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-rw-r--r--kernel/livepatch/transition.c543
1 files changed, 543 insertions, 0 deletions
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
new file mode 100644
index 000000000000..428533ec51b5
--- /dev/null
+++ b/kernel/livepatch/transition.c
@@ -0,0 +1,543 @@
+/*
+ * 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 "patch.h"
+#include "transition.h"
+#include "../sched/sched.h"
+
+#define MAX_STACK_ENTRIES 100
+#define STACK_ERR_BUF_SIZE 128
+
+extern struct mutex klp_mutex;
+
+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;
+
+ 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;
+
+ /* 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)
+{
+ klp_target_state = !klp_target_state;
+ 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() */
+}