Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 1741 insertions, 0 deletions

diff --git a/Documentation/livepatch/api.rst b/Documentation/livepatch/api.rst
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index 0000000000..78944b63d7
--- /dev/null
+++ b/Documentation/livepatch/api.rst
@@ -0,0 +1,30 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+Livepatching APIs
+=================
+
+Livepatch Enablement
+====================
+
+.. kernel-doc:: kernel/livepatch/core.c
+   :export:
+
+
+Shadow Variables
+================
+
+.. kernel-doc:: kernel/livepatch/shadow.c
+   :export:
+
+System State Changes
+====================
+
+.. kernel-doc:: kernel/livepatch/state.c
+   :export:
+
+Object Types
+============
+
+.. kernel-doc:: include/linux/livepatch.h
+   :identifiers: klp_patch klp_object klp_func klp_callbacks klp_state
diff --git a/Documentation/livepatch/callbacks.rst b/Documentation/livepatch/callbacks.rst
new file mode 100644
index 0000000000..470944aa86
--- /dev/null
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@@ -0,0 +1,133 @@
+======================
+(Un)patching Callbacks
+======================
+
+Livepatch (un)patch-callbacks provide a mechanism for livepatch modules
+to execute callback functions when a kernel object is (un)patched.  They
+can be considered a **power feature** that **extends livepatching abilities**
+to include:
+
+  - Safe updates to global data
+
+  - "Patches" to init and probe functions
+
+  - Patching otherwise unpatchable code (i.e. assembly)
+
+In most cases, (un)patch callbacks will need to be used in conjunction
+with memory barriers and kernel synchronization primitives, like
+mutexes/spinlocks, or even stop_machine(), to avoid concurrency issues.
+
+1. Motivation
+=============
+
+Callbacks differ from existing kernel facilities:
+
+  - Module init/exit code doesn't run when disabling and re-enabling a
+    patch.
+
+  - A module notifier can't stop a to-be-patched module from loading.
+
+Callbacks are part of the klp_object structure and their implementation
+is specific to that klp_object.  Other livepatch objects may or may not
+be patched, irrespective of the target klp_object's current state.
+
+2. Callback types
+=================
+
+Callbacks can be registered for the following livepatch actions:
+
+  * Pre-patch
+                 - before a klp_object is patched
+
+  * Post-patch
+                 - after a klp_object has been patched and is active
+                   across all tasks
+
+  * Pre-unpatch
+                 - before a klp_object is unpatched (ie, patched code is
+                   active), used to clean up post-patch callback
+                   resources
+
+  * Post-unpatch
+                 - after a klp_object has been patched, all code has
+                   been restored and no tasks are running patched code,
+                   used to cleanup pre-patch callback resources
+
+3. How it works
+===============
+
+Each callback is optional, omitting one does not preclude specifying any
+other.  However, the livepatching core executes the handlers in
+symmetry: pre-patch callbacks have a post-unpatch counterpart and
+post-patch callbacks have a pre-unpatch counterpart.  An unpatch
+callback will only be executed if its corresponding patch callback was
+executed.  Typical use cases pair a patch handler that acquires and
+configures resources with an unpatch handler tears down and releases
+those same resources.
+
+A callback is only executed if its host klp_object is loaded.  For
+in-kernel vmlinux targets, this means that callbacks will always execute
+when a livepatch is enabled/disabled.  For patch target kernel modules,
+callbacks will only execute if the target module is loaded.  When a
+module target is (un)loaded, its callbacks will execute only if the
+livepatch module is enabled.
+
+The pre-patch callback, if specified, is expected to return a status
+code (0 for success, -ERRNO on error).  An error status code indicates
+to the livepatching core that patching of the current klp_object is not
+safe and to stop the current patching request.  (When no pre-patch
+callback is provided, the transition is assumed to be safe.)  If a
+pre-patch callback returns failure, the kernel's module loader will:
+
+  - Refuse to load a livepatch, if the livepatch is loaded after
+    targeted code.
+
+    or:
+
+  - Refuse to load a module, if the livepatch was already successfully
+    loaded.
+
+No post-patch, pre-unpatch, or post-unpatch callbacks will be executed
+for a given klp_object if the object failed to patch, due to a failed
+pre_patch callback or for any other reason.
+
+If a patch transition is reversed, no pre-unpatch handlers will be run
+(this follows the previously mentioned symmetry -- pre-unpatch callbacks
+will only occur if their corresponding post-patch callback executed).
+
+If the object did successfully patch, but the patch transition never
+started for some reason (e.g., if another object failed to patch),
+only the post-unpatch callback will be called.
+
+4. Use cases
+============
+
+Sample livepatch modules demonstrating the callback API can be found in
+samples/livepatch/ directory.  These samples were modified for use in
+kselftests and can be found in the lib/livepatch directory.
+
+Global data update
+------------------
+
+A pre-patch callback can be useful to update a global variable.  For
+example, 75ff39ccc1bd ("tcp: make challenge acks less predictable")
+changes a global sysctl, as well as patches the tcp_send_challenge_ack()
+function.
+
+In this case, if we're being super paranoid, it might make sense to
+patch the data *after* patching is complete with a post-patch callback,
+so that tcp_send_challenge_ack() could first be changed to read
+sysctl_tcp_challenge_ack_limit with READ_ONCE.
+
+__init and probe function patches support
+-----------------------------------------
+
+Although __init and probe functions are not directly livepatch-able, it
+may be possible to implement similar updates via pre/post-patch
+callbacks.
+
+The commit ``48900cb6af42 ("virtio-net: drop NETIF_F_FRAGLIST")`` change the way that
+virtnet_probe() initialized its driver's net_device features.  A
+pre/post-patch callback could iterate over all such devices, making a
+similar change to their hw_features value.  (Client functions of the
+value may need to be updated accordingly.)
diff --git a/Documentation/livepatch/cumulative-patches.rst b/Documentation/livepatch/cumulative-patches.rst
new file mode 100644
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--- /dev/null
+++ b/Documentation/livepatch/cumulative-patches.rst
@@ -0,0 +1,102 @@
+===================================
+Atomic Replace & Cumulative Patches
+===================================
+
+There might be dependencies between livepatches. If multiple patches need
+to do different changes to the same function(s) then we need to define
+an order in which the patches will be installed. And function implementations
+from any newer livepatch must be done on top of the older ones.
+
+This might become a maintenance nightmare. Especially when more patches
+modified the same function in different ways.
+
+An elegant solution comes with the feature called "Atomic Replace". It allows
+creation of so called "Cumulative Patches". They include all wanted changes
+from all older livepatches and completely replace them in one transition.
+
+Usage
+-----
+
+The atomic replace can be enabled by setting "replace" flag in struct klp_patch,
+for example::
+
+	static struct klp_patch patch = {
+		.mod = THIS_MODULE,
+		.objs = objs,
+		.replace = true,
+	};
+
+All processes are then migrated to use the code only from the new patch.
+Once the transition is finished, all older patches are automatically
+disabled.
+
+Ftrace handlers are transparently removed from functions that are no
+longer modified by the new cumulative patch.
+
+As a result, the livepatch authors might maintain sources only for one
+cumulative patch. It helps to keep the patch consistent while adding or
+removing various fixes or features.
