[PATCHv3 2/3] kernel: add support for live patching

[Seth Jennings]

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@xxxxxxxxxx>
---
 MAINTAINERS                      |  12 +
 arch/x86/Kconfig                 |   3 +
 arch/x86/include/asm/livepatch.h |  37 ++
 arch/x86/kernel/Makefile         |   1 +
 arch/x86/kernel/livepatch.c      |  74 ++++
 include/linux/livepatch.h        |  96 +++++
 kernel/Makefile                  |   1 +
 kernel/livepatch/Kconfig         |  18 +
 kernel/livepatch/Makefile        |   3 +
 kernel/livepatch/core.c          | 828 +++++++++++++++++++++++++++++++++++++++
 10 files changed, 1073 insertions(+)
 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/MAINTAINERS b/MAINTAINERS
index 4861577..c7f49ae 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5715,6 +5715,18 @@ F:	Documentation/misc-devices/lis3lv02d
 F:	drivers/misc/lis3lv02d/
 F:	drivers/platform/x86/hp_accel.c
 
+LIVE PATCHING
+M:	Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
+M:	Seth Jennings <sjenning@xxxxxxxxxx>
+M:	Jiri Kosina <jkosina@xxxxxxx>
+M:	Vojtech Pavlik <vojtech@xxxxxxx>
+S:	Maintained
+F:	kernel/livepatch/
+F:	include/linux/livepatch.h
+F:	arch/x86/include/asm/livepatch.h
+F:	arch/x86/kernel/livepatch.c
+L:	live-patching@xxxxxxxxxxxxxxx
+
 LLC (802.2)
 M:	Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxxxxxxx>
 S:	Maintained
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ec21dfd..78715fd 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
@@ -1991,6 +1992,8 @@ 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..2ed86ec
--- /dev/null
+++ b/arch/x86/include/asm/livepatch.h
@@ -0,0 +1,37 @@
+/*
+ * livepatch.h - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
+ *
+ * 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
+extern int klp_write_module_reloc(struct module *mod, unsigned long type,
+				  unsigned long loc, unsigned long value);
+
+#else
+static int klp_write_module_reloc(struct module *mod, unsigned long type,
+				  unsigned long loc, unsigned long value)
+{
+	return -ENOSYS;
+}
+#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..777a4a4
--- /dev/null
+++ b/arch/x86/kernel/livepatch.c
@@ -0,0 +1,74 @@
+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
+ *
+ * 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>
+
+int klp_write_module_reloc(struct module *mod, unsigned long type,
+			   unsigned long loc, unsigned long value)
+{
+	int ret, readonly, numpages, size = 4;
+	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_ro_size)
+		readonly = 1;
+	else if (loc >= core + core_ro_size && loc < core + core_size)
+		readonly = 0;
+	else
+		/* loc not in expected range */
+		return -EINVAL;
+
+	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..eab84df
--- /dev/null
+++ b/include/linux/livepatch.h
@@ -0,0 +1,96 @@
+/*
+ * livepatch.h - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
+ *
+ * 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>
+
+/* TODO: add kernel-doc for structures once agreed upon */
+
+enum klp_state {
+	LPC_DISABLED,
+	LPC_ENABLED
+};
+
+struct klp_func {
+	/* external */
+	const char *old_name; /* function to be patched */
+	void *new_func; /* replacement function in patch module */
+	/*
+	 * 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 {
+	unsigned long dest;
+	unsigned long src;
+	unsigned long type;
+	const char *name;
+	int addend;
+	int external;
+};
+
+struct klp_object {
+	/* external */
+	const char *name; /* "vmlinux" or module name */
+	struct klp_reloc *relocs;
+	struct klp_func *funcs;
+
+	/* internal */
+	struct kobject *kobj;
+	struct module *mod; /* module associated with object */
+	enum klp_state state;
+};
+
+struct klp_patch {
+	/* external */
+	struct module *mod; /* module containing the patch */
+	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..9140e42
--- /dev/null
+++ b/kernel/livepatch/core.c
@@ -0,0 +1,828 @@
+/*
+ * core.c - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
+ *
+ * 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>
+
+/*************************************
+ * Core structures
+ ************************************/
+
+static DEFINE_MUTEX(klp_mutex);
+static LIST_HEAD(klp_patches);
+
+/*******************************************
+ * Helpers
+ *******************************************/
+
+/* sets obj->mod if object is not vmlinux and module is found */
+static bool klp_find_object_module(struct klp_object *obj)
+{
+	if (!strcmp(obj->name, "vmlinux"))
+		return 1;
+
+	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);
+
+	return !!obj->mod;
+}
+
+/************************************
+ * kallsyms
+ ***********************************/
+
+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_symbol() handles this and only returns the
+	 * addr if count == 1.
