Kernel Live Patching

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 <[email protected]>

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 <[email protected]>

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 <[email protected]>

---
 Documentation/oops-tracing.txt  | 2 ++
 Documentation/sysctl/kernel.txt | 1 +
 include/linux/kernel.h          | 1 +
 kernel/panic.c                  | 2 ++
 4 files changed, 6 insertions(+)

Documentation/oops-tracing.txt +2 -0

index beefb9f..f3ac05c 100644
@@ -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 +1 -0

index 75511ef..83ab256 100644
@@ -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.
 
 ==============================================================
 

include/linux/kernel.h +1 -0

index 5449d2f..d03e3de 100644
@@ -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)]

kernel/panic.c +2 -0

index 4d8d6f9..8136ad7 100644
@@ -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().
  */

Quoted 4 lines

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.

Quoted 4 lines

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 <[email protected]>

Looks good to me.

Reviewed-by Masami Hiramatsu <[email protected]>

Quoted 9 lines · Masami Hiramatsu

Quoted 8 lines

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 <[email protected]>

Quoted 3 lines

Looks good to me.

Reviewed-by Masami Hiramatsu <[email protected]>

Masami, just for completness -- is this just for 1/3, or for the whole series? (so that I get it right once I am applying the patches to git tree).

Thanks,

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 <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

arch/x86/Kconfig +3 -0

index ce8dcdf..5c57181 100644
@@ -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

arch/x86/include/asm/livepatch.h new file +36 -0

new file mode 100644
index 0000000..c2ae592
@@ -0,0 +1,36 @@
+/*
+ * livepatch.h - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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 */

arch/x86/kernel/Makefile +1 -0

index 5d4502c..316b34e 100644
@@ -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

arch/x86/kernel/livepatch.c new file +25 -0

new file mode 100644
index 0000000..4b0ed7b
@@ -0,0 +1,89 @@
+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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>

arch/x86/kernel/livepatch.c new file +54 -0

+ */
+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/livepatch.h new file +132 -0

new file mode 100644
index 0000000..b61fe74
@@ -0,0 +1,132 @@
+/*
+ * livepatch.h - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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_ */

kernel/Makefile +1 -0

index a59481a..616994f 100644
@@ -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 new file +18 -0

new file mode 100644
index 0000000..96da00f
@@ -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.

kernel/livepatch/Makefile new file +3 -0

new file mode 100644
index 0000000..7c1f008
@@ -0,0 +1,3 @@
+obj-$(CONFIG_LIVE_PATCHING) += livepatch.o
+
+livepatch-objs := core.o

kernel/livepatch/core.c new file +213 -0

new file mode 100644
index 0000000..0004a71
@@ -0,0 +1,929 @@
+/*
+ * core.c - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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_is_patch_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_initialized(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);

kernel/livepatch/core.c new file +23 -0

+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,

kernel/livepatch/core.c new file +663 -0

+               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;
+
+       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;
+
+       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;
+
+       mutex_lock(&klp_mutex);
+
+       if (!klp_is_patch_registered(patch)) {
+               ret = -EINVAL;
+               goto err;
+       }
+
+       if (patch->state == KLP_DISABLED) {
+               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;
+
+       mutex_lock(&klp_mutex);
+
+       if (!klp_is_patch_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;
+
+       ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+       if (!ops)
+               return -ENOMEM;
+
+       ops->private = func;
+       ops->func = klp_ftrace_handler;
+       ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+       func->fops = ops;
+       func->state = KLP_DISABLED;
+
+       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);
+       kobject_put(obj->kobj);
+       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;
+
+       mutex_lock(&klp_mutex);
+
+       if (!klp_is_patch_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_initialized())
+               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;
+
+       ret = klp_init_object_loaded(patch, obj);
+       if (ret)
+               goto err;
+
+       if (patch->state == KLP_DISABLED)
+               return;
+
+       pr_notice("applying patch '%s' to loading module '%s'\n",
+                 pmod->name, mod->name);
+
+       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;
+
+       if (patch->state == KLP_DISABLED)
+               goto disabled;
+
+       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);
+
+disabled:
+       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) {
+               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;

Quoted 16 lines · 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 <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

snip

Quoted 110 lines

arch/x86/Kconfig +3 -0

index ce8dcdf..5c57181 100644
@@ -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

arch/x86/include/asm/livepatch.h new file +36 -0

new file mode 100644
index 0000000..c2ae592
@@ -0,0 +1,36 @@
+/*
+ * livepatch.h - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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 */

arch/x86/kernel/Makefile +1 -0

index 5d4502c..316b34e 100644
@@ -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

arch/x86/kernel/livepatch.c new file +29 -0

new file mode 100644
index 0000000..4b0ed7b
@@ -0,0 +1,89 @@
+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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

arch/x86/kernel/livepatch.c line 35

Quoted 6 lines

arch/x86/kernel/livepatch.c new file +6 -0

+ * @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.

