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-rw-r--r--Documentation/ABI/testing/sysfs-kernel-livepatch8
-rw-r--r--Documentation/livepatch/livepatch.txt186
-rw-r--r--include/linux/init_task.h9
-rw-r--r--include/linux/livepatch.h42
-rw-r--r--include/linux/sched.h3
-rw-r--r--kernel/fork.c3
-rw-r--r--kernel/livepatch/Makefile2
-rw-r--r--kernel/livepatch/core.c105
-rw-r--r--kernel/livepatch/patch.c59
-rw-r--r--kernel/livepatch/patch.h1
-rw-r--r--kernel/livepatch/transition.c543
-rw-r--r--kernel/livepatch/transition.h14
-rw-r--r--kernel/sched/idle.c4
-rw-r--r--samples/livepatch/livepatch-sample.c17
14 files changed, 947 insertions, 49 deletions
diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
index da87f43aec58..d5d39748382f 100644
--- a/Documentation/ABI/testing/sysfs-kernel-livepatch
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -25,6 +25,14 @@ Description:
code is currently applied. Writing 0 will disable the patch
while writing 1 will re-enable the patch.
+What: /sys/kernel/livepatch/<patch>/transition
+Date: Feb 2017
+KernelVersion: 4.12.0
+Contact: live-patching@vger.kernel.org
+Description:
+ An attribute which indicates whether the patch is currently in
+ transition.
+
What: /sys/kernel/livepatch/<patch>/<object>
Date: Nov 2014
KernelVersion: 3.19.0
diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index 9d2096c7160d..4f2aec8d4c12 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -72,7 +72,8 @@ example, they add a NULL pointer or a boundary check, fix a race by adding
a missing memory barrier, or add some locking around a critical section.
Most of these changes are self contained and the function presents itself
the same way to the rest of the system. In this case, the functions might
-be updated independently one by one.
+be updated independently one by one. (This can be done by setting the
+'immediate' flag in the klp_patch struct.)
But there are more complex fixes. For example, a patch might change
ordering of locking in multiple functions at the same time. Or a patch
@@ -86,20 +87,141 @@ or no data are stored in the modified structures at the moment.
The theory about how to apply functions a safe way is rather complex.
The aim is to define a so-called consistency model. It attempts to define
conditions when the new implementation could be used so that the system
-stays consistent. The theory is not yet finished. See the discussion at
-https://lkml.kernel.org/r/20141107140458.GA21774@suse.cz
-
-The current consistency model is very simple. It guarantees that either
-the old or the new function is called. But various functions get redirected
-one by one without any synchronization.
-
-In other words, the current implementation _never_ modifies the behavior
-in the middle of the call. It is because it does _not_ rewrite the entire
-function in the memory. Instead, the function gets redirected at the
-very beginning. But this redirection is used immediately even when
-some other functions from the same patch have not been redirected yet.
-
-See also the section "Limitations" below.
+stays consistent.
+
+Livepatch has a consistency model which is a hybrid of kGraft and
+kpatch: 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.
+
+Patches are applied on a per-task basis, when the task is deemed safe to
+switch over. When a patch is enabled, livepatch enters into a
+transition state where tasks are converging to the patched state.
+Usually this transition state can complete in a few seconds. The same
+sequence occurs when a patch is disabled, except the tasks converge from
+the patched state to the unpatched state.
+
+An interrupt handler inherits the patched state of the task it
+interrupts. The same is true for forked tasks: the child inherits the
+patched state of the parent.
+
+Livepatch uses several complementary approaches to determine when it's
+safe to patch tasks:
+
+1. The first and most effective approach is stack checking of sleeping
+ tasks. If no affected functions are on the stack of a given task,
+ the task is patched. In most cases this will patch most or all of
+ the tasks on the first try. Otherwise it'll keep trying
+ periodically. This option is only available if the architecture has
+ reliable stacks (HAVE_RELIABLE_STACKTRACE).
+
+2. The second approach, if needed, is kernel exit switching. A
+ task is switched when it returns to user space from a system call, a
+ user space IRQ, or a signal. It's useful in the following cases:
+
+ a) Patching I/O-bound user tasks which are sleeping on an affected
+ function. In this case you have to send SIGSTOP and SIGCONT to
+ force it to exit the kernel and be patched.
