[PATCHv6 0/3] Kernel Live Patching

[PATCHv6 0/3] Kernel Live Patching

[Josh Poimboeuf]

Thanks for all the patches and comments for v5.  Seth is out this week,
so I'm sending this latest patch set in his absence.

Changelog:

changes in v6:
- add empty patch release function
- Petr's patches 2-5:
  - do not quietly ignore wrong usage
  - find and verify the old address in klp_*_init()
  - clean up ordering of functions
  - split init and free code that is done only for loaded modules
- minor cleanups

changes in v5:
- TODO: set IPMODIFY
- Mira and Petr patches
- add livepatch subdir to samples Makefile
- kernel-doc for internal struct fields and other cleanups (colons)
- s/klp_find_symbol/klp_find_object_symbol/
- remove redundant error checks
- protect API functions from init failure
- protect API functions from unregistered patches
- return -EBUSY in klp_unregister_patch()
- remove unneeded comments
- propagate error in klp_init_objects()
- s/free/err/ for error handling labels
- fix broken patch release handling
- add asm/livepatch.h and asm/elf.h includes
- add comment for numpages
- handle NULL obj->name in kobject_create_and_add()
- add notrace to ftrace handler
- mutex protect all of klp_init_patch()
- generate compile error when asm/livepatch.h included but disabled
- add WARN_ON checks
- rename struct klp_reloc fields
- make readonly bool and optimize
- smaller cleanups

changes in v4:
- TODO: set IPMODIFY (Masami patch heading to -next)
- kernel-doc for structures
- dynamically allocate ftrace ops (add ktype and release for func)
- add sample live patch module
- add CC_USING_FENTRY check
- s/LPC_/KLP_/
- objname NULL for vmlinux rather than "vmlinux"
- remove module unload code and licensing (since we are builtin now)
- remove code section headers
- narrow mutex hold to only include list_add() in register path
- split WARN_ON with compound condition
- add inline to static function defined in header file

changes in v3:
- TODO: FTRACE_OPS_FL_DYNAMIC? allocate fops in core?
- TODO: kernel-doc for API structs once agreed upon
- merge API and core data structures (Miroslav)
- replace lp_ and lpc_ prefixes with klp_
- add ARCH_HAVE_LIVE_PATCHING
- guard livepatch.h content with IS_ENABLED(CONFIG_LIVE_PATCHING)
- smaller cleanups

changes in v2:
- TODO: kernel-doc for API structs once agreed upon
- rebase to next-20141113
- add copyright/license block to livepatch.h
- add _LINUX prefix to header defines
- replace semaphore with mutex
- add LPC_ prefix to state enum
- convert BUGs to WARNs and handle properly
- change Kconfig default to n
- remove [old|new] attrs from function sysfs dir (KASLR leak, no use)
- disregard user provided old_addr if kernel uses KASLR
- s/out/err for error path labels
- s/unregister/disable for uniform terminology
- s/lp/lpc for module notifier elements
- replace module ref'ing with unload notifier + mutex protection
- adjust notifier priority to run before ftrace
- make LIVE_PATCHING boolean (about to depend on arch stuff)
- move x86-specific reloc code to arch/x86
- s/dynrela/reloc/
- add live patching sysfs documentation
- add API function kernel-doc

Summary:

This patchset implements an ftrace-based mechanism and kernel interface for
doing live patching of kernel and kernel module functions.  It represents the
greatest common functionality set between kpatch [1] and kGraft [2] and can
accept patches built using either method.  This solution was discussed in the
Live Patching Mini-conference at LPC 2014 [3].

The model consists of a live patching "core" that provides an interface for
other "patch" kernel modules to register patches with the core.

Patch modules contain the new function code and create an klp_patch structure
containing the required data about what functions to patch, where the new code
for each patched function resides, and in which kernel object (vmlinux or
module) the function to be patch resides.  The patch module then invokes the
klp_register_patch() function to register with the core, then klp_enable_patch()
to have the core redirect the execution paths using ftrace.

The live patching core creates a sysfs hierarchy for user-level access to live
patching information.  The hierarchy is structured like this:

/sys/kernel/livepatch
/sys/kernel/livepatch/<patch>
/sys/kernel/livepatch/<patch>/enabled
/sys/kernel/livepatch/<patch>/<object>
/sys/kernel/livepatch/<patch>/<object>/<func>

The old function is located using one of two methods: it is either provided by
the patch module (only possible for a function in vmlinux) or kallsyms lookup.
Symbol ambiguity results in a failure.

The core takes a reference on the patch module itself to keep it from
unloading.  This is because, without a mechanism to ensure that no thread is
currently executing in the patched function, we can not determine whether it is
safe to unload the patch module.  For this reason, unloading patch modules is
currently not allowed.

Disabling patches can be done using the "enabled" attribute of the patch:

echo 0 > /sys/kernel/livepatch/<patch>/enabled

If a patch module contains a patch for a module that is not currently loaded,
there is nothing to patch so the core does nothing for that patch object.
However, the core registers a module notifier that looks for COMING events so
that if the module is ever loaded, it is immediately patched.  If a module with
patch code is removed, the notifier looks for GOING events and disables any
patched functions for that object before it unloads.  The notifier has a higher
priority than that of the ftrace notifier so that it runs before the ftrace
notifier for GOING events and we can cleanly unregister from ftrace.

kpatch and kGraft each have their own mechanisms for ensuring system
consistency during the patching process. This first version does not implement
any consistency mechanism that ensures that old and new code do not run
together.  In practice, ~90% of CVEs are safe to apply in this way, since they
simply add a conditional check.  However, any function change that can not
execute safely with the old version of the function can _not_ be safely applied
for now.

[1] https://github.com/dynup/kpatch
[2] https://git.kernel.org/cgit/linux/kernel/git/jirislaby/kgraft.git/
[3] https://etherpad.fr/p/LPC2014_LivePatching

Seth Jennings (3):
  kernel: add TAINT_LIVEPATCH
  kernel: add support for live patching
  samples: add sample live patching module

 Documentation/ABI/testing/sysfs-kernel-livepatch |  44 ++
 Documentation/oops-tracing.txt                   |   2 +
 Documentation/sysctl/kernel.txt                  |   1 +
 MAINTAINERS                                      |  14 +
 arch/x86/Kconfig                                 |   3 +
 arch/x86/include/asm/livepatch.h                 |  36 +
 arch/x86/kernel/Makefile                         |   1 +
 arch/x86/kernel/livepatch.c                      |  89 +++
 include/linux/kernel.h                           |   1 +
 include/linux/livepatch.h                        | 132 ++++
 kernel/Makefile                                  |   1 +
 kernel/livepatch/Kconfig                         |  18 +
 kernel/livepatch/Makefile                        |   3 +
 kernel/livepatch/core.c                          | 935 +++++++++++++++++++++++
 kernel/panic.c                                   |   2 +
 samples/Kconfig                                  |   7 +
 samples/Makefile                                 |   2 +-
 samples/livepatch/Makefile                       |   1 +
 samples/livepatch/livepatch-sample.c             |  87 +++
 19 files changed, 1378 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-livepatch
 create mode 100644 arch/x86/include/asm/livepatch.h
 create mode 100644 arch/x86/kernel/livepatch.c
 create mode 100644 include/linux/livepatch.h
 create mode 100644 kernel/livepatch/Kconfig
 create mode 100644 kernel/livepatch/Makefile
 create mode 100644 kernel/livepatch/core.c
 create mode 100644 samples/livepatch/Makefile
 create mode 100644 samples/livepatch/livepatch-sample.c

-- 
2.1.0

[PATCHv6 1/3] kernel: add TAINT_LIVEPATCH

[Josh Poimboeuf]

From: Seth Jennings <sjenning@redhat.com>

This adds a new taint flag to indicate when the kernel or a kernel
module has been live patched.  This will provide a clean indication in
bug reports that live patching was used.

