * All tasks have transitioned to KLP_UNPATCHED so we can now |
| * remove the new functions from the func_stack. |
| */ |
| klp_unpatch_objects(klp_transition_patch); |
| |
| /* |
| * Make sure klp_ftrace_handler() can no longer see functions |
| * from this patch on the ops->func_stack. Otherwise, after |
| * func->transition gets cleared, the handler may choose a |
| * removed function. |
| */ |
| klp_synchronize_transition(); |
| } |
| |
| klp_for_each_object(klp_transition_patch, obj) |
| klp_for_each_func(obj, func) |
| func->transition = false; |
| |
| /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ |
| if (klp_target_state == KLP_PATCHED) |
| klp_synchronize_transition(); |
| |
| read_lock(&tasklist_lock); |
| for_each_process_thread(g, task) { |
| WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); |
| task->patch_state = KLP_UNDEFINED; |
| } |
| read_unlock(&tasklist_lock); |
| |
| for_each_possible_cpu(cpu) { |
| task = idle_task(cpu); |
| WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); |
| task->patch_state = KLP_UNDEFINED; |
| } |
| |
| klp_for_each_object(klp_transition_patch, obj) { |
| if (!klp_is_object_loaded(obj)) |
| continue; |
| if (klp_target_state == KLP_PATCHED) |
| klp_post_patch_callback(obj); |
| else if (klp_target_state == KLP_UNPATCHED) |
| klp_post_unpatch_callback(obj); |
| } |
| |
| pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name, |
| klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); |
| |
| klp_target_state = KLP_UNDEFINED; |
| klp_transition_patch = NULL; |
| } |
| |
| /* |
| * This is called in the error path, to cancel a transition before it has |
| * started, i.e. klp_init_transition() has been called but |
| * klp_start_transition() hasn't. If the transition *has* been started, |
| * klp_reverse_transition() should be used instead. |
| */ |
| void klp_cancel_transition(void) |
| { |
| if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED)) |
| return; |
| |
| pr_debug("'%s': canceling patching transition, going to unpatch\n", |
| klp_transition_patch->mod->name); |
| |
| klp_target_state = KLP_UNPATCHED; |
| klp_complete_transition(); |
| } |
| |
| /* |
| * Switch the patched state of the task to the set of functions in the target |
| * patch state. |
| * |
| * NOTE: If task is not 'current', the caller must ensure the task is inactive. |
| * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value. |
| */ |
| void klp_update_patch_state(struct task_struct *task) |
| { |
| /* |
| * A variant of synchronize_rcu() is used to allow patching functions |
| * where RCU is not watching, see klp_synchronize_transition(). |
| */ |
| preempt_disable_notrace(); |
| |
| /* |
| * This test_and_clear_tsk_thread_flag() call also serves as a read |
| * barrier (smp_rmb) for two cases: |
| * |
| * 1) Enforce the order of the TIF_PATCH_PENDING read and the |
| * klp_target_state read. The corresponding write barrier is in |
| * klp_init_transition(). |
| * |
| * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read |
| * of func->transition, if klp_ftrace_handler() is called later on |
| * the same CPU. See __klp_disable_patch(). |
| */ |
| if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING)) |
| task->patch_state = READ_ONCE(klp_target_state); |
| |
| preempt_enable_notrace(); |
| } |
| |
| /* |
| * Determine whether the given stack trace includes any references to a |
| * to-be-patched or to-be-unpatched function. |
| */ |
| static int klp_check_stack_func(struct klp_func *func, unsigned long *entries, |
| unsigned int nr_entries) |
| { |
| unsigned long func_addr, func_size, address; |
| struct klp_ops *ops; |
| int i; |
| |
| for (i = 0; i < nr_entries; i++) { |
| address = entries[i]; |
| |
| if (klp_target_state == KLP_UNPATCHED) { |
| /* |
| * Check for the to-be-unpatched function |
| * (the func itself). |
| */ |
| func_addr = (unsigned long)func->new_func; |
| func_size = func->new_size; |
| } else { |
| /* |
| * Check for the to-be-patched function |
| * (the previous func). |
| */ |
| ops = klp_find_ops(func->old_func); |
| |
| if (list_is_singular(&ops->func_stack)) { |
| /* original function */ |
| func_addr = (unsigned long)func->old_func; |
| func_size = func->old_size; |
| } else { |
| /* previously patched function */ |
| struct klp_func *prev; |
| |
| prev = list_next_entry(func, stack_node); |
| func_addr = (unsigned long)prev->new_func; |