+ b) Patching CPU-bound user tasks. If the task is highly CPU-bound
+ then it will get patched the next time it gets interrupted by an
+ IRQ.
+ c) In the future it could be useful for applying patches for
+ architectures which don't yet have HAVE_RELIABLE_STACKTRACE. In
+ this case you would have to signal most of the tasks on the
+ system. However this isn't supported yet because there's
+ currently no way to patch kthreads without
+ HAVE_RELIABLE_STACKTRACE.
+
+3. For idle "swapper" tasks, since they don't ever exit the kernel, they
+ instead have a klp_update_patch_state() call in the idle loop which
+ allows them to be patched before the CPU enters the idle state.
+
+ (Note there's not yet such an approach for kthreads.)
+
+All the above approaches may be skipped by setting the 'immediate' flag
+in the 'klp_patch' struct, which will disable per-task consistency and
+patch all tasks immediately. This can be useful if the patch doesn't
+change any function or data semantics. Note that, even with this flag
+set, it's possible that some tasks may still be running with an old
+version of the function, until that function returns.
+
+There's also an 'immediate' flag in the 'klp_func' struct which allows
+you to specify that certain functions in the patch can be applied
+without per-task consistency. This might be useful if you want to patch
+a common function like schedule(), and the function change doesn't need
+consistency but the rest of the patch does.
+
+For architectures which don't have HAVE_RELIABLE_STACKTRACE, the user
+must set patch->immediate which causes all tasks to be patched
+immediately. This option should be used with care, only when the patch
+doesn't change any function or data semantics.
+
+In the future, architectures which don't have HAVE_RELIABLE_STACKTRACE
+may be allowed to use per-task consistency if we can come up with
+another way to patch kthreads.
+
+The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
+is in transition. Only a single patch (the topmost patch on the stack)
+can be in transition at a given time. A patch can remain in transition
+indefinitely, if any of the tasks are stuck in the initial patch state.
+
+A transition can be reversed and effectively canceled by writing the
+opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
+the transition is in progress. Then all the tasks will attempt to
+converge back to the original patch state.
+
+There's also a /proc/<pid>/patch_state file which can be used to
+determine which tasks are blocking completion of a patching operation.
+If a patch is in transition, this file shows 0 to indicate the task is
+unpatched and 1 to indicate it's patched. Otherwise, if no patch is in
+transition, it shows -1. Any tasks which are blocking the transition
+can be signaled with SIGSTOP and SIGCONT to force them to change their
+patched state.
+
+
+3.1 Adding consistency model support to new architectures
+---------------------------------------------------------
+
+For adding consistency model support to new architectures, there are a
+few options:
+
+1) Add CONFIG_HAVE_RELIABLE_STACKTRACE. This means porting objtool, and
+ for non-DWARF unwinders, also making sure there's a way for the stack
+ tracing code to detect interrupts on the stack.
+
+2) Alternatively, ensure that every kthread has a call to
+ klp_update_patch_state() in a safe location. Kthreads are typically
+ in an infinite loop which does some action repeatedly. The safe
+ location to switch the kthread's patch state would be at a designated
+ point in the loop where there are no locks taken and all data
+ structures are in a well-defined state.
+
+ The location is clear when using workqueues or the kthread worker
+ API. These kthreads process independent actions in a generic loop.
+
+ It's much more complicated with kthreads which have a custom loop.
+ There the safe location must be carefully selected on a case-by-case
+ basis.
+
+ In that case, arches without HAVE_RELIABLE_STACKTRACE would still be
+ able to use the non-stack-checking parts of the consistency model:
+
+ a) patching user tasks when they cross the kernel/user space
+ boundary; and
+
+ b) patching kthreads and idle tasks at their designated patch points.
+
+ This option isn't as good as option 1 because it requires signaling
+ user tasks and waking kthreads to patch them. But it could still be
+ a good backup option for those architectures which don't have
+ reliable stack traces yet.
+
+In the meantime, patches for such architectures can bypass the
+consistency model by setting klp_patch.immediate to true. This option
+is perfectly fine for patches which don't change the semantics of the
+patched functions. In practice, this is usable for ~90% of security
+fixes. Use of this option also means the patch can't be unloaded after
+it has been disabled.