Additionally, if the crash occurs in a live patched function, the live
patch module will appear beside the patched function in the backtrace.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
---
 Documentation/oops-tracing.txt  | 2 ++
 Documentation/sysctl/kernel.txt | 1 +
 include/linux/kernel.h          | 1 +
 kernel/panic.c                  | 2 ++
 4 files changed, 6 insertions(+)

diff --git a/Documentation/oops-tracing.txt b/Documentation/oops-tracing.txt
index beefb9f..f3ac05c 100644
--- a/Documentation/oops-tracing.txt
+++ b/Documentation/oops-tracing.txt
@@ -270,6 +270,8 @@ characters, each representing a particular tainted value.
 
  15: 'L' if a soft lockup has previously occurred on the system.
 
+ 16: 'K' if the kernel has been live patched.
+
 The primary reason for the 'Tainted: ' string is to tell kernel
 debuggers if this is a clean kernel or if anything unusual has
 occurred.  Tainting is permanent: even if an offending module is
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 75511ef..83ab256 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -843,6 +843,7 @@ can be ORed together:
 8192 - An unsigned module has been loaded in a kernel supporting module
        signature.
 16384 - A soft lockup has previously occurred on the system.
+32768 - The kernel has been live patched.
 
 ==============================================================
 
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 5449d2f..d03e3de 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -471,6 +471,7 @@ extern enum system_states {
 #define TAINT_OOT_MODULE		12
 #define TAINT_UNSIGNED_MODULE		13
 #define TAINT_SOFTLOCKUP		14
+#define TAINT_LIVEPATCH			15
 
 extern const char hex_asc[];
 #define hex_asc_lo(x)	hex_asc[((x) & 0x0f)]
diff --git a/kernel/panic.c b/kernel/panic.c
index 4d8d6f9..8136ad7 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -226,6 +226,7 @@ static const struct tnt tnts[] = {
 	{ TAINT_OOT_MODULE,		'O', ' ' },
 	{ TAINT_UNSIGNED_MODULE,	'E', ' ' },
 	{ TAINT_SOFTLOCKUP,		'L', ' ' },
+	{ TAINT_LIVEPATCH,		'K', ' ' },
 };
 
 /**
@@ -246,6 +247,7 @@ static const struct tnt tnts[] = {
  *  'O' - Out-of-tree module has been loaded.
  *  'E' - Unsigned module has been loaded.
  *  'L' - A soft lockup has previously occurred.
+ *  'K' - Kernel has been live patched.
  *
  *	The string is overwritten by the next call to print_tainted().
  */
-- 
2.1.0

[PATCHv6 2/3] kernel: add support for live patching

[Josh Poimboeuf]

From: Seth Jennings <sjenning@redhat.com>

This commit introduces code for the live patching core.  It implements
an ftrace-based mechanism and kernel interface for doing live patching
of kernel and kernel module functions.

It represents the greatest common functionality set between kpatch and
kgraft and can accept patches built using either method.

This first version does not implement any consistency mechanism that
ensures that old and new code do not run together.  In practice, ~90% of
CVEs are safe to apply in this way, since they simply add a conditional
check.  However, any function change that can not execute safely with
the old version of the function can _not_ be safely applied in this
version.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 Documentation/ABI/testing/sysfs-kernel-livepatch |  44 ++
 MAINTAINERS                                      |  13 +
 arch/x86/Kconfig                                 |   3 +
 arch/x86/include/asm/livepatch.h                 |  36 +
 arch/x86/kernel/Makefile                         |   1 +
 arch/x86/kernel/livepatch.c                      |  89 +++
 include/linux/livepatch.h                        | 132 ++++
 kernel/Makefile                                  |   1 +
 kernel/livepatch/Kconfig                         |  18 +
 kernel/livepatch/Makefile                        |   3 +
 kernel/livepatch/core.c                          | 935 +++++++++++++++++++++++
 11 files changed, 1275 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-livepatch
 create mode 100644 arch/x86/include/asm/livepatch.h
 create mode 100644 arch/x86/kernel/livepatch.c
 create mode 100644 include/linux/livepatch.h
 create mode 100644 kernel/livepatch/Kconfig
 create mode 100644 kernel/livepatch/Makefile
 create mode 100644 kernel/livepatch/core.c

diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
new file mode 100644
index 0000000..5bf42a8
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -0,0 +1,44 @@
+What:		/sys/kernel/livepatch
+Date:		Nov 2014
+KernelVersion:	3.19.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		Interface for kernel live patching
+
+		The /sys/kernel/livepatch directory contains subdirectories for
+		each loaded live patch module.
+
+What:		/sys/kernel/livepatch/<patch>
+Date:		Nov 2014
+KernelVersion:	3.19.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		The patch directory contains subdirectories for each kernel
+		object (vmlinux or a module) in which it patched functions.
+
+What:		/sys/kernel/livepatch/<patch>/enabled
+Date:		Nov 2014
+KernelVersion:	3.19.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		A writable attribute that indicates whether the patched
+		code is currently applied.  Writing 0 will disable the patch
+		while writing 1 will re-enable the patch.
+
+What:		/sys/kernel/livepatch/<patch>/<object>
+Date:		Nov 2014
+KernelVersion:	3.19.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		The object directory contains subdirectories for each function
+		that is patched within the object.
+
+What:		/sys/kernel/livepatch/<patch>/<object>/<function>
+Date:		Nov 2014
+KernelVersion:	3.19.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		The function directory contains attributes regarding the
+		properties and state of the patched function.
+
+		There are currently no such attributes.
diff --git a/MAINTAINERS b/MAINTAINERS
index 06d5b4b..94f9f69 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5777,6 +5777,19 @@ F:	Documentation/misc-devices/lis3lv02d
 F:	drivers/misc/lis3lv02d/
 F:	drivers/platform/x86/hp_accel.c
 
+LIVE PATCHING
+M:	Josh Poimboeuf <jpoimboe@redhat.com>
+M:	Seth Jennings <sjenning@redhat.com>
+M:	Jiri Kosina <jkosina@suse.cz>
+M:	Vojtech Pavlik <vojtech@suse.cz>
+S:	Maintained
+F:	kernel/livepatch/
+F:	include/linux/livepatch.h
+F:	arch/x86/include/asm/livepatch.h
+F:	arch/x86/kernel/livepatch.c
+F:	Documentation/ABI/testing/sysfs-kernel-livepatch
+L:	live-patching@vger.kernel.org
+
 LLC (802.2)
 M:	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
 S:	Maintained
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ce8dcdf..5c57181 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -17,6 +17,7 @@ config X86_64
 	depends on 64BIT
 	select X86_DEV_DMA_OPS
 	select ARCH_USE_CMPXCHG_LOCKREF
+	select ARCH_HAVE_LIVE_PATCHING
 
 ### Arch settings
 config X86
@@ -1986,6 +1987,8 @@ config CMDLINE_OVERRIDE
 	  This is used to work around broken boot loaders.  This should
 	  be set to 'N' under normal conditions.
 