| func_size = prev->new_size; |
| } |
| } |
| |
| if (address >= func_addr && address < func_addr + func_size) |
| return -EAGAIN; |
| } |
| |
| return 0; |
| } |
| |
| /* |
| * Determine whether it's safe to transition the task to the target patch state |
| * by looking for any to-be-patched or to-be-unpatched functions on its stack. |
| */ |
| static int klp_check_stack(struct task_struct *task, const char **oldname) |
| { |
| static unsigned long entries[MAX_STACK_ENTRIES]; |
| struct klp_object *obj; |
| struct klp_func *func; |
| int ret, nr_entries; |
| |
| ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries)); |
| if (ret < 0) |
| return -EINVAL; |
| nr_entries = ret; |
| |
| klp_for_each_object(klp_transition_patch, obj) { |
| if (!obj->patched) |
| continue; |
| klp_for_each_func(obj, func) { |
| ret = klp_check_stack_func(func, entries, nr_entries); |
| if (ret) { |
| *oldname = func->old_name; |
| return -EADDRINUSE; |
| } |
| } |
| } |
| |
| return 0; |
| } |
| |
| static int klp_check_and_switch_task(struct task_struct *task, void *arg) |
| { |
| int ret; |
| |
| if (task_curr(task) && task != current) |
| return -EBUSY; |
| |
| ret = klp_check_stack(task, arg); |
| if (ret) |
| return ret; |
| |
| clear_tsk_thread_flag(task, TIF_PATCH_PENDING); |
| task->patch_state = klp_target_state; |
| return 0; |
| } |
| |
| /* |
| * Try to safely switch a task to the target patch state. If it's currently |
| * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or |
| * if the stack is unreliable, return false. |
| */ |
| static bool klp_try_switch_task(struct task_struct *task) |
| { |
| const char *old_name; |
| int ret; |
| |
| /* check if this task has already switched over */ |
| if (task->patch_state == klp_target_state) |
| return true; |
| |
| /* |
| * For arches which don't have reliable stack traces, we have to rely |
| * on other methods (e.g., switching tasks at kernel exit). |
| */ |
| if (!klp_have_reliable_stack()) |
| return false; |
| |
| /* |
| * Now try to check the stack for any to-be-patched or to-be-unpatched |
| * functions. If all goes well, switch the task to the target patch |
| * state. |
| */ |
| ret = task_call_func(task, klp_check_and_switch_task, &old_name); |
| switch (ret) { |
| case 0: /* success */ |
| break; |
| |
| case -EBUSY: /* klp_check_and_switch_task() */ |
| pr_debug("%s: %s:%d is running\n", |
| __func__, task->comm, task->pid); |
| break; |
| case -EINVAL: /* klp_check_and_switch_task() */ |
| pr_debug("%s: %s:%d has an unreliable stack\n", |
| __func__, task->comm, task->pid); |
| break; |
| case -EADDRINUSE: /* klp_check_and_switch_task() */ |
| pr_debug("%s: %s:%d is sleeping on function %s\n", |
| __func__, task->comm, task->pid, old_name); |
| break; |
| |
| default: |
| pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n", |
| __func__, ret, task->comm, task->pid); |
| break; |
| } |
| |
| return !ret; |
| } |
| |
| /* |
| * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. |
| * Kthreads with TIF_PATCH_PENDING set are woken up. |
| */ |
| static void klp_send_signals(void) |
| { |
| struct task_struct *g, *task; |
| |
| if (klp_signals_cnt == SIGNALS_TIMEOUT) |
| pr_notice("signaling remaining tasks\n"); |
| |
| read_lock(&tasklist_lock); |
| for_each_process_thread(g, task) { |
| if (!klp_patch_pending(task)) |
| continue; |
| |
| /* |
| * There is a small race here. We could see TIF_PATCH_PENDING |
| * set and decide to wake up a kthread or send a fake signal. |
| * Meanwhile the task could migrate itself and the action |
| * would be meaningless. It is not serious though. |
| */ |
| if (task->flags & PF_KTHREAD) { |
| /* |
| * Wake up a kthread which sleeps interruptedly and |
| * still has not been migrated. |
| */ |
| wake_up_state(task, TASK_INTERRUPTIBLE); |
| } else { |
| /* |
| * Send fake signal to all non-kthread tasks which are |
| * still not migrated. |
| */ |
| set_notify_signal(task); |
| } |
| } |
| read_unlock(&tasklist_lock); |
| } |
| |
| /* |
| * Try to switch all remaining tasks to the target patch state by walking the |
| * stacks of sleeping tasks and looking for any to-be-patched or |
| * to-be-unpatched functions. If such functions are found, the task can't be |
| * switched yet. |
| * |
| * If any tasks are still stuck in the initial patch state, schedule a retry. |
| */ |
| void klp_try_complete_transition(void) |
| { |
| unsigned int cpu; |
| struct task_struct *g, *task; |