4. Livepatch module
@@ -134,7 +256,7 @@ Documentation/livepatch/module-elf-format.txt for more details.
4.2. Metadata
-------------
+-------------
The patch is described by several structures that split the information
into three levels:
@@ -156,6 +278,9 @@ into three levels:
only for a particular object ( vmlinux or a kernel module ). Note that
kallsyms allows for searching symbols according to the object name.
+ There's also an 'immediate' flag which, when set, patches the
+ function immediately, bypassing the consistency model safety checks.
+
+ struct klp_object defines an array of patched functions (struct
klp_func) in the same object. Where the object is either vmlinux
(NULL) or a module name.
@@ -172,10 +297,13 @@ into three levels:
This structure handles all patched functions consistently and eventually,
synchronously. The whole patch is applied only when all patched
symbols are found. The only exception are symbols from objects
- (kernel modules) that have not been loaded yet. Also if a more complex
- consistency model is supported then a selected unit (thread,
- kernel as a whole) will see the new code from the entire patch
- only when it is in a safe state.
+ (kernel modules) that have not been loaded yet.
+
+ Setting the 'immediate' flag applies the patch to all tasks
+ immediately, bypassing the consistency model safety checks.
+
+ For more details on how the patch is applied on a per-task basis,
+ see the "Consistency model" section.
4.3. Livepatch module handling
@@ -239,9 +367,15 @@ Registered patches might be enabled either by calling klp_enable_patch() or
by writing '1' to /sys/kernel/livepatch/<name>/enabled. The system will
start using the new implementation of the patched functions at this stage.
-In particular, if an original function is patched for the first time, a
-function specific struct klp_ops is created and an universal ftrace handler
-is registered.
+When a patch is enabled, livepatch enters into a transition state where
+tasks are converging to the patched state. This is indicated by a value
+of '1' in /sys/kernel/livepatch/<name>/transition. Once all tasks have
+been patched, the 'transition' value changes to '0'. For more
+information about this process, see the "Consistency model" section.
+
+If an original function is patched for the first time, a function
+specific struct klp_ops is created and an universal ftrace handler is
+registered.
Functions might be patched multiple times. The ftrace handler is registered
only once for the given function. Further patches just add an entry to the
@@ -261,6 +395,12 @@ by writing '0' to /sys/kernel/livepatch/<name>/enabled. At this stage
either the code from the previously enabled patch or even the original
code gets used.
+When a patch is disabled, livepatch enters into a transition state where
+tasks are converging to the unpatched state. This is indicated by a
+value of '1' in /sys/kernel/livepatch/<name>/transition. Once all tasks
+have been unpatched, the 'transition' value changes to '0'. For more
+information about this process, see the "Consistency model" section.
+
Here all the functions (struct klp_func) associated with the to-be-disabled
patch are removed from the corresponding struct klp_ops. The ftrace handler
is unregistered and the struct klp_ops is freed when the func_stack list
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 91d9049f0039..5a791055b176 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -15,6 +15,7 @@
#include <linux/sched/autogroup.h>
#include <net/net_namespace.h>
#include <linux/sched/rt.h>
+#include <linux/livepatch.h>
#include <linux/mm_types.h>
#include <asm/thread_info.h>
@@ -202,6 +203,13 @@ extern struct cred init_cred;
# define INIT_KASAN(tsk)
#endif
+#ifdef CONFIG_LIVEPATCH
+# define INIT_LIVEPATCH(tsk) \
+ .patch_state = KLP_UNDEFINED,
+#else
+# define INIT_LIVEPATCH(tsk)
+#endif
+
#ifdef CONFIG_THREAD_INFO_IN_TASK
# define INIT_TASK_TI(tsk) \
.thread_info = INIT_THREAD_INFO(tsk), \
@@ -288,6 +296,7 @@ extern struct cred init_cred;
INIT_VTIME(tsk) \
INIT_NUMA_BALANCING(tsk) \
INIT_KASAN(tsk) \
+ INIT_LIVEPATCH(tsk) \
}
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 6602b34bed2b..ed90ad1605c1 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -28,18 +28,40 @@
#include <asm/livepatch.h>
+/* task patch states */
+#define KLP_UNDEFINED -1
+#define KLP_UNPATCHED 0
+#define KLP_PATCHED 1
+
/**
* struct klp_func - function structure for live patching
* @old_name: name of the function to be patched
* @new_func: pointer to the patched function code
* @old_sympos: a hint indicating which symbol position the old function
* can be found (optional)
+ * @immediate: patch the func immediately, bypassing safety mechanisms
* @old_addr: the address of the function being patched
* @kobj: kobject for sysfs resources
