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

Pull livepatching updates from Jiri Kosina:

 - remove of our own implementation of architecture-specific relocation
   code and leveraging existing code in the module loader to perform
   arch-dependent work, from Jessica Yu.

   The relevant patches have been acked by Rusty (for module.c) and
   Heiko (for s390).

 - live patching support for ppc64le, which is a joint work of Michael
   Ellerman and Torsten Duwe.  This is coming from topic branch that is
   share between livepatching.git and ppc tree.

 - addition of livepatching documentation from Petr Mladek

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: make object/func-walking helpers more robust
  livepatch: Add some basic livepatch documentation
  powerpc/livepatch: Add live patching support on ppc64le
  powerpc/livepatch: Add livepatch stack to struct thread_info
  powerpc/livepatch: Add livepatch header
  livepatch: Allow architectures to specify an alternate ftrace location
  ftrace: Make ftrace_location_range() global
  livepatch: robustify klp_register_patch() API error checking
  Documentation: livepatch: outline Elf format and requirements for patch modules
  livepatch: reuse module loader code to write relocations
  module: s390: keep mod_arch_specific for livepatch modules
  module: preserve Elf information for livepatch modules
  Elf: add livepatch-specific Elf constants

Documentation/livepatch/livepatch.txt

+=========
+Livepatch
+=========
+
+This document outlines basic information about kernel livepatching.
+
+Table of Contents:
+
+1. Motivation
+2. Kprobes, Ftrace, Livepatching
+3. Consistency model
+4. Livepatch module
+   4.1. New functions
+   4.2. Metadata
+   4.3. Livepatch module handling
+5. Livepatch life-cycle
+   5.1. Registration
+   5.2. Enabling
+   5.3. Disabling
+   5.4. Unregistration
+6. Sysfs
+7. Limitations
+
+
+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. The theory is not yet finished. See the discussion at
+http://thread.gmane.org/gmane.linux.kernel/1823033/focus=1828189
+
+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.
+
+
+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.txt 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. 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.
+
+
+4.3. Livepatch module handling
+------------------------------
+
+The usual behavior is that the new functions will get used when
+the livepatch module is loaded. For this, the module init() function
+has to register the patch (struct klp_patch) and enable it. See the
+section "Livepatch life-cycle" below for more details about these
+two operations.
+
+Module removal is only safe when there are no users of the underlying
+functions.  The immediate consistency model is not able to detect this;
+therefore livepatch modules cannot be removed. See "Limitations" below.
+
+5. Livepatch life-cycle
+=======================
+
+Livepatching defines four basic operations that define the life cycle of each
+live patch: registration, enabling, disabling and unregistration.  There are
+several reasons why it is done this way.
+
+First, the patch is applied only when all patched symbols for already
+loaded objects are found. The error handling is much easier if this
+check is done before particular functions get redirected.
+
+Second, the immediate consistency model does not guarantee that anyone is not
+sleeping in the new code after the patch is reverted. This means that the new
+code needs to stay around "forever". If the code is there, one could apply it
+again. Therefore it makes sense to separate the operations that might be done
+once and those that need to be repeated when the patch is enabled (applied)
+again.
+
+Third, it might take some time until the entire system is migrated
+when a more complex consistency model is used. The patch revert might
+block the livepatch module removal for too long. Therefore it is useful
+to revert the patch using a separate operation that might be called
+explicitly. But it does not make sense to remove all information
+until the livepatch module is really removed.
+
+
+5.1. Registration
+-----------------
+
+Each patch first has to be registered using klp_register_patch(). This makes
+the patch known to the livepatch framework. Also it does some preliminary
+computing and checks.
+
+In particular, the patch is added into the list of known patches. 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 operation
+fails.
+
+
+5.2. Enabling
+-------------
+
+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.
+
+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
+list (see field `func_stack`) of the struct klp_ops. The last added
+entry is chosen by the ftrace handler and becomes the active function
+replacement.
+
+Note that the patches might be enabled in a different order than they were
+registered.
+
+
+5.3. Disabling
+--------------
+
+Enabled patches might get disabled either by calling klp_disable_patch() or
+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.
+
+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
+becomes empty.
+
+Patches must be disabled in exactly the reverse order in which they were
+enabled. It makes the problem and the implementation much easier.
+
+
+5.4. Unregistration
+-------------------
+
+Disabled patches might be unregistered by calling klp_unregister_patch().
+This can be done only when the patch is disabled and the code is no longer
+used. It must be called before the livepatch module gets unloaded.
+
+At this stage, all the relevant sys-fs entries are removed and the patch
+is removed from the list of known patches.
+
+
+6. Sysfs
+========
+
+Information about the registered patches can be found under
+/sys/kernel/livepatch. The patches could be enabled and disabled
+by writing there.
+
+See Documentation/ABI/testing/sysfs-kernel-livepatch for more details.
+
+
+7. Limitations
+==============
+
+The current Livepatch implementation has several limitations:
+
+
+  + The patch must not change the semantic of the patched functions.
+
+    The current implementation guarantees only that either the old
+    or the new function is called. The functions are patched one
+    by one. It means that the patch must _not_ change the semantic
+    of the function.
+
+
+  + Data structures can not be patched.
+
+    There is no support to version data structures or anyhow migrate
+    one structure into another. Also the simple consistency model does
+    not allow to switch more functions atomically.
+
+    Once there is more complex consistency mode, it will be possible to
+    use some workarounds. For example, it will be possible to use a hole
+    for a new member because the data structure is aligned. Or it will
+    be possible to use an existing member for something else.
+
+    There are no plans to add more generic support for modified structures
+    at the moment.
+
+
+  + 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".
+
+
+  + Anything inlined into __schedule() can not be patched.
+
+    The switch_to macro is inlined into __schedule(). It switches the
+    context between two processes in the middle of the macro. It does
+    not save RIP in x86_64 version (contrary to 32-bit version). Instead,
+    the currently used __schedule()/switch_to() handles both processes.
+
+    Now, let's have two different tasks. One calls the original
+    __schedule(), its registers are stored in a defined order and it
+    goes to sleep in the switch_to macro and some other task is restored
+    using the original __schedule(). Then there is the second task which
+    calls patched__schedule(), it goes to sleep there and the first task
+    is picked by the patched__schedule(). Its RSP is restored and now
+    the registers should be restored as well. But the order is different
+    in the new patched__schedule(), so...
+
+    There is work in progress to remove this limitation.
+
+
+  + Livepatch modules can not be removed.
+
+    The current implementation just redirects the functions at the very
+    beginning. It does not check if the functions are in use. In other
+    words, it knows when the functions get called but it does not
+    know when the functions return. Therefore it can not decide when
+    the livepatch module can be safely removed.
+
+    This will get most likely solved once a more complex consistency model
+    is supported. The idea is that a safe state for patching should also
+    mean a safe state for removing the patch.
+
+    Note that the patch itself might get disabled by writing zero
+    to /sys/kernel/livepatch/<patch>/enabled. It causes that the new
+    code will not longer get called. But it does not guarantee
+    that anyone is not sleeping anywhere in the new code.
+
+
+  + 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 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.