| struct klp_patch *patch; |
| bool complete = true; |
| |
| WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); |
| |
| /* |
| * Try to switch the tasks to the target patch state by walking their |
| * stacks and looking for any to-be-patched or to-be-unpatched |
| * functions. If such functions are found on a stack, or if the stack |
| * is deemed unreliable, the task can't be switched yet. |
| * |
| * Usually this will transition most (or all) of the tasks on a system |
| * unless the patch includes changes to a very common function. |
| */ |
| read_lock(&tasklist_lock); |
| for_each_process_thread(g, task) |
| if (!klp_try_switch_task(task)) |
| complete = false; |
| read_unlock(&tasklist_lock); |
| |
| /* |
| * Ditto for the idle "swapper" tasks. |
| */ |
| cpus_read_lock(); |
| for_each_possible_cpu(cpu) { |
| task = idle_task(cpu); |
| if (cpu_online(cpu)) { |
| if (!klp_try_switch_task(task)) { |
| complete = false; |
| /* Make idle task go through the main loop. */ |
| wake_up_if_idle(cpu); |
| } |
| } else if (task->patch_state != klp_target_state) { |
| /* offline idle tasks can be switched immediately */ |
| clear_tsk_thread_flag(task, TIF_PATCH_PENDING); |
| task->patch_state = klp_target_state; |
| } |
| } |
| cpus_read_unlock(); |
| |
| if (!complete) { |
| if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT)) |
| klp_send_signals(); |
| klp_signals_cnt++; |
| |
| /* |
| * Some tasks weren't able to be switched over. Try again |
| * later and/or wait for other methods like kernel exit |
| * switching. |
| */ |
| schedule_delayed_work(&klp_transition_work, |
| round_jiffies_relative(HZ)); |
| return; |
| } |
| |
| /* we're done, now cleanup the data structures */ |
| patch = klp_transition_patch; |
| klp_complete_transition(); |
| |
| /* |
| * It would make more sense to free the unused patches in |
| * klp_complete_transition() but it is called also |
| * from klp_cancel_transition(). |
| */ |
| if (!patch->enabled) |
| klp_free_patch_async(patch); |
| else if (patch->replace) |
| klp_free_replaced_patches_async(patch); |
| } |
| |
| /* |
| * Start the transition to the specified target patch state so tasks can begin |
| * switching to it. |
| */ |
| void klp_start_transition(void) |
| { |
| struct task_struct *g, *task; |
| unsigned int cpu; |
| |
| WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); |
| |
| pr_notice("'%s': starting %s transition\n", |
| klp_transition_patch->mod->name, |
| klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); |
| |
| /* |
| * Mark all normal tasks as needing a patch state update. They'll |
| * switch either in klp_try_complete_transition() or as they exit the |
| * kernel. |
| */ |
| read_lock(&tasklist_lock); |
| for_each_process_thread(g, task) |
| if (task->patch_state != klp_target_state) |
| set_tsk_thread_flag(task, TIF_PATCH_PENDING); |
| read_unlock(&tasklist_lock); |
| |
| /* |
| * Mark all idle tasks as needing a patch state update. They'll switch |
| * either in klp_try_complete_transition() or at the idle loop switch |
| * point. |
| */ |
| for_each_possible_cpu(cpu) { |
| task = idle_task(cpu); |
| if (task->patch_state != klp_target_state) |
| set_tsk_thread_flag(task, TIF_PATCH_PENDING); |
| } |
| |
| klp_signals_cnt = 0; |
| } |
| |
| /* |
| * Initialize the global target patch state and all tasks to the initial patch |
| * state, and initialize all function transition states to true in preparation |
| * for patching or unpatching. |
| */ |
| void klp_init_transition(struct klp_patch *patch, int state) |
| { |
| struct task_struct *g, *task; |
| unsigned int cpu; |
| struct klp_object *obj; |
| struct klp_func *func; |
| int initial_state = !state; |
| |
| WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED); |
| |
| klp_transition_patch = patch; |
| |
| /* |
| * Set the global target patch state which tasks will switch to. This |
| * has no effect until the TIF_PATCH_PENDING flags get set later. |
| */ |
| klp_target_state = state; |
| |
| pr_debug("'%s': initializing %s transition\n", patch->mod->name, |
| klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); |
| |
| /* |
| * Initialize all tasks to the initial patch state to prepare them for |
| * switching to the target state. |
| */ |
| read_lock(&tasklist_lock); |
| for_each_process_thread(g, task) { |
| WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); |
| task->patch_state = initial_state; |