* @stack_node: list node for klp_ops func_stack list
* @old_size: size of the old function
* @new_size: size of the new function
* @patched: the func has been added to the klp_ops list
+ * @transition: the func is currently being applied or reverted
+ *
+ * The patched and transition variables define the func's patching state. When
+ * patching, a func is always in one of the following states:
+ *
+ * patched=0 transition=0: unpatched
+ * patched=0 transition=1: unpatched, temporary starting state
+ * patched=1 transition=1: patched, may be visible to some tasks
+ * patched=1 transition=0: patched, visible to all tasks
+ *
+ * And when unpatching, it goes in the reverse order:
+ *
+ * patched=1 transition=0: patched, visible to all tasks
+ * patched=1 transition=1: patched, may be visible to some tasks
+ * patched=0 transition=1: unpatched, temporary ending state
+ * patched=0 transition=0: unpatched
*/
struct klp_func {
/* external */
@@ -53,6 +75,7 @@ struct klp_func {
* in kallsyms for the given object is used.
*/
unsigned long old_sympos;
+ bool immediate;
/* internal */
unsigned long old_addr;
@@ -60,6 +83,7 @@ struct klp_func {
struct list_head stack_node;
unsigned long old_size, new_size;
bool patched;
+ bool transition;
};
/**
@@ -68,7 +92,7 @@ struct klp_func {
* @funcs: function entries for functions to be patched in the object
* @kobj: kobject for sysfs resources
* @mod: kernel module associated with the patched object
- * (NULL for vmlinux)
+ * (NULL for vmlinux)
* @patched: the object's funcs have been added to the klp_ops list
*/
struct klp_object {
@@ -86,6 +110,7 @@ struct klp_object {
* struct klp_patch - patch structure for live patching
* @mod: reference to the live patch module
* @objs: object entries for kernel objects to be patched
+ * @immediate: patch all funcs immediately, bypassing safety mechanisms
* @list: list node for global list of registered patches
* @kobj: kobject for sysfs resources
* @enabled: the patch is enabled (but operation may be incomplete)
@@ -94,6 +119,7 @@ struct klp_patch {
/* external */
struct module *mod;
struct klp_object *objs;
+ bool immediate;
/* internal */
struct list_head list;
@@ -121,13 +147,27 @@ void arch_klp_init_object_loaded(struct klp_patch *patch,
int klp_module_coming(struct module *mod);
void klp_module_going(struct module *mod);
+void klp_copy_process(struct task_struct *child);
void klp_update_patch_state(struct task_struct *task);
+static inline bool klp_patch_pending(struct task_struct *task)
+{
+ return test_tsk_thread_flag(task, TIF_PATCH_PENDING);
+}
+
+static inline bool klp_have_reliable_stack(void)
+{
+ return IS_ENABLED(CONFIG_STACKTRACE) &&
+ IS_ENABLED(CONFIG_HAVE_RELIABLE_STACKTRACE);
+}
+
#else /* !CONFIG_LIVEPATCH */
static inline int klp_module_coming(struct module *mod) { return 0; }
static inline void klp_module_going(struct module *mod) {}
+static inline bool klp_patch_pending(struct task_struct *task) { return false; }
static inline void klp_update_patch_state(struct task_struct *task) {}
+static inline void klp_copy_process(struct task_struct *child) {}
#endif /* CONFIG_LIVEPATCH */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d67eee84fd43..e11032010318 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1038,6 +1038,9 @@ struct task_struct {
/* A live task holds one reference: */
atomic_t stack_refcount;
#endif
+#ifdef CONFIG_LIVEPATCH
+ int patch_state;
+#endif
/* CPU-specific state of this task: */
struct thread_struct thread;
diff --git a/kernel/fork.c b/kernel/fork.c
index 6c463c80e93d..942cbcd07c18 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -87,6 +87,7 @@
#include <linux/compiler.h>
#include <linux/sysctl.h>
#include <linux/kcov.h>
+#include <linux/livepatch.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -1797,6 +1798,8 @@ static __latent_entropy struct task_struct *copy_process(
p->parent_exec_id = current->self_exec_id;
}
+ klp_copy_process(p);
+
spin_lock(&current->sighand->siglock);
/*
diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
index e136dad8ff7e..2b8bdb1925da 100644
--- a/kernel/livepatch/Makefile
+++ b/kernel/livepatch/Makefile
@@ -1,3 +1,3 @@
obj-$(CONFIG_LIVEPATCH) += livepatch.o
-livepatch-objs := core.o patch.o
+livepatch-objs := core.o patch.o transition.o
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 10ba3a1578bd..3dc3c9049690 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -31,22 +31,22 @@
#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
#include "patch.h"
+#include "transition.h"
/*
- * The klp_mutex protects the global lists and state transitions of any
- * structure reachable from them. References to any structure must be obtained
- * under mutex protection (except in klp_ftrace_handler(), which uses RCU to
- * ensure it gets consistent data).