Documentation/livepatch/module-elf-format.txt

+===========================
+Livepatch module Elf format
+===========================
+
+This document outlines the Elf format requirements that livepatch modules must follow.
+
+-----------------
+Table of Contents
+-----------------
+0. Background and motivation
+1. Livepatch modinfo field
+2. Livepatch relocation sections
+   2.1 What are livepatch relocation sections?
+   2.2 Livepatch relocation section format
+       2.2.1 Required flags
+       2.2.2 Required name format
+       2.2.3 Example livepatch relocation section names
+       2.2.4 Example `readelf --sections` output
+       2.2.5 Example `readelf --relocs` output
+3. Livepatch symbols
+   3.1 What are livepatch symbols?
+   3.2 A livepatch module's symbol table
+   3.3 Livepatch symbol format
+       3.3.1 Required flags
+       3.3.2 Required name format
+       3.3.3 Example livepatch symbol names
+       3.3.4 Example `readelf --symbols` output
+4. Symbol table and Elf section access
+
+----------------------------
+0. 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 4). 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.
+
+0.1 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().
+
+================================
+PATCH MODULE FORMAT REQUIREMENTS
+================================
+
+--------------------------
+1. 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
+
+--------------------------------
+2. Livepatch relocation sections
+--------------------------------
+
+-------------------------------------------
+2.1 What are 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 4), 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.
+
+---------------------------------------
+2.2 Livepatch relocation section format
+---------------------------------------
+
+2.2.1 Required flags
+--------------------
+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).
+
+2.2.2 Required name format
+--------------------------
+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.
+
+2.2.3 Example livepatch relocation section names:
+-------------------------------------------------
+.klp.rela.ext4.text.ext4_attr_store
+.klp.rela.vmlinux.text.cmdline_proc_show
+
+2.2.4 Example `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).
+
+2.2.5 Example `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.
+
+--------------------
+3. Livepatch symbols
+--------------------
+
+-------------------------------
+3.1 What are 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.
+
+-------------------------------------
+3.2 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.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 ]
+
+---------------------------
+3.3 Livepatch symbol format
+---------------------------
+
+3.3.1 Required flags
+--------------------
+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.
+
+3.3.2 Required name format
+--------------------------
+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.
+
+3.3.3 Example livepatch symbol names:
+-------------------------------------
+.klp.sym.vmlinux.snprintf,0
+.klp.sym.vmlinux.printk,0
+.klp.sym.btrfs.btrfs_ktype,0
+
+3.3.4 Example `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.
+
+--------------------------------------
+4. 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 klp_modinfo struct. When a livepatch module loads,
+this struct is filled in by the module loader. Its fields are documented below:
+
+struct klp_modinfo {
+	Elf_Ehdr hdr; /* Elf header */
+	Elf_Shdr *sechdrs; /* Section header table */
+	char *secstrings; /* String table for the section headers */
+	unsigned int symndx; /* The symbol table section index */
+};

MAINTAINERS

@@ -6699,6 +6699,7 @@ F:	kernel/livepatch/
 F:	include/linux/livepatch.h
 F:	arch/x86/include/asm/livepatch.h
 F:	arch/x86/kernel/livepatch.c
+F:	Documentation/livepatch/
 F:	Documentation/ABI/testing/sysfs-kernel-livepatch
 F:	samples/livepatch/
 L:	live-patching@vger.kernel.org

arch/powerpc/Kconfig

@@ -160,6 +160,7 @@ config PPC
 	select HAVE_ARCH_SECCOMP_FILTER
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
+	select HAVE_LIVEPATCH if HAVE_DYNAMIC_FTRACE_WITH_REGS
 
 config GENERIC_CSUM
 	def_bool CPU_LITTLE_ENDIAN
@@ -1107,3 +1108,5 @@ config PPC_LIB_RHEAP
 	bool
 
 source "arch/powerpc/kvm/Kconfig"
+
+source "kernel/livepatch/Kconfig"

arch/x86/kernel/livepatch.c → arch/powerpc/include/asm/livepatch.h

 /*
- * livepatch.c - x86-specific Kernel Live Patching Core
+ * livepatch.h - powerpc-specific Kernel Live Patching Core
  *
- * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
- * Copyright (C) 2014 SUSE
+ * Copyright (C) 2015-2016, SUSE, IBM Corp.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -17,54 +16,47 @@
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
+#ifndef _ASM_POWERPC_LIVEPATCH_H
+#define _ASM_POWERPC_LIVEPATCH_H
 
 #include <linux/module.h>
-#include <linux/uaccess.h>
-#include <asm/elf.h>
-#include <asm/livepatch.h>
+#include <linux/ftrace.h>
 