This is more of the what then why?

Quoted 463 lines

arch/x86/kernel/livepatch.c new file +54 -0

+ */
+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/livepatch.h new file +132 -0

new file mode 100644
index 0000000..b61fe74
@@ -0,0 +1,132 @@
+/*
+ * livepatch.h - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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_ */

kernel/Makefile +1 -0

index a59481a..616994f 100644
@@ -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 new file +18 -0

new file mode 100644
index 0000000..96da00f
@@ -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.

kernel/livepatch/Makefile new file +3 -0

new file mode 100644
index 0000000..7c1f008
@@ -0,0 +1,3 @@
+obj-$(CONFIG_LIVE_PATCHING) += livepatch.o
+
+livepatch-objs := core.o

kernel/livepatch/core.c new file +219 -0

new file mode 100644
index 0000000..0004a71
@@ -0,0 +1,929 @@
+/*
+ * core.c - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <[email protected]>
+ *
+ * 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_is_patch_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_initialized(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;
+       }
+

kernel/livepatch/core.c line 223

Quoted 4 lines

kernel/livepatch/core.c new file +4 -0

+       /* otherwise check if it's in another .o within the patch module */
+       return klp_find_object_symbol(pmod->name, name, addr);
+}
+

Shouldn't the code above be asbtracted out for anyone searching for kernel symbols? Its only KLP at the moment, but I am sure these are reusable bits

Quoted 29 lines

kernel/livepatch/core.c new file +28 -0

+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);

kernel/livepatch/core.c line 256

Quoted 5 lines

kernel/livepatch/core.c new file +5 -0

+                       if (ret)
+                               return ret;
+               }
+               ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
+                                            reloc->val + reloc->addend);

An iterative loop can be expensive -- state transitions from page rw/ro frequently! Can we optimize?

Quoted 668 lines

kernel/livepatch/core.c new file +667 -0

+               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;
+
+       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;
+
+       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;
+
+       mutex_lock(&klp_mutex);
+
+       if (!klp_is_patch_registered(patch)) {
+               ret = -EINVAL;
+               goto err;
+       }
+
+       if (patch->state == KLP_DISABLED) {
+               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;
+
+       mutex_lock(&klp_mutex);
+
+       if (!klp_is_patch_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;
+
+       ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+       if (!ops)
+               return -ENOMEM;
+
+       ops->private = func;
+       ops->func = klp_ftrace_handler;
+       ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+       func->fops = ops;
+       func->state = KLP_DISABLED;
+
+       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);
+       kobject_put(obj->kobj);
+       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;
+
+       mutex_lock(&klp_mutex);
+
+       if (!klp_is_patch_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_initialized())
+               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;
+
+       ret = klp_init_object_loaded(patch, obj);
+       if (ret)
+               goto err;
+
+       if (patch->state == KLP_DISABLED)
+               return;
+
+       pr_notice("applying patch '%s' to loading module '%s'\n",
+                 pmod->name, mod->name);
+
+       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;
+
+       if (patch->state == KLP_DISABLED)
+               goto disabled;
+
+       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);
+
+disabled:
+       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) {
+               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;
+

kernel/livepatch/core.c line 929

Quoted 6 lines

kernel/livepatch/core.c new file +6 -0

+unregister:
+       unregister_module_notifier(&klp_module_nb);
+       return ret;
+}
+
+module_init(klp_init);

Looks good otherwise

Reviewed-by Balbir Singh <[email protected]>

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 <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

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 <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

The execution flow redirection related implemention in the livepatch ftrace handler is depended on the specific architecture. This patch introduces klp_arch_set_pc(like kgdb_arch_set_pc) interface to change the pt_regs.

Signed-off-by Li Bin <[email protected]>

The execution flow redirection related implemention in the livepatch ftrace handler is depended on the specific architecture. This patch introduces klp_arch_set_pc(like kgdb_arch_set_pc) interface to change the pt_regs.

Signed-off-by Li Bin <[email protected]>

The execution flow redirection related implemention in the livepatch ftrace handler is depended on the specific architecture. This patch introduces klp_arch_set_pc(like kgdb_arch_set_pc) interface to change the pt_regs.

Signed-off-by Li Bin <[email protected]>

---
 arch/x86/include/asm/livepatch.h |    5 +++++
 kernel/livepatch/core.c          |    2 +-
 2 files changed, 6 insertions(+), 1 deletions(-)

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 <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Add a sample live patching module.