+ * klp_mutex is a coarse lock which serializes access to klp data. All
+ * accesses to klp-related variables and structures must have mutex protection,
+ * except within the following functions which carefully avoid the need for it:
+ *
+ * - klp_ftrace_handler()
+ * - klp_update_patch_state()
*/
-static DEFINE_MUTEX(klp_mutex);
+DEFINE_MUTEX(klp_mutex);
static LIST_HEAD(klp_patches);
static struct kobject *klp_root_kobj;
-/* TODO: temporary stub */
-void klp_update_patch_state(struct task_struct *task) {}
-
static bool klp_is_module(struct klp_object *obj)
{
return obj->name;
@@ -85,7 +85,6 @@ static void klp_find_object_module(struct klp_object *obj)
mutex_unlock(&module_mutex);
}
-/* klp_mutex must be held by caller */
static bool klp_is_patch_registered(struct klp_patch *patch)
{
struct klp_patch *mypatch;
@@ -281,20 +280,27 @@ static int klp_write_object_relocations(struct module *pmod,
static int __klp_disable_patch(struct klp_patch *patch)
{
- struct klp_object *obj;
+ if (klp_transition_patch)
+ return -EBUSY;
/* enforce stacking: only the last enabled patch can be disabled */
if (!list_is_last(&patch->list, &klp_patches) &&
list_next_entry(patch, list)->enabled)
return -EBUSY;
- pr_notice("disabling patch '%s'\n", patch->mod->name);
+ klp_init_transition(patch, KLP_UNPATCHED);
- klp_for_each_object(patch, obj) {
- if (obj->patched)
- klp_unpatch_object(obj);
- }
+ /*
+ * Enforce the order of the func->transition writes in
+ * klp_init_transition() and the TIF_PATCH_PENDING writes in
+ * klp_start_transition(). In the rare case where klp_ftrace_handler()
+ * is called shortly after klp_update_patch_state() switches the task,
+ * this ensures the handler sees that func->transition is set.
+ */
+ smp_wmb();
+ klp_start_transition();
+ klp_try_complete_transition();
patch->enabled = false;
return 0;
@@ -337,6 +343,9 @@ static int __klp_enable_patch(struct klp_patch *patch)
struct klp_object *obj;
int ret;
+ if (klp_transition_patch)
+ return -EBUSY;
+
if (WARN_ON(patch->enabled))
return -EINVAL;
@@ -347,22 +356,36 @@ static int __klp_enable_patch(struct klp_patch *patch)
pr_notice("enabling patch '%s'\n", patch->mod->name);
+ klp_init_transition(patch, KLP_PATCHED);
+
+ /*
+ * Enforce the order of the func->transition writes in
+ * klp_init_transition() and the ops->func_stack writes in
+ * klp_patch_object(), so that klp_ftrace_handler() will see the
+ * func->transition updates before the handler is registered and the
+ * new funcs become visible to the handler.
