Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching

Pull livepatch updates from Jiri Kosina:

 - a per-task consistency model is being added for architectures that
   support reliable stack dumping (extending this, currently rather
   trivial set, is currently in the works).

   This extends the nature of the types of patches that can be applied
   by live patching infrastructure. The code stems from the design
   proposal made [1] back in November 2014. It's a hybrid of SUSE's
   kGraft and RH's kpatch, combining advantages of both: it uses
   kGraft's per-task consistency and syscall barrier switching combined
   with kpatch's stack trace switching. There are also a number of
   fallback options which make it quite flexible.

   Most of the heavy lifting done by Josh Poimboeuf with help from
   Miroslav Benes and Petr Mladek

   [1] https://lkml.kernel.org/r/20141107140458.GA21774@suse.cz

 - module load time patch optimization from Zhou Chengming

 - a few assorted small fixes

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: add missing printk newlines
  livepatch: Cancel transition a safe way for immediate patches
  livepatch: Reduce the time of finding module symbols
  livepatch: make klp_mutex proper part of API
  livepatch: allow removal of a disabled patch
  livepatch: add /proc/<pid>/patch_state
  livepatch: change to a per-task consistency model
  livepatch: store function sizes
  livepatch: use kstrtobool() in enabled_store()
  livepatch: move patching functions into patch.c
  livepatch: remove unnecessary object loaded check
  livepatch: separate enabled and patched states
  livepatch/s390: add TIF_PATCH_PENDING thread flag
  livepatch/s390: reorganize TIF thread flag bits
  livepatch/powerpc: add TIF_PATCH_PENDING thread flag
  livepatch/x86: add TIF_PATCH_PENDING thread flag
  livepatch: create temporary klp_update_patch_state() stub
  x86/entry: define _TIF_ALLWORK_MASK flags explicitly
  stacktrace/x86: add function for detecting reliable stack traces

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() */
+}