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

Pull live patching infrastructure from Jiri Kosina:
 "Let me provide a bit of history first, before describing what is in
  this pile.

  Originally, there was kSplice as a standalone project that implemented
  stop_machine()-based patching for the linux kernel.  This project got
  later acquired, and the current owner is providing live patching as a
  proprietary service, without any intentions to have their
  implementation merged.

  Then, due to rising user/customer demand, both Red Hat and SUSE
  started working on their own implementation (not knowing about each
  other), and announced first versions roughly at the same time [1] [2].

  The principle difference between the two solutions is how they are
  making sure that the patching is performed in a consistent way when it
  comes to different execution threads with respect to the semantic
  nature of the change that is being introduced.

  In a nutshell, kPatch is issuing stop_machine(), then looking at
  stacks of all existing processess, and if it decides that the system
  is in a state that can be patched safely, it proceeds insterting code
  redirection machinery to the patched functions.

  On the other hand, kGraft provides a per-thread consistency during one
  single pass of a process through the kernel and performs a lazy
  contignuous migration of threads from "unpatched" universe to the
  "patched" one at safe checkpoints.

  If interested in a more detailed discussion about the consistency
  models and its possible combinations, please see the thread that
  evolved around [3].

  It pretty quickly became obvious to the interested parties that it's
  absolutely impractical in this case to have several isolated solutions
  for one task to co-exist in the kernel.  During a dedicated Live
  Kernel Patching track at LPC in Dusseldorf, all the interested parties
  sat together and came up with a joint aproach that would work for both
  distro vendors.  Steven Rostedt took notes [4] from this meeting.

  And the foundation for that aproach is what's present in this pull
  request.

  It provides a basic infrastructure for function "live patching" (i.e.
  code redirection), including API for kernel modules containing the
  actual patches, and API/ABI for userspace to be able to operate on the
  patches (look up what patches are applied, enable/disable them, etc).

  It's relatively simple and minimalistic, as it's making use of
  existing kernel infrastructure (namely ftrace) as much as possible.
  It's also self-contained, in a sense that it doesn't hook itself in
  any other kernel subsystem (it doesn't even touch any other code).
  It's now implemented for x86 only as a reference architecture, but
  support for powerpc, s390 and arm is already in the works (adding
  arch-specific support basically boils down to teaching ftrace about
  regs-saving).

  Once this common infrastructure gets merged, both Red Hat and SUSE
  have agreed to immediately start porting their current solutions on
  top of this, abandoning their out-of-tree code.  The plan basically is
  that each patch will be marked by flag(s) that would indicate which
  consistency model it is willing to use (again, the details have been
  sketched out already in the thread at [3]).

  Before this happens, the current codebase can be used to patch a large
  group of secruity/stability problems the patches for which are not too
  complex (in a sense that they don't introduce non-trivial change of
  function's return value semantics, they don't change layout of data
  structures, etc) -- this corresponds to LEAVE_FUNCTION &&
  SWITCH_FUNCTION semantics described at [3].

  This tree has been in linux-next since December.

    [1] https://lkml.org/lkml/2014/4/30/477
    [2] https://lkml.org/lkml/2014/7/14/857
    [3] https://lkml.org/lkml/2014/11/7/354
    [4] http://linuxplumbersconf.org/2014/wp-content/uploads/2014/10/LPC2014_LivePatching.txt