-/**
- * klp_write_module_reloc() - write a relocation in a module
- * @mod:	module in which the section to be modified is found
- * @type:	ELF relocation type (see asm/elf.h)
- * @loc:	address that the relocation should be written to
- * @value:	relocation value (sym address + addend)
- *
- * This function writes a relocation to the specified location for
- * a particular module.
- */
-int klp_write_module_reloc(struct module *mod, unsigned long type,
-			   unsigned long loc, unsigned long value)
+#ifdef CONFIG_LIVEPATCH
+static inline int klp_check_compiler_support(void)
+{
+	return 0;
+}
+
+static inline int klp_write_module_reloc(struct module *mod, unsigned long
+		type, unsigned long loc, unsigned long value)
 {
-	size_t size = 4;
-	unsigned long val;
-	unsigned long core = (unsigned long)mod->core_layout.base;
-	unsigned long core_size = mod->core_layout.size;
+	/* This requires infrastructure changes; we need the loadinfos. */
+	return -ENOSYS;
+}
 
-	switch (type) {
-	case R_X86_64_NONE:
-		return 0;
-	case R_X86_64_64:
-		val = value;
-		size = 8;
-		break;
-	case R_X86_64_32:
-		val = (u32)value;
-		break;
-	case R_X86_64_32S:
-		val = (s32)value;
-		break;
-	case R_X86_64_PC32:
-		val = (u32)(value - loc);
-		break;
-	default:
-		/* unsupported relocation type */
-		return -EINVAL;
-	}
+static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+{
+	regs->nip = ip;
+}
 
-	if (loc < core || loc >= core + core_size)
-		/* loc does not point to any symbol inside the module */
-		return -EINVAL;
+#define klp_get_ftrace_location klp_get_ftrace_location
+static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
+{
+	/*
+	 * Live patch works only with -mprofile-kernel on PPC. In this case,
+	 * the ftrace location is always within the first 16 bytes.
+	 */
+	return ftrace_location_range(faddr, faddr + 16);
+}
 
-	return probe_kernel_write((void *)loc, &val, size);
+static inline void klp_init_thread_info(struct thread_info *ti)
+{
+	/* + 1 to account for STACK_END_MAGIC */
+	ti->livepatch_sp = (unsigned long *)(ti + 1) + 1;
 }
+#else
+static void klp_init_thread_info(struct thread_info *ti) { }
+#endif /* CONFIG_LIVEPATCH */
+
+#endif /* _ASM_POWERPC_LIVEPATCH_H */

arch/powerpc/include/asm/thread_info.h

@@ -43,7 +43,9 @@ struct thread_info {
 	int		preempt_count;		/* 0 => preemptable,
 						   <0 => BUG */
 	unsigned long	local_flags;		/* private flags for thread */
-
+#ifdef CONFIG_LIVEPATCH
+	unsigned long *livepatch_sp;
+#endif
 	/* low level flags - has atomic operations done on it */
 	unsigned long	flags ____cacheline_aligned_in_smp;
 };

arch/powerpc/kernel/asm-offsets.c

@@ -86,6 +86,10 @@ int main(void)
 	DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit));
 #endif /* CONFIG_PPC64 */
 
+#ifdef CONFIG_LIVEPATCH
+	DEFINE(TI_livepatch_sp, offsetof(struct thread_info, livepatch_sp));
+#endif
+
 	DEFINE(KSP, offsetof(struct thread_struct, ksp));
 	DEFINE(PT_REGS, offsetof(struct thread_struct, regs));
 #ifdef CONFIG_BOOKE

arch/powerpc/kernel/entry_64.S

@@ -20,6 +20,7 @@
 
 #include <linux/errno.h>
 #include <linux/err.h>
+#include <linux/magic.h>
 #include <asm/unistd.h>
 #include <asm/processor.h>
 #include <asm/page.h>
@@ -1248,6 +1249,9 @@ _GLOBAL(ftrace_caller)
 	addi	r3,r3,function_trace_op@toc@l
 	ld	r5,0(r3)
 
+#ifdef CONFIG_LIVEPATCH
+	mr	r14,r7		/* remember old NIP */
+#endif
 	/* Calculate ip from nip-4 into r3 for call below */
 	subi    r3, r7, MCOUNT_INSN_SIZE
 
@@ -1272,6 +1276,9 @@ ftrace_call:
 	/* Load ctr with the possibly modified NIP */
 	ld	r3, _NIP(r1)
 	mtctr	r3
+#ifdef CONFIG_LIVEPATCH
+	cmpd	r14,r3		/* has NIP been altered? */
+#endif
 
 	/* Restore gprs */
 	REST_8GPRS(0,r1)
@@ -1289,6 +1296,11 @@ ftrace_call:
 	ld	r0, LRSAVE(r1)
 	mtlr	r0
 
+#ifdef CONFIG_LIVEPATCH
+        /* Based on the cmpd above, if the NIP was altered handle livepatch */
+	bne-	livepatch_handler
+#endif
+
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	stdu	r1, -112(r1)
 .globl ftrace_graph_call
@@ -1305,6 +1317,91 @@ _GLOBAL(ftrace_graph_stub)
 