+
+Users could keep only the last patch installed on the system after
+the transition to has finished. It helps to clearly see what code is
+actually in use. Also the livepatch might then be seen as a "normal"
+module that modifies the kernel behavior. The only difference is that
+it can be updated at runtime without breaking its functionality.
+
+
+Features
+--------
+
+The atomic replace allows:
+
+  - Atomically revert some functions in a previous patch while
+    upgrading other functions.
+
+  - Remove eventual performance impact caused by core redirection
+    for functions that are no longer patched.
+
+  - Decrease user confusion about dependencies between livepatches.
+
+
+Limitations:
+------------
+
+  - Once the operation finishes, there is no straightforward way
+    to reverse it and restore the replaced patches atomically.
+
+    A good practice is to set .replace flag in any released livepatch.
+    Then re-adding an older livepatch is equivalent to downgrading
+    to that patch. This is safe as long as the livepatches do _not_ do
+    extra modifications in (un)patching callbacks or in the module_init()
+    or module_exit() functions, see below.
+
+    Also note that the replaced patch can be removed and loaded again
+    only when the transition was not forced.
+
+
+  - Only the (un)patching callbacks from the _new_ cumulative livepatch are
+    executed. Any callbacks from the replaced patches are ignored.
+
+    In other words, the cumulative patch is responsible for doing any actions
+    that are necessary to properly replace any older patch.
+
+    As a result, it might be dangerous to replace newer cumulative patches by
+    older ones. The old livepatches might not provide the necessary callbacks.
+
+    This might be seen as a limitation in some scenarios. But it makes life
+    easier in many others. Only the new cumulative livepatch knows what
+    fixes/features are added/removed and what special actions are necessary
+    for a smooth transition.
+
+    In any case, it would be a nightmare to think about the order of
+    the various callbacks and their interactions if the callbacks from all
+    enabled patches were called.
+
+
+  - There is no special handling of shadow variables. Livepatch authors
+    must create their own rules how to pass them from one cumulative
+    patch to the other. Especially that they should not blindly remove
+    them in module_exit() functions.
+
+    A good practice might be to remove shadow variables in the post-unpatch
+    callback. It is called only when the livepatch is properly disabled.
diff --git a/Documentation/livepatch/index.rst b/Documentation/livepatch/index.rst
new file mode 100644
index 0000000000..cebf1c71d4
--- /dev/null
+++ b/Documentation/livepatch/index.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+Kernel Livepatching
+===================
+
+.. toctree::
+    :maxdepth: 1
+
+    livepatch
+    callbacks
+    cumulative-patches
+    module-elf-format
+    shadow-vars
+    system-state
+    reliable-stacktrace
+    api
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`
diff --git a/Documentation/livepatch/livepatch.rst b/Documentation/livepatch/livepatch.rst
new file mode 100644
index 0000000000..68e3651e8a
--- /dev/null
+++ b/Documentation/livepatch/livepatch.rst
@@ -0,0 +1,448 @@
+=========
+Livepatch
+=========
+
+This document outlines basic information about kernel livepatching.
+
+.. Table of Contents:
+
+.. contents:: :local:
+
+
+1. Motivation
+=============
+
+There are many situations where users are reluctant to reboot a system. It may
+be because their system is performing complex scientific computations or under
+heavy load during peak usage. In addition to keeping systems up and running,
+users want to also have a stable and secure system. Livepatching gives users
+both by allowing for function calls to be redirected; thus, fixing critical
+functions without a system reboot.
+
+
+2. Kprobes, Ftrace, Livepatching
+================================
+
+There are multiple mechanisms in the Linux kernel that are directly related
+to redirection of code execution; namely: kernel probes, function tracing,
+and livepatching:
+
+  - The kernel probes are the most generic. The code can be redirected by
+    putting a breakpoint instruction instead of any instruction.
+
+  - The function tracer calls the code from a predefined location that is
+    close to the function entry point. This location is generated by the
+    compiler using the '-pg' gcc option.
+
+  - Livepatching typically needs to redirect the code at the very beginning
+    of the function entry before the function parameters or the stack
+    are in any way modified.
+
+All three approaches need to modify the existing code at runtime. Therefore
+they need to be aware of each other and not step over each other's toes.
+Most of these problems are solved by using the dynamic ftrace framework as
+a base. A Kprobe is registered as a ftrace handler when the function entry
+is probed, see CONFIG_KPROBES_ON_FTRACE. Also an alternative function from
+a live patch is called with the help of a custom ftrace handler. But there are
+some limitations, see below.
+
+
+3. Consistency model
+====================
+
+Functions are there for a reason. They take some input parameters, get or
+release locks, read, process, and even write some data in a defined way,
+have return values. In other words, each function has a defined semantic.
+
+Many fixes do not change the semantic of the modified functions. For
+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.
+
+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
+might exchange meaning of some temporary structures and update
+all the relevant functions. In this case, the affected unit
+(thread, whole kernel) need to start using all new versions of
+the functions at the same time. Also the switch must happen only
+when it is safe to do so, e.g. when the affected locks are released
+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.
+
+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.
+
+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.)
+
+Architectures which don't have HAVE_RELIABLE_STACKTRACE solely rely on
+the second approach. It's highly likely that some tasks may still be
+running with an old version of the function, until that function
+returns. In this case you would have to signal the tasks. This
+especially applies to kthreads. They may not be woken up and would need
+to be forced. See below for more information.
+
+Unless we can come up with another way to patch kthreads, architectures
+without HAVE_RELIABLE_STACKTRACE are not considered fully supported by
+the kernel livepatching.
+
+The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
+is in transition.  Only a single patch 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. This may be harmful to the system though. Sending a fake signal
+to all remaining blocking tasks is a better alternative. No proper signal is
+actually delivered (there is no data in signal pending structures). Tasks are
+interrupted or woken up, and forced to change their patched state. The fake
+signal is automatically sent every 15 seconds.
+
+Administrator can also affect a transition through
+/sys/kernel/livepatch/<patch>/force attribute. Writing 1 there clears
+TIF_PATCH_PENDING flag of all tasks and thus forces the tasks to the patched
+state. Important note! The force attribute is intended for cases when the
+transition gets stuck for a long time because of a blocking task. Administrator
+is expected to collect all necessary data (namely stack traces of such blocking
+tasks) and request a clearance from a patch distributor to force the transition.
+Unauthorized usage may cause harm to the system. It depends on the nature of the
+patch, which functions are (un)patched, and which functions the blocking tasks
+are sleeping in (/proc/<pid>/stack may help here). Removal (rmmod) of patch
+modules is permanently disabled when the force feature is used. It cannot be
+guaranteed there is no task sleeping in such module. It implies unbounded
+reference count if a patch module is disabled and enabled in a loop.
+
+Moreover, the usage of force may also affect future applications of live
+patches and cause even more harm to the system. Administrator should first
+consider to simply cancel a transition (see above). If force is used, reboot
+should be planned and no more live patches applied.
+
+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.
+
+
+4. Livepatch module
+===================
+
+Livepatches are distributed using kernel modules, see
+samples/livepatch/livepatch-sample.c.
+
+The module includes a new implementation of functions that we want
+to replace. In addition, it defines some structures describing the
+relation between the original and the new implementation. Then there
+is code that makes the kernel start using the new code when the livepatch
+module is loaded. Also there is code that cleans up before the
+livepatch module is removed. All this is explained in more details in
+the next sections.