+ */
+ smp_wmb();
+
klp_for_each_object(patch, obj) {
if (!klp_is_object_loaded(obj))
continue;
ret = klp_patch_object(obj);
- if (ret)
- goto unregister;
+ if (ret) {
+ pr_warn("failed to enable patch '%s'\n",
+ patch->mod->name);
+
+ klp_cancel_transition();
+ return ret;
+ }
}
+ klp_start_transition();
+ klp_try_complete_transition();
patch->enabled = true;
return 0;
-
-unregister:
- WARN_ON(__klp_disable_patch(patch));
- return ret;
}
/**
@@ -399,6 +422,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
* /sys/kernel/livepatch
* /sys/kernel/livepatch/<patch>
* /sys/kernel/livepatch/<patch>/enabled
+ * /sys/kernel/livepatch/<patch>/transition
* /sys/kernel/livepatch/<patch>/<object>
* /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
*/
@@ -424,7 +448,9 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
goto err;
}
- if (enabled) {
+ if (patch == klp_transition_patch) {
+ klp_reverse_transition();
+ } else if (enabled) {
ret = __klp_enable_patch(patch);
if (ret)
goto err;
@@ -452,9 +478,21 @@ static ssize_t enabled_show(struct kobject *kobj,
return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->enabled);
}
+static ssize_t transition_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ struct klp_patch *patch;
+
+ patch = container_of(kobj, struct klp_patch, kobj);
+ return snprintf(buf, PAGE_SIZE-1, "%d\n",
+ patch == klp_transition_patch);
+}
+
static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
+static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
static struct attribute *klp_patch_attrs[] = {
&enabled_kobj_attr.attr,
+ &transition_kobj_attr.attr,
NULL
};
@@ -544,6 +582,7 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
INIT_LIST_HEAD(&func->stack_node);
func->patched = false;
+ func->transition = false;
/* The format for the sysfs directory is <function,sympos> where sympos
* is the nth occurrence of this symbol in kallsyms for the patched
@@ -740,6 +779,16 @@ int klp_register_patch(struct klp_patch *patch)
return -ENODEV;
/*
+ * Architectures without reliable stack traces have to set
+ * patch->immediate because there's currently no way to patch kthreads
+ * with the consistency model.
+ */
+ if (!klp_have_reliable_stack() && !patch->immediate) {
+ pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
+ return -ENOSYS;
+ }
+
+ /*
* A reference is taken on the patch module to prevent it from being
* unloaded. Right now, we don't allow patch modules to unload since
* there is currently no method to determine if a thread is still
@@ -788,7 +837,11 @@ int klp_module_coming(struct module *mod)
goto err;
}
- if (!patch->enabled)
+ /*
+ * Only patch the module if the patch is enabled or is
+ * in transition.
+ */
+ if (!patch->enabled && patch != klp_transition_patch)
break;
pr_notice("applying patch '%s' to loading module '%s'\n",
@@ -845,7 +898,11 @@ void klp_module_going(struct module *mod)
if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
continue;
- if (patch->enabled) {
+ /*
+ * Only unpatch the module if the patch is enabled or
+ * is in transition.
+ */
+ if (patch->enabled || patch == klp_transition_patch) {
pr_notice("reverting patch '%s' on unloading module '%s'\n",
patch->mod->name, obj->mod->name);
klp_unpatch_object(obj);
diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
index 5efa2620851a..f8269036bf0b 100644
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -29,6 +29,7 @@
#include <linux/bug.h>
#include <linux/printk.h>
#include "patch.h"
+#include "transition.h"
static LIST_HEAD(klp_ops);
@@ -54,15 +55,64 @@ static void notrace klp_ftrace_handler(unsigned long ip,
{
struct klp_ops *ops;
struct klp_func *func;
+ int patch_state;
ops = container_of(fops, struct klp_ops, fops);
rcu_read_lock();
+
func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
stack_node);
+
+ /*
+ * func should never be NULL because preemption should be disabled here
+ * and unregister_ftrace_function() does the equivalent of a
+ * synchronize_sched() before the func_stack removal.
+ */
if (WARN_ON_ONCE(!func))
goto unlock;
+ /*
+ * In the enable path, enforce the order of the ops->func_stack and
+ * func->transition reads. The corresponding write barrier is in
+ * __klp_enable_patch().
+ *
+ * (Note that this barrier technically isn't needed in the disable
+ * path. In the rare case where klp_update_patch_state() runs before
+ * this handler, its TIF_PATCH_PENDING read and this func->transition
+ * read need to be ordered. But klp_update_patch_state() already
+ * enforces that.)