+source "kernel/livepatch/Kconfig"
+
 endmenu
 
 config ARCH_ENABLE_MEMORY_HOTPLUG
diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
new file mode 100644
index 0000000..c2ae592
--- /dev/null
+++ b/arch/x86/include/asm/livepatch.h
@@ -0,0 +1,36 @@
+/*
+ * livepatch.h - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _ASM_X86_LIVEPATCH_H
+#define _ASM_X86_LIVEPATCH_H
+
+#include <linux/module.h>
+
+#ifdef CONFIG_LIVE_PATCHING
+#ifndef CC_USING_FENTRY
+#error Your compiler must support -mfentry for live patching to work
+#endif
+extern int klp_write_module_reloc(struct module *mod, unsigned long type,
+				  unsigned long loc, unsigned long value);
+
+#else
+#error Live patching support is disabled; check CONFIG_LIVE_PATCHING
+#endif
+
+#endif /* _ASM_X86_LIVEPATCH_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 5d4502c..316b34e 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -63,6 +63,7 @@ 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_LIVE_PATCHING)	+= livepatch.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
 obj-$(CONFIG_X86_TSC)		+= trace_clock.o
diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
new file mode 100644
index 0000000..4b0ed7b
--- /dev/null
+++ b/arch/x86/kernel/livepatch.c
@@ -0,0 +1,89 @@
+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <asm/cacheflush.h>
+#include <asm/page_types.h>
+#include <asm/elf.h>
+#include <asm/livepatch.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)
+{
+	int ret, numpages, size = 4;
+	bool readonly;
+	unsigned long val;
+	unsigned long core = (unsigned long)mod->module_core;
+	unsigned long core_ro_size = mod->core_ro_size;
+	unsigned long core_size = mod->core_size;
+
+	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;
+	}
+
+	if (loc < core || loc >= core + core_size)
+		/* loc does not point to any symbol inside the module */
+		return -EINVAL;
+
+	if (loc < core + core_ro_size)
+		readonly = true;
+	else
+		readonly = false;
+
+	/* determine if the relocation spans a page boundary */
+	numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
+
+	if (readonly)
+		set_memory_rw(loc & PAGE_MASK, numpages);
+
+	ret = probe_kernel_write((void *)loc, &val, size);
+
+	if (readonly)
+		set_memory_ro(loc & PAGE_MASK, numpages);
+
+	return ret;
+}
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
new file mode 100644
index 0000000..b61fe74
--- /dev/null
+++ b/include/linux/livepatch.h
@@ -0,0 +1,132 @@
+/*
+ * livepatch.h - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _LINUX_LIVEPATCH_H_
+#define _LINUX_LIVEPATCH_H_
+
+#include <linux/module.h>
+#include <linux/ftrace.h>
+
+#if IS_ENABLED(CONFIG_LIVE_PATCHING)
+
+#include <asm/livepatch.h>
+
+enum klp_state {
+	KLP_DISABLED,
+	KLP_ENABLED
+};
+
+/**
+ * struct klp_func - function structure for live patching
+ * @old_name:	name of the function to be patched
+ * @new_func:	pointer to the patched function code
+ * @old_addr:	a hint conveying at what address the old function
+ *		can be found (optional, vmlinux patches only)
+ * @kobj:	kobject for sysfs resources
+ * @fops:	ftrace operations structure
+ * @state:	tracks function-level patch application state
+ */
+struct klp_func {
+	/* external */
+	const char *old_name;
+	void *new_func;
+	/*
+	 * The old_addr field is optional and can be used to resolve
+	 * duplicate symbol names in the vmlinux object.  If this
+	 * information is not present, the symbol is located by name
+	 * with kallsyms. If the name is not unique and old_addr is
+	 * not provided, the patch application fails as there is no
+	 * way to resolve the ambiguity.
+	 */
+	unsigned long old_addr;
+
+	/* internal */
+	struct kobject kobj;
+	struct ftrace_ops *fops;
+	enum klp_state state;
+};
+
+/**
+ * struct klp_reloc - relocation structure for live patching
+ * @loc:	address where the relocation will be written
+ * @val:	address of the referenced symbol (optional,
+ *		vmlinux	patches only)
+ * @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 val;
+	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
+ * 		(NULL for vmlinux)
+ * @state:	tracks object-level patch application state
+ */
+struct klp_object {
+	/* external */
+	const char *name;
+	struct klp_reloc *relocs;
+	struct klp_func *funcs;
+
+	/* internal */
+	struct kobject *kobj;
+	struct module *mod;
+	enum klp_state state;
+};
+
+/**
+ * struct klp_patch - patch structure for live patching
+ * @mod:	reference to the live patch module
+ * @objs:	object entries for kernel objects to be patched
+ * @list:	list node for global list of registered patches
+ * @kobj:	kobject for sysfs resources
+ * @state:	tracks patch-level application state
+ */
+struct klp_patch {
+	/* external */
+	struct module *mod;
+	struct klp_object *objs;
+
+	/* internal */
+	struct list_head list;
+	struct kobject kobj;
+	enum klp_state state;
+};
+
+extern int klp_register_patch(struct klp_patch *);
+extern int klp_unregister_patch(struct klp_patch *);
+extern int klp_enable_patch(struct klp_patch *);
+extern int klp_disable_patch(struct klp_patch *);
+
+#endif /* CONFIG_LIVE_PATCHING */
+
+#endif /* _LINUX_LIVEPATCH_H_ */
diff --git a/kernel/Makefile b/kernel/Makefile
index a59481a..616994f 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -26,6 +26,7 @@ obj-y += power/
 obj-y += printk/
 obj-y += irq/
 obj-y += rcu/
+obj-y += livepatch/
 
