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livepatch: kernel: add support for live patching
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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.

[ jkosina@suse.cz: due to the number of contributions that got folded into
  this original patch from Seth Jennings, add SUSE's copyright as well, as
  discussed via e-mail ]

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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sjenning authored and Jiri Kosina committed Dec 22, 2014
1 parent c5f4546 commit b700e7f
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44 changes: 44 additions & 0 deletions Documentation/ABI/testing/sysfs-kernel-livepatch
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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.
13 changes: 13 additions & 0 deletions MAINTAINERS
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Expand Up @@ -5784,6 +5784,19 @@ 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
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3 changes: 3 additions & 0 deletions arch/x86/Kconfig
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Expand Up @@ -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
Expand Down Expand Up @@ -2008,6 +2009,8 @@ 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
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37 changes: 37 additions & 0 deletions arch/x86/include/asm/livepatch.h
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/*
* 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>

#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 */
1 change: 1 addition & 0 deletions arch/x86/kernel/Makefile
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Expand Up @@ -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
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90 changes: 90 additions & 0 deletions arch/x86/kernel/livepatch.c
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/*
* 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;
}
133 changes: 133 additions & 0 deletions include/linux/livepatch.h
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/*
* 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_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_ */
1 change: 1 addition & 0 deletions kernel/Makefile
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Expand Up @@ -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
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18 changes: 18 additions & 0 deletions kernel/livepatch/Kconfig
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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.
3 changes: 3 additions & 0 deletions kernel/livepatch/Makefile
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obj-$(CONFIG_LIVE_PATCHING) += livepatch.o

livepatch-objs := core.o
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