+
+
+4.1. New functions
+------------------
+
+New versions of functions are typically just copied from the original
+sources. A good practice is to add a prefix to the names so that they
+can be distinguished from the original ones, e.g. in a backtrace. Also
+they can be declared as static because they are not called directly
+and do not need the global visibility.
+
+The patch contains only functions that are really modified. But they
+might want to access functions or data from the original source file
+that may only be locally accessible. This can be solved by a special
+relocation section in the generated livepatch module, see
+Documentation/livepatch/module-elf-format.rst for more details.
+
+
+4.2. Metadata
+-------------
+
+The patch is described by several structures that split the information
+into three levels:
+
+  - struct klp_func is defined for each patched function. It describes
+    the relation between the original and the new implementation of a
+    particular function.
+
+    The structure includes the name, as a string, of the original function.
+    The function address is found via kallsyms at runtime.
+
+    Then it includes the address of the new function. It is defined
+    directly by assigning the function pointer. Note that the new
+    function is typically defined in the same source file.
+
+    As an optional parameter, the symbol position in the kallsyms database can
+    be used to disambiguate functions of the same name. This is not the
+    absolute position in the database, but rather the order it has been found
+    only for a particular object ( vmlinux or a kernel module ). Note that
+    kallsyms allows for searching symbols according to the object name.
+
+  - 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.
+
+    The structure helps to group and handle functions for each object
+    together. Note that patched modules might be loaded later than
+    the patch itself and the relevant functions might be patched
+    only when they are available.
+
+
+  - struct klp_patch defines an array of patched objects (struct
+    klp_object).
+
+    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.
+
+    For more details on how the patch is applied on a per-task basis,
+    see the "Consistency model" section.
+
+
+5. Livepatch life-cycle
+=======================
+
+Livepatching can be described by five basic operations:
+loading, enabling, replacing, disabling, removing.
+
+Where the replacing and the disabling operations are mutually
+exclusive. They have the same result for the given patch but
+not for the system.
+
+
+5.1. Loading
+------------
+
+The only reasonable way is to enable the patch when the livepatch kernel
+module is being loaded. For this, klp_enable_patch() has to be called
+in the module_init() callback. There are two main reasons:
+
+First, only the module has an easy access to the related struct klp_patch.
+
+Second, the error code might be used to refuse loading the module when
+the patch cannot get enabled.
+
+
+5.2. Enabling
+-------------
+
+The livepatch gets enabled by calling klp_enable_patch() from
+the module_init() callback. The system will start using the new
+implementation of the patched functions at this stage.
+
+First, the addresses of the patched functions are found according to their
+names. The special relocations, mentioned in the section "New functions",
+are applied. The relevant entries are created under
+/sys/kernel/livepatch/<name>. The patch is rejected when any above
+operation fails.
+
+Second, livepatch enters into a transition state where tasks are converging
+to the patched state. 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\ [#]_. This stage is indicated by a value of '1'
+in /sys/kernel/livepatch/<name>/transition. For more information about
+this process, see the "Consistency model" section.
+
+Finally, once all tasks have been patched, the 'transition' value changes
+to '0'.
+
+.. [#]
+
+    Note that functions might be patched multiple times. The ftrace handler
+    is registered only once for a given function. Further patches just add
+    an entry to the list (see field `func_stack`) of the struct klp_ops.
+    The right implementation is selected by the ftrace handler, see
+    the "Consistency model" section.
+
+    That said, it is highly recommended to use cumulative livepatches
+    because they help keeping the consistency of all changes. In this case,
+    functions might be patched two times only during the transition period.
+
+
+5.3. Replacing
+--------------
+
+All enabled patches might get replaced by a cumulative patch that
+has the .replace flag set.
+
+Once the new patch is enabled and the 'transition' finishes then
+all the functions (struct klp_func) associated with the replaced
+patches are removed from the corresponding struct klp_ops. Also
+the ftrace handler is unregistered and the struct klp_ops is
+freed when the related function is not modified by the new patch
+and func_stack list becomes empty.
+
+See Documentation/livepatch/cumulative-patches.rst for more details.
+
+
+5.4. Disabling
+--------------
+
+Enabled patches might get disabled by writing '0' to
+/sys/kernel/livepatch/<name>/enabled.
+
+First, livepatch enters into a transition state where tasks are converging
+to the unpatched state. The system starts using either the code from
+the previously enabled patch or even the original one. This stage is
+indicated by a value of '1' in /sys/kernel/livepatch/<name>/transition.
+For more information about this process, see the "Consistency model"
+section.
+
+Second, once all tasks have been unpatched, the 'transition' value changes
+to '0'. 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
+becomes empty.
+
+Third, the sysfs interface is destroyed.
+
+
+5.5. Removing
+-------------
+
+Module removal is only safe when there are no users of functions provided
+by the module. This is the reason why the force feature permanently
+disables the removal. Only when the system is successfully transitioned
+to a new patch state (patched/unpatched) without being forced it is
+guaranteed that no task sleeps or runs in the old code.
+
+
+6. Sysfs
+========
+
+Information about the registered patches can be found under
+/sys/kernel/livepatch. The patches could be enabled and disabled
+by writing there.
+
+/sys/kernel/livepatch/<patch>/force attributes allow administrator to affect a
+patching operation.
+
+See Documentation/ABI/testing/sysfs-kernel-livepatch for more details.
+
+
+7. Limitations
+==============
+
+The current Livepatch implementation has several limitations:
+
+  - Only functions that can be traced could be patched.
+
+    Livepatch is based on the dynamic ftrace. In particular, functions
+    implementing ftrace or the livepatch ftrace handler could not be
+    patched. Otherwise, the code would end up in an infinite loop. A
+    potential mistake is prevented by marking the problematic functions
+    by "notrace".
+
+
+
+  - Livepatch works reliably only when the dynamic ftrace is located at
+    the very beginning of the function.
+
+    The function need to be redirected before the stack or the function
+    parameters are modified in any way. For example, livepatch requires
+    using -fentry gcc compiler option on x86_64.
+
+    One exception is the PPC port. It uses relative addressing and TOC.
+    Each function has to handle TOC and save LR before it could call
+    the ftrace handler. This operation has to be reverted on return.
+    Fortunately, the generic ftrace code has the same problem and all
+    this is handled on the ftrace level.
+
+
+  - Kretprobes using the ftrace framework conflict with the patched
+    functions.
+
+    Both kretprobes and livepatches use a ftrace handler that modifies
+    the return address. The first user wins. Either the probe or the patch
+    is rejected when the handler is already in use by the other.
+
+
+  - Kprobes in the original function are ignored when the code is
+    redirected to the new implementation.
+
+    There is a work in progress to add warnings about this situation.
diff --git a/Documentation/livepatch/module-elf-format.rst b/Documentation/livepatch/module-elf-format.rst
new file mode 100644
index 0000000000..a03ed02ec5
--- /dev/null
+++ b/Documentation/livepatch/module-elf-format.rst
@@ -0,0 +1,302 @@
+===========================
+Livepatch module ELF format
+===========================
+
+This document outlines the ELF format requirements that livepatch modules must follow.