+	 */
+	args->addr = addr;
+	args->count++;
+
+	return 0;
+}
+
+static int klp_find_symbol(const char *objname, const char *name,
+			   unsigned long *addr)
+{
+	struct klp_find_arg args = {
+		.objname = objname,
+		.name = name,
+		.addr = 0,
+		.count = 0
+	};
+
+	if (objname && !strcmp(objname, "vmlinux"))
+		args.objname = NULL;
+
+	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_func *func, const char *objname)
+{
+	int ret;
+
+#if defined(CONFIG_RANDOMIZE_BASE)
+	/* KASLR is enabled, disregard old_addr from user */
+	func->old_addr = 0;
+#endif
+
+	if (func->old_addr && strcmp(objname, "vmlinux")) {
+		pr_err("old address specified for module symbol\n");
+		return -EINVAL;
+	}
+
+	if (func->old_addr)
+		ret = klp_verify_vmlinux_symbol(func->old_name,
+						func->old_addr);
+	else
+		ret = klp_find_symbol(objname, func->old_name,
+				      &func->old_addr);
+
+	return ret;
+}
+
+/****************************************
+ * dynamic relocations (load-time linker)
+ ****************************************/
+
+/*
+ * 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_symbol(pmod->name, name, addr);
+}
+
+static int klp_write_object_relocations(struct module *pmod,
+					struct klp_object *obj)
+{
+	int ret;
+	struct klp_reloc *reloc;
+
+	for (reloc = obj->relocs; reloc->name; reloc++) {
+		if (!strcmp(obj->name, "vmlinux")) {
+			ret = klp_verify_vmlinux_symbol(reloc->name,
+							reloc->src);
+			if (ret)
+				return ret;
+		} else {
+			/* module, reloc->src needs to be discovered */
+			if (reloc->external)
+				ret = klp_find_external_symbol(pmod,
+							       reloc->name,
+							       &reloc->src);
+			else
+				ret = klp_find_symbol(obj->mod->name,
+						      reloc->name,
+						      &reloc->src);
+			if (ret)
+				return ret;
+		}
+		ret = klp_write_module_reloc(pmod, reloc->type, reloc->dest,
+					     reloc->src + reloc->addend);
+		if (ret) {
+			pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
+			       reloc->name, reloc->src, ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+/***********************************
+ * ftrace registration
+ **********************************/
+
+static void 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_enable_func(struct klp_func *func)
+{
+	int ret;
+
+	if (WARN_ON(!func->old_addr || func->state != LPC_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 = LPC_ENABLED;
+
+	return ret;
+}
+
+static int klp_disable_func(struct klp_func *func)
+{
+	int ret;
+
+	if (WARN_ON(func->state != LPC_ENABLED))
+		return -EINVAL;
+
+	if (!func->old_addr)
+		/* parent object is not loaded */
+		return 0;
+	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 = LPC_DISABLED;
+
+	return 0;
+}
+
+static int klp_disable_object(struct klp_object *obj)
+{
+	struct klp_func *func;
+	int ret;
+
+	for (func = obj->funcs; func->old_name; func++) {
+		if (func->state != LPC_ENABLED)
+			continue;
+		ret = klp_disable_func(func);
+		if (ret)
+			return ret;
+		if (strcmp(obj->name, "vmlinux"))
+			func->old_addr = 0;
+	}
+	obj->state = LPC_DISABLED;
+
+	return 0;
+}
+
+static int klp_enable_object(struct module *pmod, struct klp_object *obj)
+{
+	struct klp_func *func;
+	int ret;
+
+	if (WARN_ON(!obj->mod && strcmp(obj->name, "vmlinux")))
+		return -EINVAL;
+
+	if (obj->relocs) {