 _GLOBAL(ftrace_stub)
 	blr
+
+#ifdef CONFIG_LIVEPATCH
+	/*
+	 * This function runs in the mcount context, between two functions. As
+	 * such it can only clobber registers which are volatile and used in
+	 * function linkage.
+	 *
+	 * We get here when a function A, calls another function B, but B has
+	 * been live patched with a new function C.
+	 *
+	 * On entry:
+	 *  - we have no stack frame and can not allocate one
+	 *  - LR points back to the original caller (in A)
+	 *  - CTR holds the new NIP in C
+	 *  - r0 & r12 are free
+	 *
+	 * r0 can't be used as the base register for a DS-form load or store, so
+	 * we temporarily shuffle r1 (stack pointer) into r0 and then put it back.
+	 */
+livepatch_handler:
+	CURRENT_THREAD_INFO(r12, r1)
+
+	/* Save stack pointer into r0 */
+	mr	r0, r1
+
+	/* Allocate 3 x 8 bytes */
+	ld	r1, TI_livepatch_sp(r12)
+	addi	r1, r1, 24
+	std	r1, TI_livepatch_sp(r12)
+
+	/* Save toc & real LR on livepatch stack */
+	std	r2,  -24(r1)
+	mflr	r12
+	std	r12, -16(r1)
+
+	/* Store stack end marker */
+	lis     r12, STACK_END_MAGIC@h
+	ori     r12, r12, STACK_END_MAGIC@l
+	std	r12, -8(r1)
+
+	/* Restore real stack pointer */
+	mr	r1, r0
+
+	/* Put ctr in r12 for global entry and branch there */
+	mfctr	r12
+	bctrl
+
+	/*
+	 * Now we are returning from the patched function to the original
+	 * caller A. We are free to use r0 and r12, and we can use r2 until we
+	 * restore it.
+	 */
+
+	CURRENT_THREAD_INFO(r12, r1)
+
+	/* Save stack pointer into r0 */
+	mr	r0, r1
+
+	ld	r1, TI_livepatch_sp(r12)
+
+	/* Check stack marker hasn't been trashed */
+	lis     r2,  STACK_END_MAGIC@h
+	ori     r2,  r2, STACK_END_MAGIC@l
+	ld	r12, -8(r1)
+1:	tdne	r12, r2
+	EMIT_BUG_ENTRY 1b, __FILE__, __LINE__ - 1, 0
+
+	/* Restore LR & toc from livepatch stack */
+	ld	r12, -16(r1)
+	mtlr	r12
+	ld	r2,  -24(r1)
+
+	/* Pop livepatch stack frame */
+	CURRENT_THREAD_INFO(r12, r0)
+	subi	r1, r1, 24
+	std	r1, TI_livepatch_sp(r12)
+
+	/* Restore real stack pointer */
+	mr	r1, r0
+
+	/* Return to original caller of live patched function */
+	blr
+#endif
+
+
 #else
 _GLOBAL_TOC(_mcount)
 	/* Taken from output of objdump from lib64/glibc */

arch/powerpc/kernel/irq.c

@@ -66,6 +66,7 @@
 #include <asm/udbg.h>
 #include <asm/smp.h>
 #include <asm/debug.h>
+#include <asm/livepatch.h>
 
 #ifdef CONFIG_PPC64
 #include <asm/paca.h>
@@ -607,10 +608,12 @@ void irq_ctx_init(void)
 		memset((void *)softirq_ctx[i], 0, THREAD_SIZE);
 		tp = softirq_ctx[i];
 		tp->cpu = i;
+		klp_init_thread_info(tp);
 
 		memset((void *)hardirq_ctx[i], 0, THREAD_SIZE);
 		tp = hardirq_ctx[i];
 		tp->cpu = i;
+		klp_init_thread_info(tp);
 	}
 }
 

arch/powerpc/kernel/process.c

@@ -55,6 +55,8 @@
 #include <asm/firmware.h>
 #endif
 #include <asm/code-patching.h>
+#include <asm/livepatch.h>
+
 #include <linux/kprobes.h>
 #include <linux/kdebug.h>
 
@@ -1400,13 +1402,15 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 	extern void ret_from_kernel_thread(void);
 	void (*f)(void);
 	unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
+	struct thread_info *ti = task_thread_info(p);
+
+	klp_init_thread_info(ti);
 
 	/* Copy registers */
 	sp -= sizeof(struct pt_regs);
 	childregs = (struct pt_regs *) sp;
 	if (unlikely(p->flags & PF_KTHREAD)) {
 		/* kernel thread */
-		struct thread_info *ti = (void *)task_stack_page(p);
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->gpr[1] = sp + sizeof(struct pt_regs);
 		/* function */

arch/powerpc/kernel/setup_64.c

@@ -69,6 +69,7 @@
 #include <asm/kvm_ppc.h>
 #include <asm/hugetlb.h>
 #include <asm/epapr_hcalls.h>
+#include <asm/livepatch.h>
 
 #ifdef DEBUG
 #define DBG(fmt...) udbg_printf(fmt)
@@ -667,16 +668,16 @@ static void __init emergency_stack_init(void)
 	limit = min(safe_stack_limit(), ppc64_rma_size);
 
 	for_each_possible_cpu(i) {
-		unsigned long sp;
-		sp  = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
-		sp += THREAD_SIZE;
-		paca[i].emergency_sp = __va(sp);
+		struct thread_info *ti;
+		ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
+		klp_init_thread_info(ti);
+		paca[i].emergency_sp = (void *)ti + THREAD_SIZE;
 
 #ifdef CONFIG_PPC_BOOK3S_64
 		/* emergency stack for machine check exception handling. */
-		sp  = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
-		sp += THREAD_SIZE;
-		paca[i].mc_emergency_sp = __va(sp);
+		ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
+		klp_init_thread_info(ti);
+		paca[i].mc_emergency_sp = (void *)ti + THREAD_SIZE;
 #endif
 	}
 }
@@ -700,6 +701,8 @@ void __init setup_arch(char **cmdline_p)
 	if (ppc_md.panic)
 		setup_panic();
 
+	klp_init_thread_info(&init_thread_info);
+
 	init_mm.start_code = (unsigned long)_stext;
 	init_mm.end_code = (unsigned long) _etext;
 	init_mm.end_data = (unsigned long) _edata;

arch/s390/include/asm/livepatch.h

@@ -24,13 +24,6 @@ static inline int klp_check_compiler_support(void)
 	return 0;
 }
 
