Re: [PATCHv7 2/3] kernel: add support for live patching

[Balbir Singh]

On Tue, Dec 16, 2014 at 11:28 PM, Seth Jennings <sjenning@xxxxxxxxxx> wrote:
> This commit introduces code for the live patching core.  It implements
> an ftrace-based mechanism and kernel interface for doing live patching
> of kernel and kernel module functions.
>
> It represents the greatest common functionality set between kpatch and
> kgraft and can accept patches built using either method.
>
> This first version does not implement any consistency mechanism that
> ensures that old and new code do not run together.  In practice, ~90% of
> CVEs are safe to apply in this way, since they simply add a conditional
> check.  However, any function change that can not execute safely with
> the old version of the function can _not_ be safely applied in this
> version.
>
> Signed-off-by: Seth Jennings <sjenning@xxxxxxxxxx>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

snip

> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index ce8dcdf..5c57181 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -17,6 +17,7 @@ config X86_64
>         depends on 64BIT
>         select X86_DEV_DMA_OPS
>         select ARCH_USE_CMPXCHG_LOCKREF
> +       select ARCH_HAVE_LIVE_PATCHING
>
>  ### Arch settings
>  config X86
> @@ -1986,6 +1987,8 @@ config CMDLINE_OVERRIDE
>           This is used to work around broken boot loaders.  This should
>           be set to 'N' under normal conditions.
>
> +source "kernel/livepatch/Kconfig"
> +
>  endmenu
>
>  config ARCH_ENABLE_MEMORY_HOTPLUG
> diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
> new file mode 100644
> index 0000000..c2ae592
> --- /dev/null
> +++ b/arch/x86/include/asm/livepatch.h
> @@ -0,0 +1,36 @@
> +/*
> + * livepatch.h - x86-specific Kernel Live Patching Core
> + *
> + * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef _ASM_X86_LIVEPATCH_H
> +#define _ASM_X86_LIVEPATCH_H
> +
> +#include <linux/module.h>
> +
> +#ifdef CONFIG_LIVE_PATCHING
> +#ifndef CC_USING_FENTRY
> +#error Your compiler must support -mfentry for live patching to work
> +#endif
> +extern int klp_write_module_reloc(struct module *mod, unsigned long type,
> +                                 unsigned long loc, unsigned long value);
> +
> +#else
> +#error Live patching support is disabled; check CONFIG_LIVE_PATCHING
> +#endif
> +
> +#endif /* _ASM_X86_LIVEPATCH_H */
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 5d4502c..316b34e 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -63,6 +63,7 @@ obj-$(CONFIG_X86_MPPARSE)     += mpparse.o
>  obj-y                          += apic/
>  obj-$(CONFIG_X86_REBOOTFIXUPS) += reboot_fixups_32.o
>  obj-$(CONFIG_DYNAMIC_FTRACE)   += ftrace.o
> +obj-$(CONFIG_LIVE_PATCHING)    += livepatch.o
>  obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
>  obj-$(CONFIG_FTRACE_SYSCALLS)  += ftrace.o
>  obj-$(CONFIG_X86_TSC)          += trace_clock.o
> diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
> new file mode 100644
> index 0000000..4b0ed7b
> --- /dev/null
> +++ b/arch/x86/kernel/livepatch.c
> @@ -0,0 +1,89 @@
> +/*
> + * livepatch.c - x86-specific Kernel Live Patching Core
> + *
> + * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/uaccess.h>
> +#include <asm/cacheflush.h>
> +#include <asm/page_types.h>
> +#include <asm/elf.h>
> +#include <asm/livepatch.h>
> +
> +/**
> + * klp_write_module_reloc() - write a relocation in a module
> + * @mod:       module in which the section to be modified is found
> + * @type:      ELF relocation type (see asm/elf.h)
> + * @loc:       address that the relocation should be written to
> + * @value:     relocation value (sym address + addend)
> + *
> + * This function writes a relocation to the specified location for
> + * a particular module.

This is more of the what then why?