+		ret = klp_write_object_relocations(pmod, obj);
+		if (ret)
+			goto unregister;
+	}
+
+	for (func = obj->funcs; func->old_name; func++) {
+		ret = klp_find_verify_func_addr(func, obj->name);
+		if (ret)
+			goto unregister;
+
+		ret = klp_enable_func(func);
+		if (ret)
+			goto unregister;
+	}
+	obj->state = LPC_ENABLED;
+
+	return 0;
+unregister:
+	WARN_ON(klp_disable_object(obj));
+	return ret;
+}
+
+/******************************
+ * enable/disable
+ ******************************/
+
+static int __klp_disable_patch(struct klp_patch *patch)
+{
+	struct klp_object *obj;
+	int ret;
+
+	pr_notice("disabling patch '%s'\n", patch->mod->name);
+
+	for (obj = patch->objs; obj->name; obj++) {
+		if (obj->state != LPC_ENABLED)
+			continue;
+		ret = klp_disable_object(obj);
+		if (ret)
+			return ret;
+	}
+	patch->state = LPC_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;
+
+	mutex_lock(&klp_mutex);
+	ret = __klp_disable_patch(patch);
+	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 != LPC_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->name; obj++) {
+		if (!klp_find_object_module(obj))
+			continue;
+		ret = klp_enable_object(patch->mod, obj);
+		if (ret)
+			goto unregister;
+	}
+	patch->state = LPC_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;
+
+	mutex_lock(&klp_mutex);
+	ret = __klp_enable_patch(patch);
+	mutex_unlock(&klp_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(klp_enable_patch);
+
+/******************************
+ * module notifier
+ *****************************/
+
+static void klp_module_notify_coming(struct module *pmod,
+				     struct klp_object *obj)
+{
+	struct module *mod = obj->mod;
+	int ret;
+
+	pr_notice("applying patch '%s' to loading module '%s'\n",
+		  pmod->name, mod->name);
+	obj->mod = mod;
+	ret = klp_enable_object(pmod, obj);
+	if (ret)
+		pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
+			pmod->name, mod->name, ret);
+}
+
+static void klp_module_notify_going(struct module *pmod,
+				    struct klp_object *obj)
+{
+	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);
+	obj->mod = NULL;
+}
+
+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 == LPC_DISABLED)
+			continue;
+		for (obj = patch->objs; obj->name; obj++) {
+			if (strcmp(obj->name, mod->name))
+				continue;
+			if (action == MODULE_STATE_COMING) {
+				obj->mod = mod;
+				klp_module_notify_coming(patch->mod, obj);
+			} else /* MODULE_STATE_GOING */
+				klp_module_notify_going(patch->mod, 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 */
+};
+
+/********************************************
+ * 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 != LPC_DISABLED && val != LPC_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 == LPC_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 struct kobject *klp_root_kobj;
+
+static int klp_create_root_kobj(void)
+{
+	klp_root_kobj =
+		kobject_create_and_add("livepatch", kernel_kobj);
+	if (!klp_root_kobj)
+		return -ENOMEM;
+	return 0;
+}
+
+static void klp_remove_root_kobj(void)
+{
+	kobject_put(klp_root_kobj);
+}
+
+static void klp_kobj_release_patch(struct kobject *kobj)
+{
+	struct klp_patch *patch;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+	if (!list_empty(&patch->list))
+		list_del(&patch->list);
+}
+