 obj-$(CONFIG_CHECKPOINT_RESTORE) += kcmp.o
 obj-$(CONFIG_FREEZER) += freezer.o
diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
new file mode 100644
index 0000000..96da00f
--- /dev/null
+++ b/kernel/livepatch/Kconfig
@@ -0,0 +1,18 @@
+config ARCH_HAVE_LIVE_PATCHING
+	boolean
+	help
+	  Arch supports kernel live patching
+
+config LIVE_PATCHING
+	boolean "Kernel Live Patching"
+	depends on DYNAMIC_FTRACE_WITH_REGS
+	depends on MODULES
+	depends on SYSFS
+	depends on KALLSYMS_ALL
+	depends on ARCH_HAVE_LIVE_PATCHING
+	help
+	  Say Y here if you want to support kernel live patching.
+	  This option has no runtime impact until a kernel "patch"
+	  module uses the interface provided by this option to register
+	  a patch, causing calls to patched functions to be redirected
+	  to new function code contained in the patch module.
diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
new file mode 100644
index 0000000..7c1f008
--- /dev/null
+++ b/kernel/livepatch/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_LIVE_PATCHING) += livepatch.o
+
+livepatch-objs := core.o
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
new file mode 100644
index 0000000..4ca924b
--- /dev/null
+++ b/kernel/livepatch/core.c
@@ -0,0 +1,935 @@
+/*
+ * core.c - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/ftrace.h>
+#include <linux/list.h>
+#include <linux/kallsyms.h>
+#include <linux/livepatch.h>
+
+/*
+ * The klp_mutex protects the klp_patches list and state transitions of any
+ * structure reachable from the patches list.  References to any structure must
+ * be obtained under mutex protection.
+ */
+
+static DEFINE_MUTEX(klp_mutex);
+static LIST_HEAD(klp_patches);
+
+static struct kobject *klp_root_kobj;
+
+static bool klp_is_module(struct klp_object *obj)
+{
+	return obj->name;
+}
+
+static bool klp_is_object_loaded(struct klp_object *obj)
+{
+	return !obj->name || obj->mod;
+}
+
+/* sets obj->mod if object is not vmlinux and module is found */
+static void klp_find_object_module(struct klp_object *obj)
+{
+	if (!klp_is_module(obj))
+		return;
+
+	mutex_lock(&module_mutex);
+	/*
+	 * We don't need to take a reference on the module here because we have
+	 * the klp_mutex, which is also taken by the module notifier.  This
+	 * prevents any module from unloading until we release the klp_mutex.
+	 */
+	obj->mod = find_module(obj->name);
+	mutex_unlock(&module_mutex);
+}
+
+/* klp_mutex must be held by caller */
+static bool klp_patch_is_registered(struct klp_patch *patch)
+{
+	struct klp_patch *mypatch;
+
+	list_for_each_entry(mypatch, &klp_patches, list)
+		if (mypatch == patch)
+			return true;
+
+	return false;
+}
+
+static bool klp_is_enabled(void)
+{
+	return klp_root_kobj;
+}
+
+struct klp_find_arg {
+	const char *objname;
+	const char *name;
+	unsigned long addr;
+	/*
+	 * If count == 0, the symbol was not found. If count == 1, a unique
+	 * match was found and addr is set.  If count > 1, there is
+	 * unresolvable ambiguity among "count" number of symbols with the same
+	 * name in the same object.
+	 */
+	unsigned long count;
+};
+
+static int klp_find_callback(void *data, const char *name,
+			     struct module *mod, unsigned long addr)
+{
+	struct klp_find_arg *args = data;
+
+	if ((mod && !args->objname) || (!mod && args->objname))
+		return 0;
+
+	if (strcmp(args->name, name))
+		return 0;
+
+	if (args->objname && strcmp(args->objname, mod->name))
+		return 0;
+
+	/*
+	 * args->addr might be overwritten if another match is found
+	 * but klp_find_object_symbol() handles this and only returns the
+	 * addr if count == 1.
+	 */
+	args->addr = addr;
+	args->count++;
+
+	return 0;
+}
+
+static int klp_find_object_symbol(const char *objname, const char *name,
+				  unsigned long *addr)
+{
+	struct klp_find_arg args = {
+		.objname = objname,
+		.name = name,
+		.addr = 0,
+		.count = 0
+	};
+
+	kallsyms_on_each_symbol(klp_find_callback, &args);
+
+	if (args.count == 0)
+		pr_err("symbol '%s' not found in symbol table\n", name);
+	else if (args.count > 1)
+		pr_err("unresolvable ambiguity (%lu matches) on symbol '%s' in object '%s'\n",
+		       args.count, name, objname);
+	else {
+		*addr = args.addr;
+		return 0;
+	}
+
+	*addr = 0;
+	return -EINVAL;
+}
+
+struct klp_verify_args {
+	const char *name;
+	const unsigned long addr;
+};
+
+static int klp_verify_callback(void *data, const char *name,
+			       struct module *mod, unsigned long addr)
+{
+	struct klp_verify_args *args = data;
+
+	if (!mod &&
+	    !strcmp(args->name, name) &&
+	    args->addr == addr)
+		return 1;
+
+	return 0;
+}
+
+static int klp_verify_vmlinux_symbol(const char *name, unsigned long addr)
+{
+	struct klp_verify_args args = {
+		.name = name,
+		.addr = addr,
+	};
+
+	if (kallsyms_on_each_symbol(klp_verify_callback, &args))
+		return 0;
+
+	pr_err("symbol '%s' not found at specified address 0x%016lx, kernel mismatch?",
+		name, addr);
+	return -EINVAL;
+}
+
+static int klp_find_verify_func_addr(struct klp_object *obj,
+				     struct klp_func *func)
+{
+	int ret;
+
+#if defined(CONFIG_RANDOMIZE_BASE)
+	/* KASLR is enabled, disregard old_addr from user */
+	func->old_addr = 0;
+#endif
+
+	if (!func->old_addr || klp_is_module(obj))
+		ret = klp_find_object_symbol(obj->name, func->old_name,
+					     &func->old_addr);
+	else
+		ret = klp_verify_vmlinux_symbol(func->old_name,
+						func->old_addr);
+
+	return ret;
+}
+
+/*
+ * 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)
+{
+	const struct kernel_symbol *sym;
+
+	/* first, check if it's an exported symbol */
+	preempt_disable();
+	sym = find_symbol(name, NULL, NULL, true, true);
+	preempt_enable();
+	if (sym) {
+		*addr = sym->value;
+		return 0;
+	}
+
+	/* otherwise check if it's in another .o within the patch module */
+	return klp_find_object_symbol(pmod->name, name, addr);
+}
+
+static int klp_write_object_relocations(struct module *pmod,
+					struct klp_object *obj)
+{
+	int ret;
+	struct klp_reloc *reloc;
+
+	if (WARN_ON(!klp_is_object_loaded(obj)))
+		return -EINVAL;
+
+	if (WARN_ON(!obj->relocs))
+		return -EINVAL;
+
+	for (reloc = obj->relocs; reloc->name; reloc++) {
+		if (!klp_is_module(obj)) {
+			ret = klp_verify_vmlinux_symbol(reloc->name,
+							reloc->val);
+			if (ret)
+				return ret;
+		} else {
+			/* module, reloc->val needs to be discovered */
+			if (reloc->external)
+				ret = klp_find_external_symbol(pmod,
+							       reloc->name,
+							       &reloc->val);
+			else
+				ret = klp_find_object_symbol(obj->mod->name,
+							     reloc->name,
+							     &reloc->val);
+			if (ret)
+				return ret;
+		}
+		ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
+					     reloc->val + reloc->addend);
+		if (ret) {
+			pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
+			       reloc->name, reloc->val, ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static void notrace klp_ftrace_handler(unsigned long ip,