> + */
> +int klp_write_module_reloc(struct module *mod, unsigned long type,
> +                          unsigned long loc, unsigned long value)
> +{
> +       int ret, numpages, size = 4;
> +       bool readonly;
> +       unsigned long val;
> +       unsigned long core = (unsigned long)mod->module_core;
> +       unsigned long core_ro_size = mod->core_ro_size;
> +       unsigned long core_size = mod->core_size;
> +
> +       switch (type) {
> +       case R_X86_64_NONE:
> +               return 0;
> +       case R_X86_64_64:
> +               val = value;
> +               size = 8;
> +               break;
> +       case R_X86_64_32:
> +               val = (u32)value;
> +               break;
> +       case R_X86_64_32S:
> +               val = (s32)value;
> +               break;
> +       case R_X86_64_PC32:
> +               val = (u32)(value - loc);
> +               break;
> +       default:
> +               /* unsupported relocation type */
> +               return -EINVAL;
> +       }
> +
> +       if (loc < core || loc >= core + core_size)
> +               /* loc does not point to any symbol inside the module */
> +               return -EINVAL;
> +
> +       if (loc < core + core_ro_size)
> +               readonly = true;
> +       else
> +               readonly = false;
> +
> +       /* determine if the relocation spans a page boundary */
> +       numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
> +
> +       if (readonly)
> +               set_memory_rw(loc & PAGE_MASK, numpages);
> +
> +       ret = probe_kernel_write((void *)loc, &val, size);
> +
> +       if (readonly)
> +               set_memory_ro(loc & PAGE_MASK, numpages);
> +
> +       return ret;
> +}
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> new file mode 100644
> index 0000000..b61fe74
> --- /dev/null
> +++ b/include/linux/livepatch.h
> @@ -0,0 +1,132 @@
> +/*
> + * livepatch.h - Kernel Live Patching Core
> + *
> + * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef _LINUX_LIVEPATCH_H_
> +#define _LINUX_LIVEPATCH_H_
> +
> +#include <linux/module.h>
> +#include <linux/ftrace.h>
> +
> +#if IS_ENABLED(CONFIG_LIVE_PATCHING)
> +
> +#include <asm/livepatch.h>
> +
> +enum klp_state {
> +       KLP_DISABLED,
> +       KLP_ENABLED
> +};
> +
> +/**
> + * struct klp_func - function structure for live patching
> + * @old_name:  name of the function to be patched
> + * @new_func:  pointer to the patched function code
> + * @old_addr:  a hint conveying at what address the old function
> + *             can be found (optional, vmlinux patches only)
> + * @kobj:      kobject for sysfs resources
> + * @fops:      ftrace operations structure
> + * @state:     tracks function-level patch application state
> + */
> +struct klp_func {
> +       /* external */
> +       const char *old_name;
> +       void *new_func;
> +       /*
> +        * The old_addr field is optional and can be used to resolve
> +        * duplicate symbol names in the vmlinux object.  If this
> +        * information is not present, the symbol is located by name
> +        * with kallsyms. If the name is not unique and old_addr is
> +        * not provided, the patch application fails as there is no
> +        * way to resolve the ambiguity.
> +        */
> +       unsigned long old_addr;
> +
> +       /* internal */
> +       struct kobject kobj;
> +       struct ftrace_ops *fops;
> +       enum klp_state state;
> +};
> +
> +/**
> + * struct klp_reloc - relocation structure for live patching
> + * @loc:       address where the relocation will be written
> + * @val:       address of the referenced symbol (optional,
> + *             vmlinux patches only)
> + * @type:      ELF relocation type
> + * @name:      name of the referenced symbol (for lookup/verification)
> + * @addend:    offset from the referenced symbol
> + * @external:  symbol is either exported or within the live patch module itself
> + */
> +struct klp_reloc {
> +       unsigned long loc;
> +       unsigned long val;
> +       unsigned long type;
> +       const char *name;
> +       int addend;
> +       int external;
> +};
> +
> +/**
> + * struct klp_object - kernel object structure for live patching
> + * @name:      module name (or NULL for vmlinux)
> + * @relocs:    relocation entries to be applied at load time
> + * @funcs:     function entries for functions to be patched in the object
> + * @kobj:      kobject for sysfs resources
> + * @mod:       kernel module associated with the patched object
> + *             (NULL for vmlinux)
> + * @state:     tracks object-level patch application state
> + */
> +struct klp_object {
> +       /* external */
> +       const char *name;
> +       struct klp_reloc *relocs;
> +       struct klp_func *funcs;
> +
> +       /* internal */
> +       struct kobject *kobj;