-static inline int klp_write_module_reloc(struct module *mod, unsigned long
-		type, unsigned long loc, unsigned long value)
-{
-	/* not supported yet */
-	return -ENOSYS;
-}
-
 static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 {
 	regs->psw.addr = ip;

arch/s390/kernel/module.c

@@ -51,6 +51,10 @@ void *module_alloc(unsigned long size)
 
 void module_arch_freeing_init(struct module *mod)
 {
+	if (is_livepatch_module(mod) &&
+	    mod->state == MODULE_STATE_LIVE)
+		return;
+
 	vfree(mod->arch.syminfo);
 	mod->arch.syminfo = NULL;
 }
@@ -425,7 +429,5 @@ int module_finalize(const Elf_Ehdr *hdr,
 		    struct module *me)
 {
 	jump_label_apply_nops(me);
-	vfree(me->arch.syminfo);
-	me->arch.syminfo = NULL;
 	return 0;
 }

arch/x86/include/asm/livepatch.h

@@ -32,8 +32,6 @@ static inline int klp_check_compiler_support(void)
 #endif
 	return 0;
 }
-int klp_write_module_reloc(struct module *mod, unsigned long type,
-			   unsigned long loc, unsigned long value);
 
 static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 {

arch/x86/kernel/Makefile

@@ -83,7 +83,6 @@ obj-$(CONFIG_X86_MPPARSE)	+= mpparse.o
 obj-y				+= apic/
 obj-$(CONFIG_X86_REBOOTFIXUPS)	+= reboot_fixups_32.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o
-obj-$(CONFIG_LIVEPATCH)		+= livepatch.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
 obj-$(CONFIG_X86_TSC)		+= trace_clock.o

include/linux/ftrace.h

@@ -455,6 +455,7 @@ int ftrace_update_record(struct dyn_ftrace *rec, int enable);
 int ftrace_test_record(struct dyn_ftrace *rec, int enable);
 void ftrace_run_stop_machine(int command);
 unsigned long ftrace_location(unsigned long ip);
+unsigned long ftrace_location_range(unsigned long start, unsigned long end);
 unsigned long ftrace_get_addr_new(struct dyn_ftrace *rec);
 unsigned long ftrace_get_addr_curr(struct dyn_ftrace *rec);
 

include/linux/livepatch.h

@@ -64,28 +64,9 @@ struct klp_func {
 	struct list_head stack_node;
 };
 
-/**
- * struct klp_reloc - relocation structure for live patching
- * @loc:	address where the relocation will be written
- * @sympos:	position in kallsyms to disambiguate symbols (optional)
- * @type:	ELF relocation type
- * @name:	name of the referenced symbol (for lookup/verification)
- * @addend:	offset from the referenced symbol
- * @external:	symbol is either exported or within the live patch module itself
- */
-struct klp_reloc {
-	unsigned long loc;
-	unsigned long sympos;
-	unsigned long type;
-	const char *name;
-	int addend;
-	int external;
-};
-
 /**
  * struct klp_object - kernel object structure for live patching
  * @name:	module name (or NULL for vmlinux)
- * @relocs:	relocation entries to be applied at load time
  * @funcs:	function entries for functions to be patched in the object
  * @kobj:	kobject for sysfs resources
  * @mod:	kernel module associated with the patched object
@@ -95,7 +76,6 @@ struct klp_reloc {
 struct klp_object {
 	/* external */
 	const char *name;
-	struct klp_reloc *relocs;
 	struct klp_func *funcs;
 
 	/* internal */
@@ -124,10 +104,12 @@ struct klp_patch {
 };
 
 #define klp_for_each_object(patch, obj) \
-	for (obj = patch->objs; obj->funcs; obj++)
+	for (obj = patch->objs; obj->funcs || obj->name; obj++)
 
 #define klp_for_each_func(obj, func) \
-	for (func = obj->funcs; func->old_name; func++)
+	for (func = obj->funcs; \
+	     func->old_name || func->new_func || func->old_sympos; \
+	     func++)
 
 int klp_register_patch(struct klp_patch *);
 int klp_unregister_patch(struct klp_patch *);

include/linux/module.h

@@ -330,6 +330,15 @@ struct mod_kallsyms {
 	char *strtab;
 };
 
+#ifdef CONFIG_LIVEPATCH
+struct klp_modinfo {
+	Elf_Ehdr hdr;
+	Elf_Shdr *sechdrs;
+	char *secstrings;
+	unsigned int symndx;
+};
+#endif
+
 struct module {
 	enum module_state state;
 
@@ -456,7 +465,11 @@ struct module {
 #endif
 
 #ifdef CONFIG_LIVEPATCH
+	bool klp; /* Is this a livepatch module? */
 	bool klp_alive;
+
+	/* Elf information */
+	struct klp_modinfo *klp_info;
 #endif
 
 #ifdef CONFIG_MODULE_UNLOAD
@@ -630,6 +643,18 @@ static inline bool module_requested_async_probing(struct module *module)
 	return module && module->async_probe_requested;
 }
 
+#ifdef CONFIG_LIVEPATCH
+static inline bool is_livepatch_module(struct module *mod)
+{
+	return mod->klp;
+}
+#else /* !CONFIG_LIVEPATCH */
+static inline bool is_livepatch_module(struct module *mod)
+{
+	return false;
+}
+#endif /* CONFIG_LIVEPATCH */
+
 #else /* !CONFIG_MODULES... */
 
 /* Given an address, look for it in the exception tables. */

include/uapi/linux/elf.h

@@ -282,16 +282,18 @@ typedef struct elf64_phdr {
 #define SHT_HIUSER	0xffffffff
 
 /* sh_flags */
-#define SHF_WRITE	0x1
-#define SHF_ALLOC	0x2
-#define SHF_EXECINSTR	0x4
-#define SHF_MASKPROC	0xf0000000
+#define SHF_WRITE		0x1
+#define SHF_ALLOC		0x2
+#define SHF_EXECINSTR		0x4
+#define SHF_RELA_LIVEPATCH	0x00100000
+#define SHF_MASKPROC		0xf0000000
 
