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