Signed-off-by Seth Jennings <[email protected]>

Add a sample live patching module.

Signed-off-by Seth Jennings <[email protected]>

Changelog:

Thanks for all the feedback!

Quoted 5 lines · Seth Jennings

Changelog:

Thanks for all the feedback!

Could you describe what this does to signing? I presume the patched module should cause a taint on module signing?

Balbir Singh

Quoted 7 lines · Balbir Singh

Quoted 5 lines · Seth Jennings

Changelog:

Thanks for all the feedback!

Quoted 2 lines

Could you describe what this does to signing? I presume the patched module should cause a taint on module signing?

The patch module can be signed to avoid the taint of being unsigned, assuming you have the signing key for the kernel you are running. However we do taint with a new taint flag (see 1/3) to indicate that the kernel has been patched.

Could you describe what this does to signing? I presume the patched module should cause a taint on module signing?

Quoted 2 lines · Balbir Singh

Could you describe what this does to signing? I presume the patched module should cause a taint on module signing?

Hmm, why should it?

Quoted 4 lines

Quoted 2 lines

Could you describe what this does to signing? I presume the patched module should cause a taint on module signing?

Hmm, why should it?

I wanted to clarify it from a different perspective

If the base image is signed by X and the patched module is signed by Y, is that supported. What does it imply in the case of live-patching?

Quoted 5 lines · Balbir Singh

Quoted 4 lines

Quoted 2 lines

Could you describe what this does to signing? I presume the patched module should cause a taint on module signing?

Hmm, why should it?

Quoted 4 lines

I wanted to clarify it from a different perspective

If the base image is signed by X and the patched module is signed by Y, is that supported. What does it imply in the case of live-patching?

Why should that matter? Both are signed by keys that kernel is configured to trust, which makes them equal (even though they are technically different).

Quoted 12 lines · Jiri Kosina

Quoted 9 lines · Balbir Singh

Quoted 4 lines

Quoted 2 lines

Could you describe what this does to signing? I presume the patched module should cause a taint on module signing?

Hmm, why should it?

I wanted to clarify it from a different perspective

If the base image is signed by X and the patched module is signed by Y, is that supported. What does it imply in the case of live-patching?

Quoted 4 lines

Why should that matter? Both are signed by keys that kernel is configured to trust, which makes them equal (even though they are technically different).

I am not sure they are equal, others can comment

Changelog:

Thanks for all the feedback!

I think that we have something that is workable for everyone now. Barring functional defects, I think we should put a hold on any nits to avoid churn for the moment and start gathering acks so that we are in a position to go into -next when the 3.19 window closes.

Also, I don't think patches 1/3 and 3/3 have changed since v5, so if you reviewed them then, they haven't changed.

Quoted 9 lines · Seth Jennings

Changelog:

Thanks for all the feedback!

I think that we have something that is workable for everyone now. Barring functional defects, I think we should put a hold on any nits to avoid churn for the moment and start gathering acks so that we are in a position to go into -next when the 3.19 window closes.

Quoted 2 lines

Also, I don't think patches 1/3 and 3/3 have changed since v5, so if you reviewed them then, they haven't changed.

For the set:

Reviewed-by Josh Poimboeuf <[email protected]>

Changelog:

Thanks for all the feedback!

I think that we have something that is workable for everyone now. Barring functional defects, I think we should put a hold on any nits to avoid churn for the moment and start gathering acks so that we are in a position to go into -next when the 3.19 window closes.

Also, I don't think patches 1/3 and 3/3 have changed since v5, so if you reviewed them then, they haven't changed.

changes in v7:
- TODO: set IPMODIFY (not a blocker to moving forward)

Quoted 2 lines · Seth Jennings

changes in v7:
- TODO: set IPMODIFY (not a blocker to moving forward)

Why don't you set this?
IPMODIFY series are not completely applied yet, but you can already use the flag. All you need is just set it :)

Quoted 7 lines · Masami Hiramatsu

Quoted 2 lines · Seth Jennings

changes in v7:
- TODO: set IPMODIFY (not a blocker to moving forward)

Why don't you set this?
IPMODIFY series are not completely applied yet, but you can already use the flag. All you need is just set it :)

Yeah, I don't see any reason why we can't start using this flag now. How about we add this patch to the queue?

-->8--

Subject: livepatch: use FTRACE_OPS_FL_IPMODIFY

Use the FTRACE_OPS_FL_IPMODIFY flag to prevent conflicts with other ftrace users who also modify regs->ip.