+				       unsigned long parent_ip,
+				       struct ftrace_ops *ops,
+				       struct pt_regs *regs)
+{
+	struct klp_func *func = ops->private;
+
+	regs->ip = (unsigned long)func->new_func;
+}
+
+static int klp_disable_func(struct klp_func *func)
+{
+	int ret;
+
+	if (WARN_ON(func->state != KLP_ENABLED))
+		return -EINVAL;
+
+	if (WARN_ON(!func->old_addr))
+		return -EINVAL;
+
+	ret = unregister_ftrace_function(func->fops);
+	if (ret) {
+		pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
+		       func->old_name, ret);
+		return ret;
+	}
+
+	ret = ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
+	if (ret)
+		pr_warn("function unregister succeeded but failed to clear the filter\n");
+
+	func->state = KLP_DISABLED;
+
+	return 0;
+}
+
+static int klp_enable_func(struct klp_func *func)
+{
+	int ret;
+
+	if (WARN_ON(!func->old_addr))
+		return -EINVAL;
+
+	if (WARN_ON(func->state != KLP_DISABLED))
+		return -EINVAL;
+
+	ret = ftrace_set_filter_ip(func->fops, func->old_addr, 0, 0);
+	if (ret) {
+		pr_err("failed to set ftrace filter for function '%s' (%d)\n",
+		       func->old_name, ret);
+		return ret;
+	}
+
+	ret = register_ftrace_function(func->fops);
+	if (ret) {
+		pr_err("failed to register ftrace handler for function '%s' (%d)\n",
+		       func->old_name, ret);
+		ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
+	} else {
+		func->state = KLP_ENABLED;
+	}
+
+	return ret;
+}
+
+static int klp_disable_object(struct klp_object *obj)
+{
+	struct klp_func *func;
+	int ret;
+
+	if (WARN_ON(obj->state != KLP_ENABLED))
+		return -EINVAL;
+
+	for (func = obj->funcs; func->old_name; func++) {
+		if (func->state != KLP_ENABLED)
+			continue;
+
+		ret = klp_disable_func(func);
+		if (ret)
+			return ret;
+	}
+
+	obj->state = KLP_DISABLED;
+
+	return 0;
+}
+
+static int klp_enable_object(struct klp_object *obj)
+{
+	struct klp_func *func;
+	int ret;
+
+	if (WARN_ON(obj->state != KLP_DISABLED))
+		return -EINVAL;
+
+	if (WARN_ON(!klp_is_object_loaded(obj)))
+		return -EINVAL;
+
+	for (func = obj->funcs; func->old_name; func++) {
+		ret = klp_enable_func(func);
+		if (ret)
+			goto unregister;
+	}
+	obj->state = KLP_ENABLED;
+
+	return 0;
+
+unregister:
+	WARN_ON(klp_disable_object(obj));
+	return ret;
+}
+
+static int __klp_disable_patch(struct klp_patch *patch)
+{
+	struct klp_object *obj;
+	int ret;
+
+	if (WARN_ON(patch->state != KLP_ENABLED))
+		return -EINVAL;
+
+	pr_notice("disabling patch '%s'\n", patch->mod->name);
+
+	for (obj = patch->objs; obj->funcs; obj++) {
+		if (obj->state != KLP_ENABLED)
+			continue;
+
+		ret = klp_disable_object(obj);
+		if (ret)
+			return ret;
+	}
+
+	patch->state = KLP_DISABLED;
+
+	return 0;
+}
+
+/**
+ * klp_disable_patch() - disables a registered patch
+ * @patch:	The registered, enabled patch to be disabled
+ *
+ * Unregisters the patched functions from ftrace.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_disable_patch(struct klp_patch *patch)
+{
+	int ret;
+
+	if (!klp_is_enabled())
+		return -ENODEV;
+
+	mutex_lock(&klp_mutex);
+
+	if (!klp_patch_is_registered(patch)) {
+		ret = -EINVAL;
+		goto err;
+	}
+
+	ret = __klp_disable_patch(patch);
+
+err:
+	mutex_unlock(&klp_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(klp_disable_patch);
+
+static int __klp_enable_patch(struct klp_patch *patch)
+{
+	struct klp_object *obj;
+	int ret;
+
+	if (WARN_ON(patch->state != KLP_DISABLED))
+		return -EINVAL;
+
+	pr_notice_once("tainting kernel with TAINT_LIVEPATCH\n");
+	add_taint(TAINT_LIVEPATCH, LOCKDEP_STILL_OK);
+
+	pr_notice("enabling patch '%s'\n", patch->mod->name);
+
+	for (obj = patch->objs; obj->funcs; obj++) {
+		klp_find_object_module(obj);
+
+		if (!klp_is_object_loaded(obj))
+			continue;
+
+		ret = klp_enable_object(obj);
+		if (ret)
+			goto unregister;
+	}
+
+	patch->state = KLP_ENABLED;
+
+	return 0;
+
+unregister:
+	WARN_ON(__klp_disable_patch(patch));
+	return ret;
+}
+
+/**
+ * klp_enable_patch() - enables a registered patch
+ * @patch:	The registered, disabled patch to be enabled
+ *
+ * Performs the needed symbol lookups and code relocations,
+ * then registers the patched functions with ftrace.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_enable_patch(struct klp_patch *patch)
+{
+	int ret;
+
+	if (!klp_is_enabled())
+		return -ENODEV;
+
+	mutex_lock(&klp_mutex);
+
+	if (!klp_patch_is_registered(patch)) {
+		ret = -EINVAL;
+		goto err;
+	}
+
+	ret = __klp_enable_patch(patch);
+
+err:
+	mutex_unlock(&klp_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(klp_enable_patch);
+
+/*
+ * Sysfs Interface
+ *
+ * /sys/kernel/livepatch
+ * /sys/kernel/livepatch/<patch>
+ * /sys/kernel/livepatch/<patch>/enabled
+ * /sys/kernel/livepatch/<patch>/<object>
+ * /sys/kernel/livepatch/<patch>/<object>/<func>
+ */
+
+static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
+			     const char *buf, size_t count)
+{
+	struct klp_patch *patch;
+	int ret;
+	unsigned long val;
+
+	ret = kstrtoul(buf, 10, &val);
+	if (ret)
+		return -EINVAL;
+
+	if (val != KLP_DISABLED && val != KLP_ENABLED)
+		return -EINVAL;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+
+	mutex_lock(&klp_mutex);
+
+	if (val == patch->state) {
+		/* already in requested state */
+		ret = -EINVAL;
+		goto err;
+	}
+
+	if (val == KLP_ENABLED) {
+		ret = __klp_enable_patch(patch);
+		if (ret)
+			goto err;
+	} else {
+		ret = __klp_disable_patch(patch);
+		if (ret)
+			goto err;
+	}
+
+	mutex_unlock(&klp_mutex);
+
+	return count;
+
+err:
+	mutex_unlock(&klp_mutex);
+	return ret;
+}
+
+static ssize_t enabled_show(struct kobject *kobj,
+			    struct kobj_attribute *attr, char *buf)
+{
+	struct klp_patch *patch;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->state);
+}
+
+static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
+static struct attribute *klp_patch_attrs[] = {
+	&enabled_kobj_attr.attr,
+	NULL
+};
+
+static void klp_kobj_release_patch(struct kobject *kobj)
+{
+	/*
+	 * Once we have a consistency model we'll need to module_put() the
+	 * patch module here.  See klp_register_patch() for more details.
+	 */
+}
+
+static struct kobj_type klp_ktype_patch = {
+	.release = klp_kobj_release_patch,
+	.sysfs_ops = &kobj_sysfs_ops,
+	.default_attrs = klp_patch_attrs,
+};
+
+static void klp_kobj_release_func(struct kobject *kobj)
+{
+	struct klp_func *func;
+
+	func = container_of(kobj, struct klp_func, kobj);
+	kfree(func->fops);
+}
+
+static struct kobj_type klp_ktype_func = {
+	.release = klp_kobj_release_func,
+	.sysfs_ops = &kobj_sysfs_ops,
+};
+
+/*
+ * Free all functions' kobjects in the array up to some limit. When limit is
+ * NULL, all kobjects are freed.
+ */
+static void klp_free_funcs_limited(struct klp_object *obj,
+				   struct klp_func *limit)
+{
+	struct klp_func *func;
+
+	for (func = obj->funcs; func->old_name && func != limit; func++)
+		kobject_put(&func->kobj);
+}
+
+/* Clean up when a patched object is unloaded */