| } |
| read_unlock(&tasklist_lock); |
| |
| /* |
| * Ditto for the idle "swapper" tasks. |
| */ |
| for_each_possible_cpu(cpu) { |
| task = idle_task(cpu); |
| WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); |
| task->patch_state = initial_state; |
| } |
| |
| /* |
| * Enforce the order of the task->patch_state initializations and the |
| * func->transition updates to ensure that klp_ftrace_handler() doesn't |
| * see a func in transition with a task->patch_state of KLP_UNDEFINED. |
| * |
| * Also enforce the order of the klp_target_state write and future |
| * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't |
| * set a task->patch_state to KLP_UNDEFINED. |
| */ |
| smp_wmb(); |
| |
| /* |
| * Set the func transition states so klp_ftrace_handler() will know to |
| * switch to the transition logic. |
| * |
| * When patching, the funcs aren't yet in the func_stack and will be |
| * made visible to the ftrace handler shortly by the calls to |
| * klp_patch_object(). |
| * |
| * When unpatching, the funcs are already in the func_stack and so are |
| * already visible to the ftrace handler. |
| */ |
| klp_for_each_object(patch, obj) |
| klp_for_each_func(obj, func) |
| func->transition = true; |
| } |
| |
| /* |
| * This function can be called in the middle of an existing transition to |
| * reverse the direction of the target patch state. This can be done to |
| * effectively cancel an existing enable or disable operation if there are any |
| * tasks which are stuck in the initial patch state. |
| */ |
| void klp_reverse_transition(void) |
| { |
| unsigned int cpu; |
| struct task_struct *g, *task; |
| |
| pr_debug("'%s': reversing transition from %s\n", |
| klp_transition_patch->mod->name, |
| klp_target_state == KLP_PATCHED ? "patching to unpatching" : |
| "unpatching to patching"); |
| |
| klp_transition_patch->enabled = !klp_transition_patch->enabled; |
| |
| klp_target_state = !klp_target_state; |
| |
| /* |
| * Clear all TIF_PATCH_PENDING flags to prevent races caused by |
| * klp_update_patch_state() running in parallel with |
| * klp_start_transition(). |
| */ |
| read_lock(&tasklist_lock); |
| for_each_process_thread(g, task) |
| clear_tsk_thread_flag(task, TIF_PATCH_PENDING); |
| read_unlock(&tasklist_lock); |
| |
| for_each_possible_cpu(cpu) |
| clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING); |
| |
| /* Let any remaining calls to klp_update_patch_state() complete */ |
| klp_synchronize_transition(); |
| |
| klp_start_transition(); |
| } |
| |
| /* Called from copy_process() during fork */ |
| void klp_copy_process(struct task_struct *child) |
| { |
| |
| /* |
| * The parent process may have gone through a KLP transition since |
| * the thread flag was copied in setup_thread_stack earlier. Bring |
| * the task flag up to date with the parent here. |
| * |
| * The operation is serialized against all klp_*_transition() |
| * operations by the tasklist_lock. The only exception is |
| * klp_update_patch_state(current), but we cannot race with |
| * that because we are current. |
| */ |
| if (test_tsk_thread_flag(current, TIF_PATCH_PENDING)) |
| set_tsk_thread_flag(child, TIF_PATCH_PENDING); |
| else |
| clear_tsk_thread_flag(child, TIF_PATCH_PENDING); |
| |
| child->patch_state = current->patch_state; |
| } |
| |
| /* |
| * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an |
| * existing transition to finish. |
| * |
| * NOTE: klp_update_patch_state(task) requires the task to be inactive or |
| * 'current'. This is not the case here and the consistency model could be |
| * broken. Administrator, who is the only one to execute the |
| * klp_force_transitions(), has to be aware of this. |
| */ |
| void klp_force_transition(void) |
| { |
| struct klp_patch *patch; |
| struct task_struct *g, *task; |
| unsigned int cpu; |
| |
| pr_warn("forcing remaining tasks to the patched state\n"); |
| |
| read_lock(&tasklist_lock); |
| for_each_process_thread(g, task) |
| klp_update_patch_state(task); |
| read_unlock(&tasklist_lock); |
| |
| for_each_possible_cpu(cpu) |
| klp_update_patch_state(idle_task(cpu)); |
| |
| /* Set forced flag for patches being removed. */ |
| if (klp_target_state == KLP_UNPATCHED) |
| klp_transition_patch->forced = true; |
| else if (klp_transition_patch->replace) { |
| klp_for_each_patch(patch) { |
| if (patch != klp_transition_patch) |
| patch->forced = true; |
| } |
| } |
| } |