+
+
+.. Table of Contents
+
+.. contents:: :local:
+
+
+1. Background and motivation
+============================
+
+Formerly, livepatch required separate architecture-specific code to write
+relocations. However, arch-specific code to write relocations already
+exists in the module loader, so this former approach produced redundant
+code. So, instead of duplicating code and re-implementing what the module
+loader can already do, livepatch leverages existing code in the module
+loader to perform the all the arch-specific relocation work. Specifically,
+livepatch reuses the apply_relocate_add() function in the module loader to
+write relocations. The patch module ELF format described in this document
+enables livepatch to be able to do this. The hope is that this will make
+livepatch more easily portable to other architectures and reduce the amount
+of arch-specific code required to port livepatch to a particular
+architecture.
+
+Since apply_relocate_add() requires access to a module's section header
+table, symbol table, and relocation section indices, ELF information is
+preserved for livepatch modules (see section 5). Livepatch manages its own
+relocation sections and symbols, which are described in this document. The
+ELF constants used to mark livepatch symbols and relocation sections were
+selected from OS-specific ranges according to the definitions from glibc.
+
+Why does livepatch need to write its own relocations?
+-----------------------------------------------------
+A typical livepatch module contains patched versions of functions that can
+reference non-exported global symbols and non-included local symbols.
+Relocations referencing these types of symbols cannot be left in as-is
+since the kernel module loader cannot resolve them and will therefore
+reject the livepatch module. Furthermore, we cannot apply relocations that
+affect modules not yet loaded at patch module load time (e.g. a patch to a
+driver that is not loaded). Formerly, livepatch solved this problem by
+embedding special "dynrela" (dynamic rela) sections in the resulting patch
+module ELF output. Using these dynrela sections, livepatch could resolve
+symbols while taking into account its scope and what module the symbol
+belongs to, and then manually apply the dynamic relocations. However this
+approach required livepatch to supply arch-specific code in order to write
+these relocations. In the new format, livepatch manages its own SHT_RELA
+relocation sections in place of dynrela sections, and the symbols that the
+relas reference are special livepatch symbols (see section 2 and 3). The
+arch-specific livepatch relocation code is replaced by a call to
+apply_relocate_add().
+
+2. Livepatch modinfo field
+==========================
+
+Livepatch modules are required to have the "livepatch" modinfo attribute.
+See the sample livepatch module in samples/livepatch/ for how this is done.
+
+Livepatch modules can be identified by users by using the 'modinfo' command
+and looking for the presence of the "livepatch" field. This field is also
+used by the kernel module loader to identify livepatch modules.
+
+Example:
+--------
+
+**Modinfo output:**
+
+::
+
+	% modinfo livepatch-meminfo.ko
+	filename:		livepatch-meminfo.ko
+	livepatch:		Y
+	license:		GPL
+	depends:
+	vermagic:		4.3.0+ SMP mod_unload
+
+3. Livepatch relocation sections
+================================
+
+A livepatch module manages its own ELF relocation sections to apply
+relocations to modules as well as to the kernel (vmlinux) at the
+appropriate time. For example, if a patch module patches a driver that is
+not currently loaded, livepatch will apply the corresponding livepatch
+relocation section(s) to the driver once it loads.
+
+Each "object" (e.g. vmlinux, or a module) within a patch module may have
+multiple livepatch relocation sections associated with it (e.g. patches to
+multiple functions within the same object). There is a 1-1 correspondence
+between a livepatch relocation section and the target section (usually the
+text section of a function) to which the relocation(s) apply. It is
+also possible for a livepatch module to have no livepatch relocation
+sections, as in the case of the sample livepatch module (see
+samples/livepatch).
+
+Since ELF information is preserved for livepatch modules (see Section 5), a
+livepatch relocation section can be applied simply by passing in the
+appropriate section index to apply_relocate_add(), which then uses it to
+access the relocation section and apply the relocations.
+
+Every symbol referenced by a rela in a livepatch relocation section is a
+livepatch symbol. These must be resolved before livepatch can call
+apply_relocate_add(). See Section 3 for more information.
+
+3.1 Livepatch relocation section format
+=======================================
+
+Livepatch relocation sections must be marked with the SHF_RELA_LIVEPATCH
+section flag. See include/uapi/linux/elf.h for the definition. The module
+loader recognizes this flag and will avoid applying those relocation sections
+at patch module load time. These sections must also be marked with SHF_ALLOC,
+so that the module loader doesn't discard them on module load (i.e. they will
+be copied into memory along with the other SHF_ALLOC sections).
+
+The name of a livepatch relocation section must conform to the following
+format::
+
+  .klp.rela.objname.section_name
+  ^        ^^     ^ ^          ^
+  |________||_____| |__________|
+     [A]      [B]        [C]
+
+[A]
+  The relocation section name is prefixed with the string ".klp.rela."
+
+[B]
+  The name of the object (i.e. "vmlinux" or name of module) to
+  which the relocation section belongs follows immediately after the prefix.
+
+[C]
+  The actual name of the section to which this relocation section applies.
+
+Examples:
+---------
+
+**Livepatch relocation section names:**
+
+::
+
+  .klp.rela.ext4.text.ext4_attr_store
+  .klp.rela.vmlinux.text.cmdline_proc_show
+
+**`readelf --sections` output for a patch
+module that patches vmlinux and modules 9p, btrfs, ext4:**
+
+::
+
+  Section Headers:
+  [Nr] Name                          Type                    Address          Off    Size   ES Flg Lk Inf Al
+  [ snip ]
+  [29] .klp.rela.9p.text.caches.show RELA                    0000000000000000 002d58 0000c0 18 AIo 64   9  8
+  [30] .klp.rela.btrfs.text.btrfs.feature.attr.show RELA     0000000000000000 002e18 000060 18 AIo 64  11  8
+  [ snip ]
+  [34] .klp.rela.ext4.text.ext4.attr.store RELA              0000000000000000 002fd8 0000d8 18 AIo 64  13  8
+  [35] .klp.rela.ext4.text.ext4.attr.show RELA               0000000000000000 0030b0 000150 18 AIo 64  15  8
+  [36] .klp.rela.vmlinux.text.cmdline.proc.show RELA         0000000000000000 003200 000018 18 AIo 64  17  8
+  [37] .klp.rela.vmlinux.text.meminfo.proc.show RELA         0000000000000000 003218 0000f0 18 AIo 64  19  8
+  [ snip ]                                       ^                                             ^
+                                                 |                                             |
+                                                [*]                                           [*]
+
+[*]
+  Livepatch relocation sections are SHT_RELA sections but with a few special
+  characteristics. Notice that they are marked SHF_ALLOC ("A") so that they will
+  not be discarded when the module is loaded into memory, as well as with the
+  SHF_RELA_LIVEPATCH flag ("o" - for OS-specific).
+
+**`readelf --relocs` output for a patch module:**
+
+::
+
+  Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
+      Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
+  000000000000001f  0000005e00000002 R_X86_64_PC32          0000000000000000 .klp.sym.vmlinux.printk,0 - 4
+  0000000000000028  0000003d0000000b R_X86_64_32S           0000000000000000 .klp.sym.btrfs.btrfs_ktype,0 + 0
+  0000000000000036  0000003b00000002 R_X86_64_PC32          0000000000000000 .klp.sym.btrfs.can_modify_feature.isra.3,0 - 4
+  000000000000004c  0000004900000002 R_X86_64_PC32          0000000000000000 .klp.sym.vmlinux.snprintf,0 - 4
+  [ snip ]                                                                   ^
+                                                                             |
+                                                                            [*]
+
+[*]
+  Every symbol referenced by a relocation is a livepatch symbol.