 /* special section indexes */
 #define SHN_UNDEF	0
 #define SHN_LORESERVE	0xff00
 #define SHN_LOPROC	0xff00
 #define SHN_HIPROC	0xff1f
+#define SHN_LIVEPATCH	0xff20
 #define SHN_ABS		0xfff1
 #define SHN_COMMON	0xfff2
 #define SHN_HIRESERVE	0xffff

kernel/livepatch/core.c

@@ -28,6 +28,8 @@
 #include <linux/list.h>
 #include <linux/kallsyms.h>
 #include <linux/livepatch.h>
+#include <linux/elf.h>
+#include <linux/moduleloader.h>
 #include <asm/cacheflush.h>
 
 /**
@@ -204,75 +206,109 @@ static int klp_find_object_symbol(const char *objname, const char *name,
 	return -EINVAL;
 }
 
-/*
- * external symbols are located outside the parent object (where the parent
- * object is either vmlinux or the kmod being patched).
- */
-static int klp_find_external_symbol(struct module *pmod, const char *name,
-				    unsigned long *addr)
+static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
 {
-	const struct kernel_symbol *sym;
-
-	/* first, check if it's an exported symbol */
-	preempt_disable();
-	sym = find_symbol(name, NULL, NULL, true, true);
-	if (sym) {
-		*addr = sym->value;
-		preempt_enable();
-		return 0;
-	}
-	preempt_enable();
+	int i, cnt, vmlinux, ret;
+	char objname[MODULE_NAME_LEN];
+	char symname[KSYM_NAME_LEN];
+	char *strtab = pmod->core_kallsyms.strtab;
+	Elf_Rela *relas;
+	Elf_Sym *sym;
+	unsigned long sympos, addr;
 
 	/*
-	 * Check if it's in another .o within the patch module. This also
-	 * checks that the external symbol is unique.
+	 * Since the field widths for objname and symname in the sscanf()
+	 * call are hard-coded and correspond to MODULE_NAME_LEN and
+	 * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
+	 * and KSYM_NAME_LEN have the values we expect them to have.
+	 *
+	 * Because the value of MODULE_NAME_LEN can differ among architectures,
+	 * we use the smallest/strictest upper bound possible (56, based on
+	 * the current definition of MODULE_NAME_LEN) to prevent overflows.
 	 */
-	return klp_find_object_symbol(pmod->name, name, 0, addr);
+	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
+
+	relas = (Elf_Rela *) relasec->sh_addr;
+	/* For each rela in this klp relocation section */
+	for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
+		sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
+		if (sym->st_shndx != SHN_LIVEPATCH) {
+			pr_err("symbol %s is not marked as a livepatch symbol",
+			       strtab + sym->st_name);
+			return -EINVAL;
+		}
+
+		/* Format: .klp.sym.objname.symname,sympos */
+		cnt = sscanf(strtab + sym->st_name,
+			     ".klp.sym.%55[^.].%127[^,],%lu",
+			     objname, symname, &sympos);
+		if (cnt != 3) {
+			pr_err("symbol %s has an incorrectly formatted name",
+			       strtab + sym->st_name);
+			return -EINVAL;
+		}
+
+		/* klp_find_object_symbol() treats a NULL objname as vmlinux */
+		vmlinux = !strcmp(objname, "vmlinux");
+		ret = klp_find_object_symbol(vmlinux ? NULL : objname,
+					     symname, sympos, &addr);
+		if (ret)
+			return ret;
+
+		sym->st_value = addr;
+	}
+
+	return 0;
 }
 
 static int klp_write_object_relocations(struct module *pmod,
 					struct klp_object *obj)
 {
-	int ret = 0;
-	unsigned long val;
-	struct klp_reloc *reloc;
+	int i, cnt, ret = 0;
+	const char *objname, *secname;
+	char sec_objname[MODULE_NAME_LEN];
+	Elf_Shdr *sec;
 
 	if (WARN_ON(!klp_is_object_loaded(obj)))
 		return -EINVAL;
 
-	if (WARN_ON(!obj->relocs))
-		return -EINVAL;
+	objname = klp_is_module(obj) ? obj->name : "vmlinux";
 
 	module_disable_ro(pmod);
+	/* For each klp relocation section */
+	for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
+		sec = pmod->klp_info->sechdrs + i;
+		secname = pmod->klp_info->secstrings + sec->sh_name;
+		if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
+			continue;
 
-	for (reloc = obj->relocs; reloc->name; reloc++) {
-		/* discover the address of the referenced symbol */
-		if (reloc->external) {
-			if (reloc->sympos > 0) {
-				pr_err("non-zero sympos for external reloc symbol '%s' is not supported\n",
-				       reloc->name);
-				ret = -EINVAL;
-				goto out;
-			}
-			ret = klp_find_external_symbol(pmod, reloc->name, &val);
-		} else
-			ret = klp_find_object_symbol(obj->name,
-						     reloc->name,
-						     reloc->sympos,
-						     &val);
+		/*
+		 * Format: .klp.rela.sec_objname.section_name
+		 * See comment in klp_resolve_symbols() for an explanation
+		 * of the selected field width value.
+		 */
+		cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
+		if (cnt != 1) {
+			pr_err("section %s has an incorrectly formatted name",
+			       secname);
+			ret = -EINVAL;
+			break;
+		}
+
+		if (strcmp(objname, sec_objname))
+			continue;
+
+		ret = klp_resolve_symbols(sec, pmod);
 		if (ret)
-			goto out;
+			break;
 
-		ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
-					     val + reloc->addend);
-		if (ret) {
-			pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
-			       reloc->name, val, ret);
-			goto out;
-		}
+		ret = apply_relocate_add(pmod->klp_info->sechdrs,
+					 pmod->core_kallsyms.strtab,
+					 pmod->klp_info->symndx, i, pmod);
+		if (ret)
+			break;
 	}
 
