diff options
Diffstat (limited to 'kernel/livepatch/transition.c')
| -rw-r--r-- | kernel/livepatch/transition.c | 553 |
1 files changed, 553 insertions, 0 deletions
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c new file mode 100644 index 000000000000..adc0cc64aa4b --- /dev/null +++ b/kernel/livepatch/transition.c @@ -0,0 +1,553 @@ +/* + * transition.c - Kernel Live Patching transition functions + * + * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version 2 + * of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see <http://www.gnu.org/licenses/>. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/cpu.h> +#include <linux/stacktrace.h> +#include "core.h" +#include "patch.h" +#include "transition.h" +#include "../sched/sched.h" + +#define MAX_STACK_ENTRIES 100 +#define STACK_ERR_BUF_SIZE 128 + +struct klp_patch *klp_transition_patch; + +static int klp_target_state = KLP_UNDEFINED; + +/* + * 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); + +/* + * 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; + bool immediate_func = false; + + 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. + */ + synchronize_rcu(); + } + + if (klp_transition_patch->immediate) + goto done; + + klp_for_each_object(klp_transition_patch, obj) { + klp_for_each_func(obj, func) { + func->transition = false; + if (func->immediate) + immediate_func = true; + } + } + + if (klp_target_state == KLP_UNPATCHED && !immediate_func) + module_put(klp_transition_patch->mod); + + /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ + if (klp_target_state == KLP_PATCHED) + synchronize_rcu(); + + 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; + } + +done: + 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; + + 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) +{ + rcu_read_lock(); + + /* + * 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); + + rcu_read_unlock(); +} + +/* + * 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, + struct stack_trace *trace) +{ + unsigned long func_addr, func_size, address; + struct klp_ops *ops; + int i; + + if (func->immediate) + return 0; + + for (i = 0; i < trace->nr_entries; i++) { + address = trace->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_addr); + + if (list_is_singular(&ops->func_stack)) { + /* original function */ + func_addr = func->old_addr; + 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, char *err_buf) +{ + static unsigned long entries[MAX_STACK_ENTRIES]; + struct stack_trace trace; + struct klp_object *obj; + struct klp_func *func; + int ret; + + trace.skip = 0; + trace.nr_entries = 0; + trace.max_entries = MAX_STACK_ENTRIES; + trace.entries = entries; + ret = save_stack_trace_tsk_reliable(task, &trace); + WARN_ON_ONCE(ret == -ENOSYS); + if (ret) { + snprintf(err_buf, STACK_ERR_BUF_SIZE, + "%s: %s:%d has an unreliable stack\n", + __func__, task->comm, task->pid); + return 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, &trace); + if (ret) { + snprintf(err_buf, STACK_ERR_BUF_SIZE, + "%s: %s:%d is sleeping on function %s\n", + __func__, task->comm, task->pid, + func->old_name); + return ret; + } + } + } + + 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) +{ + struct rq *rq; + struct rq_flags flags; + int ret; + bool success = false; + char err_buf[STACK_ERR_BUF_SIZE]; + + err_buf[0] = '\0'; + + /* 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. + */ + rq = task_rq_lock(task, &flags); + + if (task_running(rq, task) && task != current) { + snprintf(err_buf, STACK_ERR_BUF_SIZE, + "%s: %s:%d is running\n", __func__, task->comm, + task->pid); + goto done; + } + + ret = klp_check_stack(task, err_buf); + if (ret) + goto done; + + success = true; + + clear_tsk_thread_flag(task, TIF_PATCH_PENDING); + task->patch_state = klp_target_state; + +done: + task_rq_unlock(rq, task, &flags); + + /* + * Due to console deadlock issues, pr_debug() can't be used while + * holding the task rq lock. Instead we have to use a temporary buffer + * and print the debug message after releasing the lock. + */ + if (err_buf[0] != '\0') + pr_debug("%s", err_buf); + + return success; + +} + +/* + * 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; + bool complete = true; + + WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); + + /* + * If the patch can be applied or reverted immediately, skip the + * per-task transitions. + */ + if (klp_transition_patch->immediate) + goto success; + + /* + * 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. + */ + get_online_cpus(); + for_each_possible_cpu(cpu) { + task = idle_task(cpu); + if (cpu_online(cpu)) { + if (!klp_try_switch_task(task)) + complete = false; + } 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; + } + } + put_online_cpus(); + + if (!complete) { + /* + * 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; + } + +success: + pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name, + klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); + + /* we're done, now cleanup the data structures */ + klp_complete_transition(); +} + +/* + * 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': %s...\n", klp_transition_patch->mod->name, + klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); + + /* + * If the patch can be applied or reverted immediately, skip the + * per-task transitions. + */ + if (klp_transition_patch->immediate) + return; + + /* + * 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); + } +} + +/* + * 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; + + /* + * If the patch can be applied or reverted immediately, skip the + * per-task transitions. + */ + if (patch->immediate) + return; + + /* + * 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; + + 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 */ + synchronize_rcu(); + + 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() */ +} |