+static void klp_free_object_loaded(struct klp_object *obj)
+{
+	struct klp_func *func;
+
+	obj->mod = NULL;
+
+	for (func = obj->funcs; func->old_name; func++)
+		func->old_addr = 0;
+}
+
+/*
+ * Free all objects' kobjects in the array up to some limit. When limit is
+ * NULL, all kobjects are freed.
+ */
+static void klp_free_objects_limited(struct klp_patch *patch,
+				     struct klp_object *limit)
+{
+	struct klp_object *obj;
+
+	for (obj = patch->objs; obj->funcs && obj != limit; obj++) {
+		klp_free_funcs_limited(obj, NULL);
+		kobject_put(obj->kobj);
+	}
+}
+
+static void klp_free_patch(struct klp_patch *patch)
+{
+	klp_free_objects_limited(patch, NULL);
+	if (!list_empty(&patch->list))
+		list_del(&patch->list);
+	kobject_put(&patch->kobj);
+}
+
+static int klp_init_func(struct klp_object *obj, struct klp_func *func)
+{
+	struct ftrace_ops *ops;
+	int ret;
+
+	func->state = KLP_DISABLED;
+
+	ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+	if (!ops)
+		ret = -ENOMEM;
+
+	ops->private = func;
+	ops->func = klp_ftrace_handler;
+	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+	func->fops = ops;
+
+	ret = kobject_init_and_add(&func->kobj, &klp_ktype_func,
+				   obj->kobj, func->old_name);
+	if (ret) {
+		kfree(func->fops);
+		return ret;
+	}
+
+	return 0;
+}
+
+/* parts of the initialization that is done only when the object is loaded */
+static int klp_init_object_loaded(struct klp_patch *patch,
+				  struct klp_object *obj)
+{
+	struct klp_func *func;
+	int ret;
+
+	if (obj->relocs) {
+		ret = klp_write_object_relocations(patch->mod, obj);
+		if (ret)
+			return ret;
+	}
+
+	for (func = obj->funcs; func->old_name; func++) {
+		ret = klp_find_verify_func_addr(obj, func);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
+{
+	struct klp_func *func;
+	int ret;
+	const char *name;
+
+	if (!obj->funcs)
+		return -EINVAL;
+
+	obj->state = KLP_DISABLED;
+
+	klp_find_object_module(obj);
+
+	name = klp_is_module(obj) ? obj->name : "vmlinux";
+	obj->kobj = kobject_create_and_add(name, &patch->kobj);
+	if (!obj->kobj)
+		return -ENOMEM;
+
+	for (func = obj->funcs; func->old_name; func++) {
+		ret = klp_init_func(obj, func);
+		if (ret)
+			goto free;
+	}
+
+	if (klp_is_object_loaded(obj)) {
+		ret = klp_init_object_loaded(patch, obj);
+		if (ret)
+			goto free;
+	}
+
+	return 0;
+
+free:
+	klp_free_funcs_limited(obj, func);
+	return ret;
+}
+
+static int klp_init_patch(struct klp_patch *patch)
+{
+	struct klp_object *obj;
+	int ret;
+
+	if (!patch->objs)
+		return -EINVAL;
+
+	mutex_lock(&klp_mutex);
+
+	patch->state = KLP_DISABLED;
+
+	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
+				   klp_root_kobj, patch->mod->name);
+	if (ret)
+		goto unlock;
+
+	for (obj = patch->objs; obj->funcs; obj++) {
+		ret = klp_init_object(patch, obj);
+		if (ret)
+			goto free;
+	}
+
+	list_add(&patch->list, &klp_patches);
+
+	mutex_unlock(&klp_mutex);
+
+	return 0;
+
+free:
+	klp_free_objects_limited(patch, obj);
+	kobject_put(&patch->kobj);
+unlock:
+	mutex_unlock(&klp_mutex);
+	return ret;
+}
+
+/**
+ * klp_unregister_patch() - unregisters a patch
+ * @patch:	Disabled patch to be unregistered
+ *
+ * Frees the data structures and removes the sysfs interface.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_unregister_patch(struct klp_patch *patch)
+{
+	int ret = 0;
+
+	if (!klp_is_enabled())
+		return -ENODEV;
+
+	mutex_lock(&klp_mutex);
+
+	if (!klp_patch_is_registered(patch)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (patch->state == KLP_ENABLED) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	klp_free_patch(patch);
+
+out:
+	mutex_unlock(&klp_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(klp_unregister_patch);
+
+/**
+ * klp_register_patch() - registers a patch
+ * @patch:	Patch to be registered
+ *
+ * Initializes the data structure associated with the patch and
+ * creates the sysfs interface.
+ *
+ * Return: 0 on success, otherwise error
+ */
+int klp_register_patch(struct klp_patch *patch)
+{
+	int ret;
+
+	if (!klp_is_enabled())
+		return -ENODEV;
+
+	if (!patch || !patch->mod)
+		return -EINVAL;
+
+	/*
+	 * A reference is taken on the patch module to prevent it from being
+	 * unloaded.  Right now, we don't allow patch modules to unload since
+	 * there is currently no method to determine if a thread is still
+	 * running in the patched code contained in the patch module once
+	 * the ftrace registration is successful.
+	 */
+	if (!try_module_get(patch->mod))
+		return -ENODEV;
+
+	ret = klp_init_patch(patch);
+	if (ret)
+		module_put(patch->mod);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(klp_register_patch);
+
+static void klp_module_notify_coming(struct klp_patch *patch,
+				     struct klp_object *obj)
+{
+	struct module *pmod = patch->mod;
+	struct module *mod = obj->mod;
+	int ret;
+
+	pr_notice("applying patch '%s' to loading module '%s'\n",
+		  pmod->name, mod->name);
+
+	ret = klp_init_object_loaded(patch, obj);
+	if (ret)
+		goto err;
+
+	ret = klp_enable_object(obj);
+	if (!ret)
+		return;
+
+err:
+	pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
+		pmod->name, mod->name, ret);
+}
+
+static void klp_module_notify_going(struct klp_patch *patch,
+				    struct klp_object *obj)
+{
+	struct module *pmod = patch->mod;
+	struct module *mod = obj->mod;
+	int ret;
+
+	pr_notice("reverting patch '%s' on unloading module '%s'\n",
+		  pmod->name, mod->name);
+
+	ret = klp_disable_object(obj);
+	if (ret)
+		pr_warn("failed to revert patch '%s' on module '%s' (%d)\n",
+			pmod->name, mod->name, ret);
+
+	klp_free_object_loaded(obj);
+}
+
+static int klp_module_notify(struct notifier_block *nb, unsigned long action,
+			     void *data)
+{
+	struct module *mod = data;
+	struct klp_patch *patch;
+	struct klp_object *obj;
+
+	if (action != MODULE_STATE_COMING && action != MODULE_STATE_GOING)
+		return 0;
+
+	mutex_lock(&klp_mutex);
+
+	list_for_each_entry(patch, &klp_patches, list) {
+		if (patch->state == KLP_DISABLED)
+			continue;
+
+		for (obj = patch->objs; obj->funcs; obj++) {
+			if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
+				continue;
+
+			if (action == MODULE_STATE_COMING) {
+				obj->mod = mod;
+				klp_module_notify_coming(patch, obj);
+			} else /* MODULE_STATE_GOING */
+				klp_module_notify_going(patch, obj);
+
+			break;
+		}
+	}
+
+	mutex_unlock(&klp_mutex);
+
+	return 0;
+}
+
+static struct notifier_block klp_module_nb = {
+	.notifier_call = klp_module_notify,
+	.priority = INT_MIN+1, /* called late but before ftrace notifier */
+};
+
+static int klp_init(void)
+{
+	int ret;
+
+	ret = register_module_notifier(&klp_module_nb);
+	if (ret)
+		return ret;
+
+	klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
+	if (!klp_root_kobj) {
+		ret = -ENOMEM;
+		goto unregister;
+	}
+
+	return 0;
+
+unregister:
+	unregister_module_notifier(&klp_module_nb);
+	return ret;
+}
+
+module_init(klp_init);
-- 
2.1.0