+
+4. Livepatch symbols
+====================
+
+Livepatch symbols are symbols referred to by livepatch relocation sections.
+These are symbols accessed from new versions of functions for patched
+objects, whose addresses cannot be resolved by the module loader (because
+they are local or unexported global syms). Since the module loader only
+resolves exported syms, and not every symbol referenced by the new patched
+functions is exported, livepatch symbols were introduced. They are used
+also in cases where we cannot immediately know the address of a symbol when
+a patch module loads. For example, this is the case when livepatch patches
+a module that is not loaded yet. In this case, the relevant livepatch
+symbols are resolved simply when the target module loads. In any case, for
+any livepatch relocation section, all livepatch symbols referenced by that
+section must be resolved before livepatch can call apply_relocate_add() for
+that reloc section.
+
+Livepatch symbols must be marked with SHN_LIVEPATCH so that the module
+loader can identify and ignore them. Livepatch modules keep these symbols
+in their symbol tables, and the symbol table is made accessible through
+module->symtab.
+
+4.1 A livepatch module's symbol table
+=====================================
+Normally, a stripped down copy of a module's symbol table (containing only
+"core" symbols) is made available through module->symtab (See layout_symtab()
+in kernel/module/kallsyms.c). For livepatch modules, the symbol table copied
+into memory on module load must be exactly the same as the symbol table produced
+when the patch module was compiled. This is because the relocations in each
+livepatch relocation section refer to their respective symbols with their symbol
+indices, and the original symbol indices (and thus the symtab ordering) must be
+preserved in order for apply_relocate_add() to find the right symbol.
+
+For example, take this particular rela from a livepatch module:::
+
+  Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
+      Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
+  000000000000001f  0000005e00000002 R_X86_64_PC32          0000000000000000 .klp.sym.vmlinux.printk,0 - 4
+
+  This rela refers to the symbol '.klp.sym.vmlinux.printk,0', and the symbol index is encoded
+  in 'Info'. Here its symbol index is 0x5e, which is 94 in decimal, which refers to the
+  symbol index 94.
+  And in this patch module's corresponding symbol table, symbol index 94 refers to that very symbol:
+  [ snip ]
+  94: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.printk,0
+  [ snip ]
+
+4.2 Livepatch symbol format
+===========================
+
+Livepatch symbols must have their section index marked as SHN_LIVEPATCH, so
+that the module loader can identify them and not attempt to resolve them.
+See include/uapi/linux/elf.h for the actual definitions.
+
+Livepatch symbol names must conform to the following format::
+
+  .klp.sym.objname.symbol_name,sympos
+  ^       ^^     ^ ^         ^ ^
+  |_______||_____| |_________| |
+     [A]     [B]       [C]    [D]
+
+[A]
+  The symbol name is prefixed with the string ".klp.sym."
+
+[B]
+  The name of the object (i.e. "vmlinux" or name of module) to
+  which the symbol belongs follows immediately after the prefix.
+
+[C]
+  The actual name of the symbol.
+
+[D]
+  The position of the symbol in the object (as according to kallsyms)
+  This is used to differentiate duplicate symbols within the same
+  object. The symbol position is expressed numerically (0, 1, 2...).
+  The symbol position of a unique symbol is 0.
+
+Examples:
+---------
+
+**Livepatch symbol names:**
+
+::
+
+	.klp.sym.vmlinux.snprintf,0
+	.klp.sym.vmlinux.printk,0
+	.klp.sym.btrfs.btrfs_ktype,0
+
+**`readelf --symbols` output for a patch module:**
+
+::
+
+  Symbol table '.symtab' contains 127 entries:
+     Num:    Value          Size Type    Bind   Vis     Ndx         Name
+     [ snip ]
+      73: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.snprintf,0
+      74: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.capable,0
+      75: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.find_next_bit,0
+      76: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.si_swapinfo,0
+    [ snip ]                                               ^
+                                                           |
+                                                          [*]
+
+[*]
+  Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
+  "OS" means OS-specific.
+
+5. Symbol table and ELF section access
+======================================
+A livepatch module's symbol table is accessible through module->symtab.
+
+Since apply_relocate_add() requires access to a module's section headers,
+symbol table, and relocation section indices, ELF information is preserved for
+livepatch modules and is made accessible by the module loader through
+module->klp_info, which is a :c:type:`klp_modinfo` struct. When a livepatch module
+loads, this struct is filled in by the module loader.
diff --git a/Documentation/livepatch/reliable-stacktrace.rst b/Documentation/livepatch/reliable-stacktrace.rst
new file mode 100644
index 0000000000..8d950f3ffe
--- /dev/null
+++ b/Documentation/livepatch/reliable-stacktrace.rst
@@ -0,0 +1,309 @@
+===================
+Reliable Stacktrace
+===================
+
+This document outlines basic information about reliable stacktracing.
+
+.. Table of Contents:
+
+.. contents:: :local:
+
+1. Introduction
+===============
+
+The kernel livepatch consistency model relies on accurately identifying which
+functions may have live state and therefore may not be safe to patch. One way
+to identify which functions are live is to use a stacktrace.
+
+Existing stacktrace code may not always give an accurate picture of all
+functions with live state, and best-effort approaches which can be helpful for
+debugging are unsound for livepatching. Livepatching depends on architectures
+to provide a *reliable* stacktrace which ensures it never omits any live
+functions from a trace.
+
+
+2. Requirements
+===============
+
+Architectures must implement one of the reliable stacktrace functions.
+Architectures using CONFIG_ARCH_STACKWALK must implement
+'arch_stack_walk_reliable', and other architectures must implement
+'save_stack_trace_tsk_reliable'.
+
+Principally, the reliable stacktrace function must ensure that either:
+
+* The trace includes all functions that the task may be returned to, and the
+  return code is zero to indicate that the trace is reliable.
+
+* The return code is non-zero to indicate that the trace is not reliable.
+
+.. note::
+   In some cases it is legitimate to omit specific functions from the trace,
+   but all other functions must be reported. These cases are described in
+   further detail below.
+
+Secondly, the reliable stacktrace function must be robust to cases where
+the stack or other unwind state is corrupt or otherwise unreliable. The
+function should attempt to detect such cases and return a non-zero error
+code, and should not get stuck in an infinite loop or access memory in
+an unsafe way.  Specific cases are described in further detail below.
+
+
+3. Compile-time analysis
+========================
+
+To ensure that kernel code can be correctly unwound in all cases,
+architectures may need to verify that code has been compiled in a manner
+expected by the unwinder. For example, an unwinder may expect that
+functions manipulate the stack pointer in a limited way, or that all
+functions use specific prologue and epilogue sequences. Architectures
+with such requirements should verify the kernel compilation using
+objtool.
+
+In some cases, an unwinder may require metadata to correctly unwind.
+Where necessary, this metadata should be generated at build time using
+objtool.