  [ The core code is introduced by the three commits authored by Seth
    Jennings, which got a lot of changes incorporated during numerous
    respins and reviews of the initial implementation.  All the followup
    commits have materialized only after public tree has been created,
    so they were not folded into initial three commits so that the
    public tree doesn't get rebased ]"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: add missing newline to error message
  livepatch: rename config to CONFIG_LIVEPATCH
  livepatch: fix uninitialized return value
  livepatch: support for repatching a function
  livepatch: enforce patch stacking semantics
  livepatch: change ARCH_HAVE_LIVE_PATCHING to HAVE_LIVE_PATCHING
  livepatch: fix deferred module patching order
  livepatch: handle ancient compilers with more grace
  livepatch: kconfig: use bool instead of boolean
  livepatch: samples: fix usage example comments
  livepatch: MAINTAINERS: add git tree location
  livepatch: use FTRACE_OPS_FL_IPMODIFY
  livepatch: move x86 specific ftrace handler code to arch/x86
  livepatch: samples: add sample live patching module
  livepatch: kernel: add support for live patching
  livepatch: kernel: add TAINT_LIVEPATCH

Documentation/ABI/testing/sysfs-kernel-livepatch

+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.

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

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.
 
 ==============================================================
 

MAINTAINERS

@@ -5853,6 +5853,21 @@ 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
+F:	samples/livepatch/
+L:	live-patching@vger.kernel.org
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching.git
+
 LLC (802.2)
 M:	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
 S:	Maintained

arch/x86/Kconfig

@@ -17,6 +17,7 @@ config X86_64
 	depends on 64BIT
 	select X86_DEV_DMA_OPS
 	select ARCH_USE_CMPXCHG_LOCKREF
+	select HAVE_LIVEPATCH
 
 ### Arch settings
 config X86
@@ -2028,6 +2029,8 @@ 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

arch/x86/include/asm/livepatch.h

+/*
+ * livepatch.h - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * 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>
+#include <linux/ftrace.h>
+
+#ifdef CONFIG_LIVEPATCH
+static inline int klp_check_compiler_support(void)
+{
+#ifndef CC_USING_FENTRY
+	return 1;
+#endif
+	return 0;
+}
+extern 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)
+{
+	regs->ip = ip;
+}
+#else
+#error Live patching support is disabled; check CONFIG_LIVEPATCH
+#endif
+
+#endif /* _ASM_X86_LIVEPATCH_H */

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_LIVEPATCH)		+= livepatch.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
 obj-$(CONFIG_X86_TSC)		+= trace_clock.o

arch/x86/kernel/livepatch.c

+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * 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;
+}

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)]

include/linux/livepatch.h

+/*
+ * livepatch.h - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * 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_LIVEPATCH)
+
+#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
+ * @state:	tracks function-level patch application state
+ * @stack_node:	list node for klp_ops func_stack list
+ */
+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;
+	enum klp_state state;
+	struct list_head stack_node;
+};
+
+/**
+ * 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_LIVEPATCH */
+
+#endif /* _LINUX_LIVEPATCH_H_ */

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

kernel/livepatch/Kconfig

+config HAVE_LIVEPATCH
+	bool
+	help
+	  Arch supports kernel live patching
+
+config LIVEPATCH
+	bool "Kernel Live Patching"
+	depends on DYNAMIC_FTRACE_WITH_REGS
+	depends on MODULES
+	depends on SYSFS
+	depends on KALLSYMS_ALL
+	depends on HAVE_LIVEPATCH
+	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.

kernel/livepatch/Makefile

+obj-$(CONFIG_LIVEPATCH) += livepatch.o
+
+livepatch-objs := core.o

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().
  */

samples/Kconfig

@@ -63,4 +63,11 @@ config SAMPLE_RPMSG_CLIENT
 	  to communicate with an AMP-configured remote processor over
 	  the rpmsg bus.
 
+config SAMPLE_LIVEPATCH
+	tristate "Build live patching sample -- loadable modules only"
+	depends on LIVEPATCH && m
+	help
+	  Builds a sample live patch that replaces the procfs handler
+	  for /proc/cmdline to print "this has been live patched".
+
 endif # SAMPLES

samples/Makefile

 # 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/

samples/livepatch/Makefile

+obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-sample.o

samples/livepatch/livepatch-sample.c

+/*
+ * 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/livepatch_sample/enabled
+ * $ cat /proc/cmdline
+ * <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");