[PATCHv6 3/3] samples: add sample live patching module

[Josh Poimboeuf]

From: Seth Jennings <sjenning@redhat.com>

Add a sample live patching module.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
---
 MAINTAINERS                          |  1 +
 samples/Kconfig                      |  7 +++
 samples/Makefile                     |  2 +-
 samples/livepatch/Makefile           |  1 +
 samples/livepatch/livepatch-sample.c | 87 ++++++++++++++++++++++++++++++++++++
 5 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100644 samples/livepatch/Makefile
 create mode 100644 samples/livepatch/livepatch-sample.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 94f9f69..15c0929d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5788,6 +5788,7 @@ F:	include/linux/livepatch.h
 F:	arch/x86/include/asm/livepatch.h
 F:	arch/x86/kernel/livepatch.c
 F:	Documentation/ABI/testing/sysfs-kernel-livepatch
+F:	samples/livepatch/
 L:	live-patching@vger.kernel.org
 
 LLC (802.2)
diff --git a/samples/Kconfig b/samples/Kconfig
index 6181c2c..0aed20d 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -63,4 +63,11 @@ config SAMPLE_RPMSG_CLIENT
 	  to communicate with an AMP-configured remote processor over
 	  the rpmsg bus.
 
+config SAMPLE_LIVE_PATCHING
+	tristate "Build live patching sample -- loadable modules only"
+	depends on LIVE_PATCHING && m
+	help
+	  Builds a sample live patch that replaces the procfs handler
+	  for /proc/cmdline to print "this has been live patched".
+
 endif # SAMPLES
diff --git a/samples/Makefile b/samples/Makefile
index 1a60c62..f00257b 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -1,4 +1,4 @@
 # Makefile for Linux samples code
 
-obj-$(CONFIG_SAMPLES)	+= kobject/ kprobes/ trace_events/ \
+obj-$(CONFIG_SAMPLES)	+= kobject/ kprobes/ trace_events/ livepatch/ \
 			   hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/
diff --git a/samples/livepatch/Makefile b/samples/livepatch/Makefile
new file mode 100644
index 0000000..7f1cdc1
--- /dev/null
+++ b/samples/livepatch/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SAMPLE_LIVE_PATCHING) += livepatch-sample.o
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
new file mode 100644
index 0000000..21f159d
--- /dev/null
+++ b/samples/livepatch/livepatch-sample.c
@@ -0,0 +1,87 @@
+/*
+ * livepatch-sample.c - Kernel Live Patching Sample Module
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/livepatch.h>
+
+/*
+ * This (dumb) live patch overrides the function that prints the
+ * kernel boot cmdline when /proc/cmdline is read.
+ *
+ * Example:
+ * $ cat /proc/cmdline
+ * <your cmdline>
+ * $ insmod livepatch-sample.ko
+ * $ cat /proc/cmdline
+ * this has been live patched
+ * $ echo 0 > /sys/kernel/livepatch/klp_sample/enabled
+ * <your cmdline>
+ */
+
+#include <linux/seq_file.h>
+static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%s\n", "this has been live patched");
+	return 0;
+}
+
+static struct klp_func funcs[] = {
+	{
+		.old_name = "cmdline_proc_show",
+		.new_func = livepatch_cmdline_proc_show,
+	}, { }
+};
+
+static struct klp_object objs[] = {
+	{
+		/* name being NULL means vmlinux */
+		.funcs = funcs,
+	}, { }
+};
+
+static struct klp_patch patch = {
+	.mod = THIS_MODULE,
+	.objs = objs,
+};
+
+static int livepatch_init(void)
+{
+	int ret;
+
+	ret = klp_register_patch(&patch);
+	if (ret)
+		return ret;
+	ret = klp_enable_patch(&patch);
+	if (ret) {
+		WARN_ON(klp_unregister_patch(&patch));
+		return ret;
+	}
+	return 0;
+}
+
+static void livepatch_exit(void)
+{
+	WARN_ON(klp_disable_patch(&patch));
+	WARN_ON(klp_unregister_patch(&patch));
+}
+
+module_init(livepatch_init);
+module_exit(livepatch_exit);
+MODULE_LICENSE("GPL");
-- 
2.1.0

Re: [PATCHv6 2/3] kernel: add support for live patching

[Miroslav Benes]

Hi, 

I think we are really close (or I hope so). I found few suspicious things 
or nitpicks though. They might have applied also to v5, but I didn't 
manage to look at that. Sorry about that.

On Wed, 10 Dec 2014, Josh Poimboeuf wrote:

> +/* klp_mutex must be held by caller */
> +static bool klp_patch_is_registered(struct klp_patch *patch)

Maybe klp_is_patch_registered is more appropriate name (consistent with 
other predicates in the file).

> +{
> +	struct klp_patch *mypatch;
> +
> +	list_for_each_entry(mypatch, &klp_patches, list)
> +		if (mypatch == patch)
> +			return true;
> +
> +	return false;
> +}

[...]

> +static int klp_disable_func(struct klp_func *func)
> +{
> +	int ret;
> +
> +	if (WARN_ON(func->state != KLP_ENABLED))
> +		return -EINVAL;
> +
> +	if (WARN_ON(!func->old_addr))
> +		return -EINVAL;
> +
> +	ret = unregister_ftrace_function(func->fops);
> +	if (ret) {
> +		pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
> +		       func->old_name, ret);
> +		return ret;
> +	}
> +
> +	ret = ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
> +	if (ret)
> +		pr_warn("function unregister succeeded but failed to clear the filter\n");
> +
> +	func->state = KLP_DISABLED;
> +
> +	return 0;
> +}
> +
> +static int klp_enable_func(struct klp_func *func)
> +{
> +	int ret;
> +
> +	if (WARN_ON(!func->old_addr))
> +		return -EINVAL;
> +
> +	if (WARN_ON(func->state != KLP_DISABLED))
> +		return -EINVAL;
> +
> +	ret = ftrace_set_filter_ip(func->fops, func->old_addr, 0, 0);
> +	if (ret) {
> +		pr_err("failed to set ftrace filter for function '%s' (%d)\n",
> +		       func->old_name, ret);
> +		return ret;
> +	}
> +
> +	ret = register_ftrace_function(func->fops);
> +	if (ret) {
> +		pr_err("failed to register ftrace handler for function '%s' (%d)\n",
> +		       func->old_name, ret);
> +		ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
> +	} else {
> +		func->state = KLP_ENABLED;
> +	}
> +
> +	return ret;
> +}

Just to be sure about our policy. We want to be stricter during enabling 
than in disabling process. Is that correct? Otherwise there is 
inconsistency in pr_* macros and return values. Also fops could be 
hypothetically registered back when ftrace_set_filter_ip fails in 
klp_disable_func. I just want to be sure that we didn't overlook 
anything...

[...]

> +static int klp_init_func(struct klp_object *obj, struct klp_func *func)
> +{
> +	struct ftrace_ops *ops;
> +	int ret;
> +
> +	func->state = KLP_DISABLED;
> +
> +	ops = kzalloc(sizeof(*ops), GFP_KERNEL);
> +	if (!ops)
> +		ret = -ENOMEM;

There should be return -ENOMEM.