+
+
+4. Considerations
+=================
+
+The unwinding process varies across architectures, their respective procedure
+call standards, and kernel configurations. This section describes common
+details that architectures should consider.
+
+4.1 Identifying successful termination
+--------------------------------------
+
+Unwinding may terminate early for a number of reasons, including:
+
+* Stack or frame pointer corruption.
+
+* Missing unwind support for an uncommon scenario, or a bug in the unwinder.
+
+* Dynamically generated code (e.g. eBPF) or foreign code (e.g. EFI runtime
+  services) not following the conventions expected by the unwinder.
+
+To ensure that this does not result in functions being omitted from the trace,
+even if not caught by other checks, it is strongly recommended that
+architectures verify that a stacktrace ends at an expected location, e.g.
+
+* Within a specific function that is an entry point to the kernel.
+
+* At a specific location on a stack expected for a kernel entry point.
+
+* On a specific stack expected for a kernel entry point (e.g. if the
+  architecture has separate task and IRQ stacks).
+
+4.2 Identifying unwindable code
+-------------------------------
+
+Unwinding typically relies on code following specific conventions (e.g.
+manipulating a frame pointer), but there can be code which may not follow these
+conventions and may require special handling in the unwinder, e.g.
+
+* Exception vectors and entry assembly.
+
+* Procedure Linkage Table (PLT) entries and veneer functions.
+
+* Trampoline assembly (e.g. ftrace, kprobes).
+
+* Dynamically generated code (e.g. eBPF, optprobe trampolines).
+
+* Foreign code (e.g. EFI runtime services).
+
+To ensure that such cases do not result in functions being omitted from a
+trace, it is strongly recommended that architectures positively identify code
+which is known to be reliable to unwind from, and reject unwinding from all
+other code.
+
+Kernel code including modules and eBPF can be distinguished from foreign code
+using '__kernel_text_address()'. Checking for this also helps to detect stack
+corruption.
+
+There are several ways an architecture may identify kernel code which is deemed
+unreliable to unwind from, e.g.
+
+* Placing such code into special linker sections, and rejecting unwinding from
+  any code in these sections.
+
+* Identifying specific portions of code using bounds information.
+
+4.3 Unwinding across interrupts and exceptions
+----------------------------------------------
+
+At function call boundaries the stack and other unwind state is expected to be
+in a consistent state suitable for reliable unwinding, but this may not be the
+case part-way through a function. For example, during a function prologue or
+epilogue a frame pointer may be transiently invalid, or during the function
+body the return address may be held in an arbitrary general purpose register.
+For some architectures this may change at runtime as a result of dynamic
+instrumentation.
+
+If an interrupt or other exception is taken while the stack or other unwind
+state is in an inconsistent state, it may not be possible to reliably unwind,
+and it may not be possible to identify whether such unwinding will be reliable.
+See below for examples.
+
+Architectures which cannot identify when it is reliable to unwind such cases
+(or where it is never reliable) must reject unwinding across exception
+boundaries. Note that it may be reliable to unwind across certain
+exceptions (e.g. IRQ) but unreliable to unwind across other exceptions
+(e.g. NMI).
+
+Architectures which can identify when it is reliable to unwind such cases (or
+have no such cases) should attempt to unwind across exception boundaries, as
+doing so can prevent unnecessarily stalling livepatch consistency checks and
+permits livepatch transitions to complete more quickly.
+
+4.4 Rewriting of return addresses
+---------------------------------
+
+Some trampolines temporarily modify the return address of a function in order
+to intercept when that function returns with a return trampoline, e.g.
+
+* An ftrace trampoline may modify the return address so that function graph
+  tracing can intercept returns.
+
+* A kprobes (or optprobes) trampoline may modify the return address so that
+  kretprobes can intercept returns.
+
+When this happens, the original return address will not be in its usual
+location. For trampolines which are not subject to live patching, where an
+unwinder can reliably determine the original return address and no unwind state
+is altered by the trampoline, the unwinder may report the original return
+address in place of the trampoline and report this as reliable. Otherwise, an
+unwinder must report these cases as unreliable.
+
+Special care is required when identifying the original return address, as this
+information is not in a consistent location for the duration of the entry
+trampoline or return trampoline. For example, considering the x86_64
+'return_to_handler' return trampoline:
+
+.. code-block:: none
+
+   SYM_CODE_START(return_to_handler)
+           UNWIND_HINT_UNDEFINED
+           subq  $24, %rsp
+
+           /* Save the return values */
+           movq %rax, (%rsp)
+           movq %rdx, 8(%rsp)
+           movq %rbp, %rdi
+
+           call ftrace_return_to_handler
+
+           movq %rax, %rdi
+           movq 8(%rsp), %rdx
+           movq (%rsp), %rax
+           addq $24, %rsp
+           JMP_NOSPEC rdi
+   SYM_CODE_END(return_to_handler)
+
+While the traced function runs its return address on the stack points to
+the start of return_to_handler, and the original return address is stored in
+the task's cur_ret_stack. During this time the unwinder can find the return
+address using ftrace_graph_ret_addr().
+
+When the traced function returns to return_to_handler, there is no longer a
+return address on the stack, though the original return address is still stored
+in the task's cur_ret_stack. Within ftrace_return_to_handler(), the original
+return address is removed from cur_ret_stack and is transiently moved
+arbitrarily by the compiler before being returned in rax. The return_to_handler
+trampoline moves this into rdi before jumping to it.
+
+Architectures might not always be able to unwind such sequences, such as when
+ftrace_return_to_handler() has removed the address from cur_ret_stack, and the
+location of the return address cannot be reliably determined.
+
+It is recommended that architectures unwind cases where return_to_handler has
+not yet been returned to, but architectures are not required to unwind from the
+middle of return_to_handler and can report this as unreliable. Architectures
+are not required to unwind from other trampolines which modify the return
+address.
+
+4.5 Obscuring of return addresses
+---------------------------------
+
+Some trampolines do not rewrite the return address in order to intercept
+returns, but do transiently clobber the return address or other unwind state.
+
+For example, the x86_64 implementation of optprobes patches the probed function
+with a JMP instruction which targets the associated optprobe trampoline. When
+the probe is hit, the CPU will branch to the optprobe trampoline, and the
+address of the probed function is not held in any register or on the stack.
+
+Similarly, the arm64 implementation of DYNAMIC_FTRACE_WITH_REGS patches traced
+functions with the following:
+
+.. code-block:: none
+
+   MOV X9, X30
+   BL <trampoline>
+
+The MOV saves the link register (X30) into X9 to preserve the return address
+before the BL clobbers the link register and branches to the trampoline. At the
+start of the trampoline, the address of the traced function is in X9 rather
+than the link register as would usually be the case.
+
+Architectures must either ensure that unwinders either reliably unwind
+such cases, or report the unwinding as unreliable.
+
+4.6 Link register unreliability
+-------------------------------
+
+On some other architectures, 'call' instructions place the return address into a
+link register, and 'return' instructions consume the return address from the
+link register without modifying the register. On these architectures software
+must save the return address to the stack prior to making a function call. Over
+the duration of a function call, the return address may be held in the link
+register alone, on the stack alone, or in both locations.