-out:
 	module_enable_ro(pmod);
 	return ret;
 }
@@ -298,6 +334,19 @@ static void notrace klp_ftrace_handler(unsigned long ip,
 	rcu_read_unlock();
 }
 
+/*
+ * Convert a function address into the appropriate ftrace location.
+ *
+ * Usually this is just the address of the function, but on some architectures
+ * it's more complicated so allow them to provide a custom behaviour.
+ */
+#ifndef klp_get_ftrace_location
+static unsigned long klp_get_ftrace_location(unsigned long faddr)
+{
+	return faddr;
+}
+#endif
+
 static void klp_disable_func(struct klp_func *func)
 {
 	struct klp_ops *ops;
@@ -312,8 +361,14 @@ static void klp_disable_func(struct klp_func *func)
 		return;
 
 	if (list_is_singular(&ops->func_stack)) {
+		unsigned long ftrace_loc;
+
+		ftrace_loc = klp_get_ftrace_location(func->old_addr);
+		if (WARN_ON(!ftrace_loc))
+			return;
+
 		WARN_ON(unregister_ftrace_function(&ops->fops));
-		WARN_ON(ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0));
+		WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
 
 		list_del_rcu(&func->stack_node);
 		list_del(&ops->node);
@@ -338,6 +393,15 @@ static int klp_enable_func(struct klp_func *func)
 
 	ops = klp_find_ops(func->old_addr);
 	if (!ops) {
+		unsigned long ftrace_loc;
+
+		ftrace_loc = klp_get_ftrace_location(func->old_addr);
+		if (!ftrace_loc) {
+			pr_err("failed to find location for function '%s'\n",
+				func->old_name);
+			return -EINVAL;
+		}
+
 		ops = kzalloc(sizeof(*ops), GFP_KERNEL);
 		if (!ops)
 			return -ENOMEM;
@@ -352,7 +416,7 @@ static int klp_enable_func(struct klp_func *func)
 		INIT_LIST_HEAD(&ops->func_stack);
 		list_add_rcu(&func->stack_node, &ops->func_stack);
 
-		ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 0, 0);
+		ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
 		if (ret) {
 			pr_err("failed to set ftrace filter for function '%s' (%d)\n",
 			       func->old_name, ret);
@@ -363,7 +427,7 @@ static int klp_enable_func(struct klp_func *func)
 		if (ret) {
 			pr_err("failed to register ftrace handler for function '%s' (%d)\n",
 			       func->old_name, ret);
-			ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
+			ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
 			goto err;
 		}
 
@@ -683,6 +747,9 @@ static void klp_free_patch(struct klp_patch *patch)
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 {
+	if (!func->old_name || !func->new_func)
+		return -EINVAL;
+
 	INIT_LIST_HEAD(&func->stack_node);
 	func->state = KLP_DISABLED;
 
@@ -703,11 +770,9 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	struct klp_func *func;
 	int ret;
 
-	if (obj->relocs) {
-		ret = klp_write_object_relocations(patch->mod, obj);
-		if (ret)
-			return ret;
-	}
+	ret = klp_write_object_relocations(patch->mod, obj);
+	if (ret)
+		return ret;
 
 	klp_for_each_func(obj, func) {
 		ret = klp_find_object_symbol(obj->name, func->old_name,
@@ -842,12 +907,18 @@ int klp_register_patch(struct klp_patch *patch)
 {
 	int ret;
 
-	if (!klp_initialized())
-		return -ENODEV;
-
 	if (!patch || !patch->mod)
 		return -EINVAL;
 
+	if (!is_livepatch_module(patch->mod)) {
+		pr_err("module %s is not marked as a livepatch module",
+		       patch->mod->name);
+		return -EINVAL;
+	}
+
+	if (!klp_initialized())
+		return -ENODEV;
+
 	/*
 	 * 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

kernel/module.c

@@ -1973,6 +1973,83 @@ static void module_enable_nx(const struct module *mod) { }
 static void module_disable_nx(const struct module *mod) { }
 #endif
 
+#ifdef CONFIG_LIVEPATCH
+/*
+ * Persist Elf information about a module. Copy the Elf header,
+ * section header table, section string table, and symtab section
+ * index from info to mod->klp_info.
+ */
+static int copy_module_elf(struct module *mod, struct load_info *info)
+{
+	unsigned int size, symndx;
+	int ret;
+
+	size = sizeof(*mod->klp_info);
+	mod->klp_info = kmalloc(size, GFP_KERNEL);
+	if (mod->klp_info == NULL)
+		return -ENOMEM;
+
+	/* Elf header */
+	size = sizeof(mod->klp_info->hdr);
+	memcpy(&mod->klp_info->hdr, info->hdr, size);
+
+	/* Elf section header table */
+	size = sizeof(*info->sechdrs) * info->hdr->e_shnum;
+	mod->klp_info->sechdrs = kmalloc(size, GFP_KERNEL);
+	if (mod->klp_info->sechdrs == NULL) {
+		ret = -ENOMEM;
+		goto free_info;
+	}
+	memcpy(mod->klp_info->sechdrs, info->sechdrs, size);
+
+	/* Elf section name string table */
+	size = info->sechdrs[info->hdr->e_shstrndx].sh_size;
+	mod->klp_info->secstrings = kmalloc(size, GFP_KERNEL);
+	if (mod->klp_info->secstrings == NULL) {
+		ret = -ENOMEM;
+		goto free_sechdrs;
+	}
+	memcpy(mod->klp_info->secstrings, info->secstrings, size);
+
+	/* Elf symbol section index */
+	symndx = info->index.sym;
+	mod->klp_info->symndx = symndx;
+
+	/*
+	 * For livepatch modules, core_kallsyms.symtab is a complete
+	 * copy of the original symbol table. Adjust sh_addr to point
+	 * to core_kallsyms.symtab since the copy of the symtab in module
+	 * init memory is freed at the end of do_init_module().
+	 */
+	mod->klp_info->sechdrs[symndx].sh_addr = \
+		(unsigned long) mod->core_kallsyms.symtab;
+
+	return 0;
+
+free_sechdrs:
+	kfree(mod->klp_info->sechdrs);
+free_info:
+	kfree(mod->klp_info);
+	return ret;
+}
+
+static void free_module_elf(struct module *mod)
+{
+	kfree(mod->klp_info->sechdrs);
+	kfree(mod->klp_info->secstrings);
+	kfree(mod->klp_info);
+}
+#else /* !CONFIG_LIVEPATCH */
+static int copy_module_elf(struct module *mod, struct load_info *info)
+{
+	return 0;
+}
+
+static void free_module_elf(struct module *mod)
+{
+}
+#endif /* CONFIG_LIVEPATCH */
+
 void __weak module_memfree(void *module_region)
 {
 	vfree(module_region);
@@ -2011,6 +2088,9 @@ static void free_module(struct module *mod)
 	/* Free any allocated parameters. */
 	destroy_params(mod->kp, mod->num_kp);
 