+ */
+ smp_rmb();
+
+ if (unlikely(func->transition)) {
+
+ /*
+ * Enforce the order of the func->transition and
+ * current->patch_state reads. Otherwise we could read an
+ * out-of-date task state and pick the wrong function. The
+ * corresponding write barrier is in klp_init_transition().
+ */
+ smp_rmb();
+
+ patch_state = current->patch_state;
+
+ WARN_ON_ONCE(patch_state == KLP_UNDEFINED);
+
+ if (patch_state == KLP_UNPATCHED) {
+ /*
+ * Use the previously patched version of the function.
+ * If no previous patches exist, continue with the
+ * original function.
+ */
+ func = list_entry_rcu(func->stack_node.next,
+ struct klp_func, stack_node);
+
+ if (&func->stack_node == &ops->func_stack)
+ goto unlock;
+ }
+ }
+
klp_arch_set_pc(regs, (unsigned long)func->new_func);
unlock:
rcu_read_unlock();
@@ -211,3 +261,12 @@ int klp_patch_object(struct klp_object *obj)
return 0;
}
+
+void klp_unpatch_objects(struct klp_patch *patch)
+{
+ struct klp_object *obj;
+
+ klp_for_each_object(patch, obj)
+ if (obj->patched)
+ klp_unpatch_object(obj);
+}
diff --git a/kernel/livepatch/patch.h b/kernel/livepatch/patch.h
index 2d0cce02dade..0db227170c36 100644
--- a/kernel/livepatch/patch.h
+++ b/kernel/livepatch/patch.h
@@ -28,5 +28,6 @@ struct klp_ops *klp_find_ops(unsigned long old_addr);
int klp_patch_object(struct klp_object *obj);
void klp_unpatch_object(struct klp_object *obj);
+void klp_unpatch_objects(struct klp_patch *patch);
#endif /* _LIVEPATCH_PATCH_H */
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() */
+}
diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
new file mode 100644
index 000000000000..ce09b326546c
--- /dev/null
+++ b/kernel/livepatch/transition.h
@@ -0,0 +1,14 @@
+#ifndef _LIVEPATCH_TRANSITION_H
+#define _LIVEPATCH_TRANSITION_H
+
+#include <linux/livepatch.h>
+
+extern struct klp_patch *klp_transition_patch;
+
+void klp_init_transition(struct klp_patch *patch, int state);
+void klp_cancel_transition(void);
+void klp_start_transition(void);
+void klp_try_complete_transition(void);
+void klp_reverse_transition(void);
+
+#endif /* _LIVEPATCH_TRANSITION_H */
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index ac6d5176463d..2a25a9ec2c6e 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -10,6 +10,7 @@
#include <linux/mm.h>
#include <linux/stackprotector.h>
#include <linux/suspend.h>
+#include <linux/livepatch.h>
#include <asm/tlb.h>
@@ -265,6 +266,9 @@ static void do_idle(void)
sched_ttwu_pending();
schedule_preempt_disabled();
+
+ if (unlikely(klp_patch_pending(current)))
+ klp_update_patch_state(current);
}
bool cpu_in_idle(unsigned long pc)
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
index e34f871e69b1..629e0dca0887 100644
--- a/samples/livepatch/livepatch-sample.c
+++ b/samples/livepatch/livepatch-sample.c
@@ -17,6 +17,8 @@
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/livepatch.h>
@@ -69,6 +71,21 @@ static int livepatch_init(void)
{
int ret;
+ if (!klp_have_reliable_stack() && !patch.immediate) {
+ /*
+ * WARNING: Be very careful when using 'patch.immediate' in
+ * your patches. It's ok to use it for simple patches like
+ * this, but for more complex patches which change function
+ * semantics, locking semantics, or data structures, it may not
+ * be safe. Use of this option will also prevent removal of
+ * the patch.
+ *
+ * See Documentation/livepatch/livepatch.txt for more details.
+ */
+ patch.immediate = true;
+ pr_notice("The consistency model isn't supported for your architecture. Bypassing safety mechanisms and applying the patch immediately.\n");
+ }
+
ret = klp_register_patch(&patch);
if (ret)
return ret;