Signed-off-by Josh Poimboeuf <[email protected]>

---
 kernel/livepatch/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

kernel/livepatch/core.c +2 -1

index 0004a71..bdd99975 100644
@@ -640,7 +640,8 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 
 	ops->private = func;
 	ops->func = klp_ftrace_handler;
-	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC |
+		     FTRACE_FL_IPMODIFY;
 	func->fops = ops;
 	func->state = KLP_DISABLED;
 

Quoted 7 lines · Masami Hiramatsu

Quoted 2 lines · Seth Jennings

changes in v7:
- TODO: set IPMODIFY (not a blocker to moving forward)

Why don't you set this?
IPMODIFY series are not completely applied yet, but you can already use the flag. All you need is just set it :)

Yeah, I don't see any reason why we can't start using this flag now. How about we add this patch to the queue?

-->8--

Subject: livepatch: use FTRACE_OPS_FL_IPMODIFY

Use the FTRACE_OPS_FL_IPMODIFY flag to prevent conflicts with other ftrace users who also modify regs->ip.

Signed-off-by Josh Poimboeuf <[email protected]>

---
 kernel/livepatch/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

kernel/livepatch/core.c +2 -1

index 0004a71..bdd99975 100644
@@ -640,7 +640,8 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 
 	ops->private = func;
 	ops->func = klp_ftrace_handler;
-	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC |
+		     FTRACE_FL_IPMODIFY;
 	func->fops = ops;
 	func->state = KLP_DISABLED;
 

Signature · 1 line

2.1.0

Quoted 16 lines · Josh Poimboeuf

Quoted 7 lines · Masami Hiramatsu

Quoted 2 lines · Seth Jennings

changes in v7:
- TODO: set IPMODIFY (not a blocker to moving forward)

Why don't you set this?
IPMODIFY series are not completely applied yet, but you can already use the flag. All you need is just set it :)

Yeah, I don't see any reason why we can't start using this flag now. How about we add this patch to the queue?

-->8--

Subject: livepatch: use FTRACE_OPS_FL_IPMODIFY

Quoted 4 lines

Use the FTRACE_OPS_FL_IPMODIFY flag to prevent conflicts with other ftrace users who also modify regs->ip.

Signed-off-by Josh Poimboeuf <[email protected]>

It makes sense. The flag is available even in 3.19.

Reviewed-by Petr Mladek <[email protected]>

Quoted 10 lines

---
 kernel/livepatch/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

kernel/livepatch/core.c +0 -0

index 0004a71..bdd99975 100644
@@ -640,7 +640,8 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 

kernel/livepatch/core.c static int klp_init_func(struct klp_object *obj, struct klp_func *func) · line 644

Quoted 5 lines

kernel/livepatch/core.c +2 -1

 	ops->private = func;
 	ops->func = klp_ftrace_handler;
-	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC |
+		     FTRACE_FL_IPMODIFY;

Quoted 6 lines

kernel/livepatch/core.c +0 -0

 	func->fops = ops;
 	func->state = KLP_DISABLED;
 

Signature · 1 line

2.1.0

--
To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

Quoted 17 lines · Petr Mladek

Quoted 16 lines · Josh Poimboeuf

Quoted 7 lines · Masami Hiramatsu

Quoted 2 lines · Seth Jennings

changes in v7:
- TODO: set IPMODIFY (not a blocker to moving forward)

Why don't you set this?
IPMODIFY series are not completely applied yet, but you can already use the flag. All you need is just set it :)

Yeah, I don't see any reason why we can't start using this flag now. How about we add this patch to the queue?

-->8--

Subject: livepatch: use FTRACE_OPS_FL_IPMODIFY

Quoted 8 lines

Quoted 4 lines

Use the FTRACE_OPS_FL_IPMODIFY flag to prevent conflicts with other ftrace users who also modify regs->ip.

Signed-off-by Josh Poimboeuf <[email protected]>

It makes sense. The flag is available even in 3.19.

Reviewed-by Petr Mladek <[email protected]>

Feel free to keep the Reviewed-by if you fix the typo, see below.

Quoted 10 lines

Quoted 10 lines

---
 kernel/livepatch/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

kernel/livepatch/core.c +0 -0

index 0004a71..bdd99975 100644
@@ -640,7 +640,8 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 

Quoted 5 lines

kernel/livepatch/core.c static int klp_init_func(struct klp_object *obj, struct klp_func *func) · line 644

Quoted 5 lines

kernel/livepatch/core.c +2 -1

 	ops->private = func;
 	ops->func = klp_ftrace_handler;
-	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC;
+	ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC |
+		     FTRACE_FL_IPMODIFY;

Heh, there is a typo. Please replace FTRACE_FL_IPMODIFY with FTRACE_OPS_FL_IPMODIFY ;-)