+	if (is_livepatch_module(mod))
+		free_module_elf(mod);
+
 	/* Now we can delete it from the lists */
 	mutex_lock(&module_mutex);
 	/* Unlink carefully: kallsyms could be walking list. */
@@ -2126,6 +2206,10 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
 			       (long)sym[i].st_value);
 			break;
 
+		case SHN_LIVEPATCH:
+			/* Livepatch symbols are resolved by livepatch */
+			break;
+
 		case SHN_UNDEF:
 			ksym = resolve_symbol_wait(mod, info, name);
 			/* Ok if resolved.  */
@@ -2174,6 +2258,10 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
 		if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
 			continue;
 
+		/* Livepatch relocation sections are applied by livepatch */
+		if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
+			continue;
+
 		if (info->sechdrs[i].sh_type == SHT_REL)
 			err = apply_relocate(info->sechdrs, info->strtab,
 					     info->index.sym, i, mod);
@@ -2469,7 +2557,7 @@ static void layout_symtab(struct module *mod, struct load_info *info)
 
 	/* Compute total space required for the core symbols' strtab. */
 	for (ndst = i = 0; i < nsrc; i++) {
-		if (i == 0 ||
+		if (i == 0 || is_livepatch_module(mod) ||
 		    is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
 				   info->index.pcpu)) {
 			strtab_size += strlen(&info->strtab[src[i].st_name])+1;
@@ -2528,7 +2616,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 	mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs;
 	src = mod->kallsyms->symtab;
 	for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) {
-		if (i == 0 ||
+		if (i == 0 || is_livepatch_module(mod) ||
 		    is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
 				   info->index.pcpu)) {
 			dst[ndst] = src[i];
@@ -2667,6 +2755,26 @@ static int copy_chunked_from_user(void *dst, const void __user *usrc, unsigned l
 	return 0;
 }
 
+#ifdef CONFIG_LIVEPATCH
+static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
+{
+	mod->klp = get_modinfo(info, "livepatch") ? true : false;
+
+	return 0;
+}
+#else /* !CONFIG_LIVEPATCH */
+static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
+{
+	if (get_modinfo(info, "livepatch")) {
+		pr_err("%s: module is marked as livepatch module, but livepatch support is disabled",
+		       mod->name);
+		return -ENOEXEC;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_LIVEPATCH */
+
 /* Sets info->hdr and info->len. */
 static int copy_module_from_user(const void __user *umod, unsigned long len,
 				  struct load_info *info)
@@ -2821,6 +2929,10 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
 			"is unknown, you have been warned.\n", mod->name);
 	}
 
+	err = find_livepatch_modinfo(mod, info);
+	if (err)
+		return err;
+
 	/* Set up license info based on the info section */
 	set_license(mod, get_modinfo(info, "license"));
 
@@ -3494,6 +3606,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	if (err < 0)
 		goto coming_cleanup;
 
+	if (is_livepatch_module(mod)) {
+		err = copy_module_elf(mod, info);
+		if (err < 0)
+			goto sysfs_cleanup;
+	}
+
 	/* Get rid of temporary copy. */
 	free_copy(info);
 
@@ -3502,11 +3620,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
 
 	return do_init_module(mod);
 
+ sysfs_cleanup:
+	mod_sysfs_teardown(mod);
  coming_cleanup:
 	blocking_notifier_call_chain(&module_notify_list,
 				     MODULE_STATE_GOING, mod);
 	klp_module_going(mod);
-
  bug_cleanup:
 	/* module_bug_cleanup needs module_mutex protection */
 	mutex_lock(&module_mutex);

kernel/trace/ftrace.c

@@ -1530,7 +1530,19 @@ static int ftrace_cmp_recs(const void *a, const void *b)
 	return 0;
 }
 
-static unsigned long ftrace_location_range(unsigned long start, unsigned long end)
+/**
+ * ftrace_location_range - return the first address of a traced location
+ *	if it touches the given ip range
+ * @start: start of range to search.
+ * @end: end of range to search (inclusive). @end points to the last byte
+ *	to check.
+ *
+ * Returns rec->ip if the related ftrace location is a least partly within
+ * the given address range. That is, the first address of the instruction
+ * that is either a NOP or call to the function tracer. It checks the ftrace
+ * internal tables to determine if the address belongs or not.
+ */
+unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 {
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;

samples/livepatch/livepatch-sample.c

@@ -89,3 +89,4 @@ static void livepatch_exit(void)
 module_init(livepatch_init);
 module_exit(livepatch_exit);
 MODULE_LICENSE("GPL");
+MODULE_INFO(livepatch, "Y");