> +       struct module *mod;
> +       enum klp_state state;
> +};
> +
> +/**
> + * struct klp_patch - patch structure for live patching
> + * @mod:       reference to the live patch module
> + * @objs:      object entries for kernel objects to be patched
> + * @list:      list node for global list of registered patches
> + * @kobj:      kobject for sysfs resources
> + * @state:     tracks patch-level application state
> + */
> +struct klp_patch {
> +       /* external */
> +       struct module *mod;
> +       struct klp_object *objs;
> +
> +       /* internal */
> +       struct list_head list;
> +       struct kobject kobj;
> +       enum klp_state state;
> +};
> +
> +extern int klp_register_patch(struct klp_patch *);
> +extern int klp_unregister_patch(struct klp_patch *);
> +extern int klp_enable_patch(struct klp_patch *);
> +extern int klp_disable_patch(struct klp_patch *);
> +
> +#endif /* CONFIG_LIVE_PATCHING */
> +
> +#endif /* _LINUX_LIVEPATCH_H_ */
> diff --git a/kernel/Makefile b/kernel/Makefile
> index a59481a..616994f 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -26,6 +26,7 @@ obj-y += power/
>  obj-y += printk/
>  obj-y += irq/
>  obj-y += rcu/
> +obj-y += livepatch/
>
>  obj-$(CONFIG_CHECKPOINT_RESTORE) += kcmp.o
>  obj-$(CONFIG_FREEZER) += freezer.o
> diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
> new file mode 100644
> index 0000000..96da00f
> --- /dev/null
> +++ b/kernel/livepatch/Kconfig
> @@ -0,0 +1,18 @@
> +config ARCH_HAVE_LIVE_PATCHING
> +       boolean
> +       help
> +         Arch supports kernel live patching
> +
> +config LIVE_PATCHING
> +       boolean "Kernel Live Patching"
> +       depends on DYNAMIC_FTRACE_WITH_REGS
> +       depends on MODULES
> +       depends on SYSFS
> +       depends on KALLSYMS_ALL
> +       depends on ARCH_HAVE_LIVE_PATCHING
> +       help
> +         Say Y here if you want to support kernel live patching.
> +         This option has no runtime impact until a kernel "patch"
> +         module uses the interface provided by this option to register
> +         a patch, causing calls to patched functions to be redirected
> +         to new function code contained in the patch module.
> diff --git a/kernel/livepatch/Makefile b/kernel/livepatch/Makefile
> new file mode 100644
> index 0000000..7c1f008
> --- /dev/null
> +++ b/kernel/livepatch/Makefile
> @@ -0,0 +1,3 @@
> +obj-$(CONFIG_LIVE_PATCHING) += livepatch.o
> +
> +livepatch-objs := core.o
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> new file mode 100644
> index 0000000..0004a71
> --- /dev/null
> +++ b/kernel/livepatch/core.c
> @@ -0,0 +1,929 @@
> +/*
> + * core.c - Kernel Live Patching Core
> + *
> + * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +#include <linux/ftrace.h>
> +#include <linux/list.h>
> +#include <linux/kallsyms.h>
> +#include <linux/livepatch.h>
> +
> +/*
> + * 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;
> +       }
> +
> +       /* 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

> +static int klp_write_object_relocations(struct module *pmod,
> +                                       struct klp_object *obj)
> +{
> +       int ret;
> +       struct klp_reloc *reloc;
> +
> +       if (WARN_ON(!klp_is_object_loaded(obj)))
> +               return -EINVAL;
> +
> +       if (WARN_ON(!obj->relocs))
> +               return -EINVAL;
> +
> +       for (reloc = obj->relocs; reloc->name; reloc++) {
> +               if (!klp_is_module(obj)) {
> +                       ret = klp_verify_vmlinux_symbol(reloc->name,
> +                                                       reloc->val);
> +                       if (ret)
> +                               return ret;
> +               } else {
> +                       /* module, reloc->val needs to be discovered */
> +                       if (reloc->external)
> +                               ret = klp_find_external_symbol(pmod,
> +                                                              reloc->name,
> +                                                              &reloc->val);
> +                       else
> +                               ret = klp_find_object_symbol(obj->mod->name,
> +                                                            reloc->name,
> +                                                            &reloc->val);
> +                       if (ret)
> +                               return ret;
> +               }
> +               ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
> +                                            reloc->val + reloc->addend);

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

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

Looks good otherwise

Reviewed-by: Balbir Singh <bsingharora@xxxxxxxxx>
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