+
+Unwinders typically assume the link register is always live, but this
+assumption can lead to unreliable stack traces. For example, consider the
+following arm64 assembly for a simple function:
+
+.. code-block:: none
+
+   function:
+           STP X29, X30, [SP, -16]!
+           MOV X29, SP
+           BL <other_function>
+           LDP X29, X30, [SP], #16
+           RET
+
+At entry to the function, the link register (x30) points to the caller, and the
+frame pointer (X29) points to the caller's frame including the caller's return
+address. The first two instructions create a new stackframe and update the
+frame pointer, and at this point the link register and the frame pointer both
+describe this function's return address. A trace at this point may describe
+this function twice, and if the function return is being traced, the unwinder
+may consume two entries from the fgraph return stack rather than one entry.
+
+The BL invokes 'other_function' with the link register pointing to this
+function's LDR and the frame pointer pointing to this function's stackframe.
+When 'other_function' returns, the link register is left pointing at the BL,
+and so a trace at this point could result in 'function' appearing twice in the
+backtrace.
+
+Similarly, a function may deliberately clobber the LR, e.g.
+
+.. code-block:: none
+
+   caller:
+           STP X29, X30, [SP, -16]!
+           MOV X29, SP
+           ADR LR, <callee>
+           BLR LR
+           LDP X29, X30, [SP], #16
+           RET
+
+The ADR places the address of 'callee' into the LR, before the BLR branches to
+this address. If a trace is made immediately after the ADR, 'callee' will
+appear to be the parent of 'caller', rather than the child.
+
+Due to cases such as the above, it may only be possible to reliably consume a
+link register value at a function call boundary. Architectures where this is
+the case must reject unwinding across exception boundaries unless they can
+reliably identify when the LR or stack value should be used (e.g. using
+metadata generated by objtool).
diff --git a/Documentation/livepatch/shadow-vars.rst b/Documentation/livepatch/shadow-vars.rst
new file mode 100644
index 0000000000..7a7098bfb5
--- /dev/null
+++ b/Documentation/livepatch/shadow-vars.rst
@@ -0,0 +1,226 @@
+================
+Shadow Variables
+================
+
+Shadow variables are a simple way for livepatch modules to associate
+additional "shadow" data with existing data structures.  Shadow data is
+allocated separately from parent data structures, which are left
+unmodified.  The shadow variable API described in this document is used
+to allocate/add and remove/free shadow variables to/from their parents.
+
+The implementation introduces a global, in-kernel hashtable that
+associates pointers to parent objects and a numeric identifier of the
+shadow data.  The numeric identifier is a simple enumeration that may be
+used to describe shadow variable version, class or type, etc.  More
+specifically, the parent pointer serves as the hashtable key while the
+numeric id subsequently filters hashtable queries.  Multiple shadow
+variables may attach to the same parent object, but their numeric
+identifier distinguishes between them.
+
+
+1. Brief API summary
+====================
+
+(See the full API usage docbook notes in livepatch/shadow.c.)
+
+A hashtable references all shadow variables.  These references are
+stored and retrieved through a <obj, id> pair.
+
+* The klp_shadow variable data structure encapsulates both tracking
+  meta-data and shadow-data:
+
+  - meta-data
+
+    - obj - pointer to parent object
+    - id - data identifier
+
+  - data[] - storage for shadow data
+
+It is important to note that the klp_shadow_alloc() and
+klp_shadow_get_or_alloc() are zeroing the variable by default.
+They also allow to call a custom constructor function when a non-zero
+value is needed. Callers should provide whatever mutual exclusion
+is required.
+
+Note that the constructor is called under klp_shadow_lock spinlock. It allows
+to do actions that can be done only once when a new variable is allocated.
+
+* klp_shadow_get() - retrieve a shadow variable data pointer
+  - search hashtable for <obj, id> pair
+
+* klp_shadow_alloc() - allocate and add a new shadow variable
+  - search hashtable for <obj, id> pair
+
+  - if exists
+
+    - WARN and return NULL
+
+  - if <obj, id> doesn't already exist
+
+    - allocate a new shadow variable
+    - initialize the variable using a custom constructor and data when provided
+    - add <obj, id> to the global hashtable
+
+* klp_shadow_get_or_alloc() - get existing or alloc a new shadow variable
+  - search hashtable for <obj, id> pair
+
+  - if exists
+
+    - return existing shadow variable
+
+  - if <obj, id> doesn't already exist
+
+    - allocate a new shadow variable
+    - initialize the variable using a custom constructor and data when provided
+    - add <obj, id> pair to the global hashtable
+
+* klp_shadow_free() - detach and free a <obj, id> shadow variable
+  - find and remove a <obj, id> reference from global hashtable
+
+    - if found
+
+      - call destructor function if defined
+      - free shadow variable
+
+* klp_shadow_free_all() - detach and free all <_, id> shadow variables
+  - find and remove any <_, id> references from global hashtable
+
+    - if found
+
+      - call destructor function if defined
+      - free shadow variable
+
+
+2. Use cases
+============
+
+(See the example shadow variable livepatch modules in samples/livepatch/
+for full working demonstrations.)
+
+For the following use-case examples, consider commit 1d147bfa6429
+("mac80211: fix AP powersave TX vs.  wakeup race"), which added a
+spinlock to net/mac80211/sta_info.h :: struct sta_info.  Each use-case
+example can be considered a stand-alone livepatch implementation of this
+fix.
+
+
+Matching parent's lifecycle
+---------------------------
+
+If parent data structures are frequently created and destroyed, it may
+be easiest to align their shadow variables lifetimes to the same
+allocation and release functions.  In this case, the parent data
+structure is typically allocated, initialized, then registered in some
+manner.  Shadow variable allocation and setup can then be considered
+part of the parent's initialization and should be completed before the
+parent "goes live" (ie, any shadow variable get-API requests are made
+for this <obj, id> pair.)
+
+For commit 1d147bfa6429, when a parent sta_info structure is allocated,
+allocate a shadow copy of the ps_lock pointer, then initialize it::
+
+  #define PS_LOCK 1
+  struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
+				  const u8 *addr, gfp_t gfp)
+  {
+	struct sta_info *sta;
+	spinlock_t *ps_lock;
+
+	/* Parent structure is created */
+	sta = kzalloc(sizeof(*sta) + hw->sta_data_size, gfp);
+
+	/* Attach a corresponding shadow variable, then initialize it */
+	ps_lock = klp_shadow_alloc(sta, PS_LOCK, sizeof(*ps_lock), gfp,
+				   NULL, NULL);
+	if (!ps_lock)
+		goto shadow_fail;
+	spin_lock_init(ps_lock);
+	...
+
+When requiring a ps_lock, query the shadow variable API to retrieve one
+for a specific struct sta_info:::
+
+  void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
+  {
+	spinlock_t *ps_lock;
+
+	/* sync with ieee80211_tx_h_unicast_ps_buf */
+	ps_lock = klp_shadow_get(sta, PS_LOCK);
+	if (ps_lock)
+		spin_lock(ps_lock);
+	...
+
+When the parent sta_info structure is freed, first free the shadow
+variable::
+
+  void sta_info_free(struct ieee80211_local *local, struct sta_info *sta)
+  {
+	klp_shadow_free(sta, PS_LOCK, NULL);
+	kfree(sta);
+	...