+static struct kobj_type klp_ktype_patch = {
+	.release = klp_kobj_release_patch,
+	.sysfs_ops = &kobj_sysfs_ops,
+	.default_attrs = klp_patch_attrs
+};
+
+/*********************************
+ * structure allocation
+ ********************************/
+
+/*
+ * 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);
+}
+
+/*
+ * 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->name && 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);
+	kobject_put(&patch->kobj);
+}
+
+static int klp_init_funcs(struct klp_object *obj)
+{
+	struct klp_func *func;
+	struct ftrace_ops *ops;
+
+	for (func = obj->funcs; func->old_name; func++) {
+		func->state = LPC_DISABLED;
+		ops = &func->fops;
+		ops->private = func;
+		ops->func = klp_ftrace_handler;
+		ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+
+		/* sysfs */
+		func->kobj = kobject_create_and_add(func->old_name, obj->kobj);
+		if (!func->kobj)
+			goto free;
+	}
+
+	return 0;
+free:
+	klp_free_funcs_limited(obj, func);
+	return -ENOMEM;
+}
+
+static int klp_init_objects(struct klp_patch *patch)
+{
+	struct klp_object *obj;
+	int ret;
+
+	for (obj = patch->objs; obj->name; obj++) {
+		/* obj->mod set by klp_object_module_get() */
+		obj->state = LPC_DISABLED;
+
+		/* sysfs */
+		obj->kobj = kobject_create_and_add(obj->name, &patch->kobj);
+		if (!obj->kobj)
+			goto free;
+
+		/* init functions */
+		ret = klp_init_funcs(obj);
+		if (ret) {
+			kobject_put(obj->kobj);
+			goto free;
+		}
+	}
+
+	return 0;
+free:
+	klp_free_objects_limited(patch, obj);
+	return -ENOMEM;
+}
+
+static int klp_init_patch(struct klp_patch *patch)
+{
+	int ret;
+
+	mutex_lock(&klp_mutex);
+
+	/* init */
+	patch->state = LPC_DISABLED;
+
+	/* sysfs */
+	ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
+				   klp_root_kobj, patch->mod->name);
+	if (ret)
+		return ret;
+
+	/* create objects */
+	ret = klp_init_objects(patch);
+	if (ret) {
+		kobject_put(&patch->kobj);
+		return ret;
+	}
+
+	/* add to global list of patches */
+	list_add(&patch->list, &klp_patches);
+
+	mutex_unlock(&klp_mutex);
+
+	return 0;
+}
+
+/************************************
+ * register/unregister
+ ***********************************/
+
+/**
+ * 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 (!patch || !patch->mod || !patch->objs)
+		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);
+
+/**
+ * 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;
+
+	mutex_lock(&klp_mutex);
+	if (patch->state == LPC_ENABLED) {
+		ret = -EINVAL;
+		goto out;
+	}
+	klp_free_patch(patch);
+out:
+	mutex_unlock(&klp_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(klp_unregister_patch);
+
+/************************************
+ * entry/exit
+ ************************************/
+
+static int klp_init(void)
+{
+	int ret;
+
+	ret = register_module_notifier(&klp_module_nb);
+	if (ret)
+		return ret;
+
+	ret = klp_create_root_kobj();
+	if (ret)
+		goto unregister;
+
+	return 0;
+unregister:
+	unregister_module_notifier(&klp_module_nb);
+	return ret;
+}
+
+static void klp_exit(void)
+{
+	klp_remove_root_kobj();
+	unregister_module_notifier(&klp_module_nb);
+}
+
+module_init(klp_init);
+module_exit(klp_exit);
+MODULE_DESCRIPTION("Live Kernel Patching Core");
+MODULE_LICENSE("GPL");
-- 
1.9.3

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