> +
> +	ops->private = func;
> +	ops->func = klp_ftrace_handler;
> +	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
> +	func->fops = ops;
> +
> +	ret = kobject_init_and_add(&func->kobj, &klp_ktype_func,
> +				   obj->kobj, func->old_name);
> +	if (ret) {
> +		kfree(func->fops);
> +		return ret;
> +	}
> +
> +	return 0;
> +}

[...]

> +static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
> +{
> +	struct klp_func *func;
> +	int ret;
> +	const char *name;
> +
> +	if (!obj->funcs)
> +		return -EINVAL;
> +
> +	obj->state = KLP_DISABLED;
> +
> +	klp_find_object_module(obj);
> +
> +	name = klp_is_module(obj) ? obj->name : "vmlinux";
> +	obj->kobj = kobject_create_and_add(name, &patch->kobj);
> +	if (!obj->kobj)
> +		return -ENOMEM;
> +
> +	for (func = obj->funcs; func->old_name; func++) {
> +		ret = klp_init_func(obj, func);
> +		if (ret)
> +			goto free;
> +	}
> +
> +	if (klp_is_object_loaded(obj)) {
> +		ret = klp_init_object_loaded(patch, obj);
> +		if (ret)
> +			goto free;
> +	}
> +
> +	return 0;
> +
> +free:
> +	klp_free_funcs_limited(obj, func);
> +	return ret;
> +}

Shouldn't we call kobject_put(obj->kobj) in free branch? If I am not wrong 
it is not freed anywhere else. We free only already initialized functions 
and already initialized objects later in klp_init_patch, but not the 
kobject of the currently failing object.

> +static int klp_init_patch(struct klp_patch *patch)
> +{
> +	struct klp_object *obj;
> +	int ret;
> +
> +	if (!patch->objs)
> +		return -EINVAL;
> +
> +	mutex_lock(&klp_mutex);
> +
> +	patch->state = KLP_DISABLED;
> +
> +	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
> +				   klp_root_kobj, patch->mod->name);
> +	if (ret)
> +		goto unlock;
> +
> +	for (obj = patch->objs; obj->funcs; obj++) {
> +		ret = klp_init_object(patch, obj);
> +		if (ret)
> +			goto free;
> +	}
> +
> +	list_add(&patch->list, &klp_patches);
> +
> +	mutex_unlock(&klp_mutex);
> +
> +	return 0;
> +
> +free:
> +	klp_free_objects_limited(patch, obj);
> +	kobject_put(&patch->kobj);
> +unlock:
> +	mutex_unlock(&klp_mutex);
> +	return ret;
> +}

And that is everything. I like it, it has improved a lot. I hope that 
there are no other problems. I am getting blind looking at it all the 
time :)

Thank you
Mira

Re: [PATCHv6 2/3] kernel: add support for live patching

[Josh Poimboeuf]

On Fri, Dec 12, 2014 at 05:58:19PM +0100, Miroslav Benes wrote:
> 
> Hi, 
> 
> I think we are really close (or I hope so). I found few suspicious things 
> or nitpicks though. They might have applied also to v5, but I didn't 
> manage to look at that. Sorry about that.
> 
> On Wed, 10 Dec 2014, Josh Poimboeuf wrote:
> 
> > +/* klp_mutex must be held by caller */
> > +static bool klp_patch_is_registered(struct klp_patch *patch)
> 
> Maybe klp_is_patch_registered is more appropriate name (consistent with 
> other predicates in the file).

Ok.

> > +static int klp_disable_func(struct klp_func *func)
> > +{
> > +	int ret;
> > +
> > +	if (WARN_ON(func->state != KLP_ENABLED))
> > +		return -EINVAL;
> > +
> > +	if (WARN_ON(!func->old_addr))
> > +		return -EINVAL;
> > +
> > +	ret = unregister_ftrace_function(func->fops);
> > +	if (ret) {
> > +		pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
> > +		       func->old_name, ret);
> > +		return ret;
> > +	}
> > +
> > +	ret = ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
> > +	if (ret)
> > +		pr_warn("function unregister succeeded but failed to clear the filter\n");
> > +
> > +	func->state = KLP_DISABLED;
> > +
> > +	return 0;
> > +}
> > +
> > +static int klp_enable_func(struct klp_func *func)
> > +{
> > +	int ret;
> > +
> > +	if (WARN_ON(!func->old_addr))
> > +		return -EINVAL;
> > +
> > +	if (WARN_ON(func->state != KLP_DISABLED))
> > +		return -EINVAL;
> > +
> > +	ret = ftrace_set_filter_ip(func->fops, func->old_addr, 0, 0);
> > +	if (ret) {
> > +		pr_err("failed to set ftrace filter for function '%s' (%d)\n",
> > +		       func->old_name, ret);
> > +		return ret;
> > +	}
> > +
> > +	ret = register_ftrace_function(func->fops);
> > +	if (ret) {
> > +		pr_err("failed to register ftrace handler for function '%s' (%d)\n",
> > +		       func->old_name, ret);
> > +		ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
> > +	} else {
> > +		func->state = KLP_ENABLED;
> > +	}
> > +
> > +	return ret;
> > +}
> 
> Just to be sure about our policy. We want to be stricter during enabling 
> than in disabling process. Is that correct? Otherwise there is 
> inconsistency in pr_* macros and return values. Also fops could be 
> hypothetically registered back when ftrace_set_filter_ip fails in 
> klp_disable_func. I just want to be sure that we didn't overlook 
> anything...

The asymmetry in the enable/disable error handling is intentional.  In
klp_disable_func(), a ftrace_set_filter_ip() failure isn't a fatal
condition because we've already unregistered the fops and thus removed
the patch.

> > +static int klp_init_func(struct klp_object *obj, struct klp_func *func)
> > +{
> > +	struct ftrace_ops *ops;
> > +	int ret;
> > +
> > +	func->state = KLP_DISABLED;
> > +
> > +	ops = kzalloc(sizeof(*ops), GFP_KERNEL);
> > +	if (!ops)
> > +		ret = -ENOMEM;
> 
> There should be return -ENOMEM.

Agreed.

> > +static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
> > +{
> > +	struct klp_func *func;
> > +	int ret;
> > +	const char *name;
> > +
> > +	if (!obj->funcs)
> > +		return -EINVAL;
> > +
> > +	obj->state = KLP_DISABLED;
> > +
> > +	klp_find_object_module(obj);
> > +
> > +	name = klp_is_module(obj) ? obj->name : "vmlinux";
> > +	obj->kobj = kobject_create_and_add(name, &patch->kobj);
> > +	if (!obj->kobj)
> > +		return -ENOMEM;
> > +
> > +	for (func = obj->funcs; func->old_name; func++) {
> > +		ret = klp_init_func(obj, func);
> > +		if (ret)
> > +			goto free;
> > +	}
> > +
> > +	if (klp_is_object_loaded(obj)) {
> > +		ret = klp_init_object_loaded(patch, obj);
> > +		if (ret)
> > +			goto free;
> > +	}
> > +
> > +	return 0;
> > +
> > +free:
> > +	klp_free_funcs_limited(obj, func);
> > +	return ret;
> > +}
> 
> Shouldn't we call kobject_put(obj->kobj) in free branch? If I am not wrong 
> it is not freed anywhere else. We free only already initialized functions 
> and already initialized objects later in klp_init_patch, but not the 
> kobject of the currently failing object.

Agreed.

> And that is everything. I like it, it has improved a lot. I hope that 
> there are no other problems. I am getting blind looking at it all the 
> time :)

Thanks!  I'll send out the next patch set soon, maybe Monday.

-- 
Josh