+
+
+In-flight parent objects
+------------------------
+
+Sometimes it may not be convenient or possible to allocate shadow
+variables alongside their parent objects.  Or a livepatch fix may
+require shadow variables for only a subset of parent object instances.
+In these cases, the klp_shadow_get_or_alloc() call can be used to attach
+shadow variables to parents already in-flight.
+
+For commit 1d147bfa6429, a good spot to allocate a shadow spinlock is
+inside ieee80211_sta_ps_deliver_wakeup()::
+
+  int ps_lock_shadow_ctor(void *obj, void *shadow_data, void *ctor_data)
+  {
+	spinlock_t *lock = shadow_data;
+
+	spin_lock_init(lock);
+	return 0;
+  }
+
+  #define PS_LOCK 1
+  void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
+  {
+	spinlock_t *ps_lock;
+
+	/* sync with ieee80211_tx_h_unicast_ps_buf */
+	ps_lock = klp_shadow_get_or_alloc(sta, PS_LOCK,
+			sizeof(*ps_lock), GFP_ATOMIC,
+			ps_lock_shadow_ctor, NULL);
+
+	if (ps_lock)
+		spin_lock(ps_lock);
+	...
+
+This usage will create a shadow variable, only if needed, otherwise it
+will use one that was already created for this <obj, id> pair.
+
+Like the previous use-case, the shadow spinlock needs to be cleaned up.
+A shadow variable can be freed just before its parent object is freed,
+or even when the shadow variable itself is no longer required.
+
+
+Other use-cases
+---------------
+
+Shadow variables can also be used as a flag indicating that a data
+structure was allocated by new, livepatched code.  In this case, it
+doesn't matter what data value the shadow variable holds, its existence
+suggests how to handle the parent object.
+
+
+3. References
+=============
+
+* https://github.com/dynup/kpatch
+
+  The livepatch implementation is based on the kpatch version of shadow
+  variables.
+
+* http://files.mkgnu.net/files/dynamos/doc/papers/dynamos_eurosys_07.pdf
+
+  Dynamic and Adaptive Updates of Non-Quiescent Subsystems in Commodity
+  Operating System Kernels (Kritis Makris, Kyung Dong Ryu 2007) presented
+  a datatype update technique called "shadow data structures".
diff --git a/Documentation/livepatch/system-state.rst b/Documentation/livepatch/system-state.rst
new file mode 100644
index 0000000000..7a3935fd81
--- /dev/null
+++ b/Documentation/livepatch/system-state.rst
@@ -0,0 +1,167 @@
+====================
+System State Changes
+====================
+
+Some users are really reluctant to reboot a system. This brings the need
+to provide more livepatches and maintain some compatibility between them.
+
+Maintaining more livepatches is much easier with cumulative livepatches.
+Each new livepatch completely replaces any older one. It can keep,
+add, and even remove fixes. And it is typically safe to replace any version
+of the livepatch with any other one thanks to the atomic replace feature.
+
+The problems might come with shadow variables and callbacks. They might
+change the system behavior or state so that it is no longer safe to
+go back and use an older livepatch or the original kernel code. Also
+any new livepatch must be able to detect what changes have already been
+done by the already installed livepatches.
+
+This is where the livepatch system state tracking gets useful. It
+allows to:
+
+  - store data needed to manipulate and restore the system state
+
+  - define compatibility between livepatches using a change id
+    and version
+
+
+1. Livepatch system state API
+=============================
+
+The state of the system might get modified either by several livepatch callbacks
+or by the newly used code. Also it must be possible to find changes done by
+already installed livepatches.
+
+Each modified state is described by struct klp_state, see
+include/linux/livepatch.h.
+
+Each livepatch defines an array of struct klp_states. They mention
+all states that the livepatch modifies.
+
+The livepatch author must define the following two fields for each
+struct klp_state:
+
+  - *id*
+
+    - Non-zero number used to identify the affected system state.
+
+  - *version*
+
+    - Number describing the variant of the system state change that
+      is supported by the given livepatch.
+
+The state can be manipulated using two functions:
+
+  - klp_get_state()
+
+    - Get struct klp_state associated with the given livepatch
+      and state id.
+
+  - klp_get_prev_state()
+
+    - Get struct klp_state associated with the given feature id and
+      already installed livepatches.
+
+2. Livepatch compatibility
+==========================
+
+The system state version is used to prevent loading incompatible livepatches.
+The check is done when the livepatch is enabled. The rules are:
+
+  - Any completely new system state modification is allowed.
+
+  - System state modifications with the same or higher version are allowed
+    for already modified system states.
+
+  - Cumulative livepatches must handle all system state modifications from
+    already installed livepatches.
+
+  - Non-cumulative livepatches are allowed to touch already modified
+    system states.
+
+3. Supported scenarios
+======================
+
+Livepatches have their life-cycle and the same is true for the system
+state changes. Every compatible livepatch has to support the following
+scenarios:
+
+  - Modify the system state when the livepatch gets enabled and the state
+    has not been already modified by a livepatches that are being
+    replaced.
+
+  - Take over or update the system state modification when is has already
+    been done by a livepatch that is being replaced.
+
+  - Restore the original state when the livepatch is disabled.
+
+  - Restore the previous state when the transition is reverted.
+    It might be the original system state or the state modification
+    done by livepatches that were being replaced.
+
+  - Remove any already made changes when error occurs and the livepatch
+    cannot get enabled.
+
+4. Expected usage
+=================
+
+System states are usually modified by livepatch callbacks. The expected
+role of each callback is as follows:
+
+*pre_patch()*
+
+  - Allocate *state->data* when necessary. The allocation might fail
+    and *pre_patch()* is the only callback that could stop loading
+    of the livepatch. The allocation is not needed when the data
+    are already provided by previously installed livepatches.
+
+  - Do any other preparatory action that is needed by
+    the new code even before the transition gets finished.
+    For example, initialize *state->data*.
+
+    The system state itself is typically modified in *post_patch()*
+    when the entire system is able to handle it.
+
+  - Clean up its own mess in case of error. It might be done by a custom
+    code or by calling *post_unpatch()* explicitly.
+
+*post_patch()*
+
+  - Copy *state->data* from the previous livepatch when they are
+    compatible.
+
+  - Do the actual system state modification. Eventually allow
+    the new code to use it.
+
+  - Make sure that *state->data* has all necessary information.
+
+  - Free *state->data* from replaces livepatches when they are
+    not longer needed.
+
+*pre_unpatch()*
+
+  - Prevent the code, added by the livepatch, relying on the system
+    state change.
+
+  - Revert the system state modification..
+
+*post_unpatch()*
+
+  - Distinguish transition reverse and livepatch disabling by
+    checking *klp_get_prev_state()*.
+
+  - In case of transition reverse, restore the previous system
+    state. It might mean doing nothing.
+
+  - Remove any not longer needed setting or data.
+
+.. note::
+
+   *pre_unpatch()* typically does symmetric operations to *post_patch()*.
+   Except that it is called only when the livepatch is being disabled.
+   Therefore it does not need to care about any previously installed
+   livepatch.
+
+   *post_unpatch()* typically does symmetric operations to *pre_patch()*.
+   It might be called also during the transition reverse. Therefore it
+   has to handle the state of the previously installed livepatches.