diff options
Diffstat (limited to 'kernel/livepatch')
| -rw-r--r-- | kernel/livepatch/Kconfig | 20 | ||||
| -rw-r--r-- | kernel/livepatch/Makefile | 4 | ||||
| -rw-r--r-- | kernel/livepatch/core.c | 1326 | ||||
| -rw-r--r-- | kernel/livepatch/core.h | 59 | ||||
| -rw-r--r-- | kernel/livepatch/patch.c | 289 | ||||
| -rw-r--r-- | kernel/livepatch/patch.h | 35 | ||||
| -rw-r--r-- | kernel/livepatch/shadow.c | 299 | ||||
| -rw-r--r-- | kernel/livepatch/state.c | 119 | ||||
| -rw-r--r-- | kernel/livepatch/state.h | 9 | ||||
| -rw-r--r-- | kernel/livepatch/transition.c | 752 | ||||
| -rw-r--r-- | kernel/livepatch/transition.h | 16 |
11 files changed, 2928 insertions, 0 deletions
diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig new file mode 100644 index 0000000000..53d51ed619 --- /dev/null +++ b/kernel/livepatch/Kconfig @@ -0,0 +1,20 @@ +# SPDX-License-Identifier: GPL-2.0-only +config HAVE_LIVEPATCH + bool + help + Arch supports kernel live patching + +config LIVEPATCH + bool "Kernel Live Patching" + depends on DYNAMIC_FTRACE_WITH_REGS || DYNAMIC_FTRACE_WITH_ARGS + depends on MODULES + depends on SYSFS + depends on KALLSYMS_ALL + depends on HAVE_LIVEPATCH + depends on !TRIM_UNUSED_KSYMS + 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 0000000000..cf03d4bdfc --- /dev/null +++ b/kernel/livepatch/Makefile @@ -0,0 +1,4 @@ +# SPDX-License-Identifier: GPL-2.0-only +obj-$(CONFIG_LIVEPATCH) += livepatch.o + +livepatch-objs := core.o patch.o shadow.o state.o transition.o diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c new file mode 100644 index 0000000000..ecbc9b6aba --- /dev/null +++ b/kernel/livepatch/core.c @@ -0,0 +1,1326 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * core.c - Kernel Live Patching Core + * + * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> + * Copyright (C) 2014 SUSE + */ + +#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/list.h> +#include <linux/kallsyms.h> +#include <linux/livepatch.h> +#include <linux/elf.h> +#include <linux/moduleloader.h> +#include <linux/completion.h> +#include <linux/memory.h> +#include <linux/rcupdate.h> +#include <asm/cacheflush.h> +#include "core.h" +#include "patch.h" +#include "state.h" +#include "transition.h" + +/* + * klp_mutex is a coarse lock which serializes access to klp data. All + * accesses to klp-related variables and structures must have mutex protection, + * except within the following functions which carefully avoid the need for it: + * + * - klp_ftrace_handler() + * - klp_update_patch_state() + * - __klp_sched_try_switch() + */ +DEFINE_MUTEX(klp_mutex); + +/* + * Actively used patches: enabled or in transition. Note that replaced + * or disabled patches are not listed even though the related kernel + * module still can be loaded. + */ +LIST_HEAD(klp_patches); + +static struct kobject *klp_root_kobj; + +static bool klp_is_module(struct klp_object *obj) +{ + return obj->name; +} + +/* sets obj->mod if object is not vmlinux and module is found */ +static void klp_find_object_module(struct klp_object *obj) +{ + struct module *mod; + + if (!klp_is_module(obj)) + return; + + rcu_read_lock_sched(); + /* + * We do not want to block removal of patched modules and therefore + * we do not take a reference here. The patches are removed by + * klp_module_going() instead. + */ + mod = find_module(obj->name); + /* + * Do not mess work of klp_module_coming() and klp_module_going(). + * Note that the patch might still be needed before klp_module_going() + * is called. Module functions can be called even in the GOING state + * until mod->exit() finishes. This is especially important for + * patches that modify semantic of the functions. + */ + if (mod && mod->klp_alive) + obj->mod = mod; + + rcu_read_unlock_sched(); +} + +static bool klp_initialized(void) +{ + return !!klp_root_kobj; +} + +static struct klp_func *klp_find_func(struct klp_object *obj, + struct klp_func *old_func) +{ + struct klp_func *func; + + klp_for_each_func(obj, func) { + if ((strcmp(old_func->old_name, func->old_name) == 0) && + (old_func->old_sympos == func->old_sympos)) { + return func; + } + } + + return NULL; +} + +static struct klp_object *klp_find_object(struct klp_patch *patch, + struct klp_object *old_obj) +{ + struct klp_object *obj; + + klp_for_each_object(patch, obj) { + if (klp_is_module(old_obj)) { + if (klp_is_module(obj) && + strcmp(old_obj->name, obj->name) == 0) { + return obj; + } + } else if (!klp_is_module(obj)) { + return obj; + } + } + + return NULL; +} + +struct klp_find_arg { + const char *name; + unsigned long addr; + unsigned long count; + unsigned long pos; +}; + +static int klp_match_callback(void *data, unsigned long addr) +{ + struct klp_find_arg *args = data; + + args->addr = addr; + args->count++; + + /* + * Finish the search when the symbol is found for the desired position + * or the position is not defined for a non-unique symbol. + */ + if ((args->pos && (args->count == args->pos)) || + (!args->pos && (args->count > 1))) + return 1; + + return 0; +} + +static int klp_find_callback(void *data, const char *name, unsigned long addr) +{ + struct klp_find_arg *args = data; + + if (strcmp(args->name, name)) + return 0; + + return klp_match_callback(data, addr); +} + +static int klp_find_object_symbol(const char *objname, const char *name, + unsigned long sympos, unsigned long *addr) +{ + struct klp_find_arg args = { + .name = name, + .addr = 0, + .count = 0, + .pos = sympos, + }; + + if (objname) + module_kallsyms_on_each_symbol(objname, klp_find_callback, &args); + else + kallsyms_on_each_match_symbol(klp_match_callback, name, &args); + + /* + * Ensure an address was found. If sympos is 0, ensure symbol is unique; + * otherwise ensure the symbol position count matches sympos. + */ + if (args.addr == 0) + pr_err("symbol '%s' not found in symbol table\n", name); + else if (args.count > 1 && sympos == 0) { + pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n", + name, objname); + } else if (sympos != args.count && sympos > 0) { + pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n", + sympos, name, objname ? objname : "vmlinux"); + } else { + *addr = args.addr; + return 0; + } + + *addr = 0; + return -EINVAL; +} + +static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab, + unsigned int symndx, Elf_Shdr *relasec, + const char *sec_objname) +{ + int i, cnt, ret; + char sym_objname[MODULE_NAME_LEN]; + char sym_name[KSYM_NAME_LEN]; + Elf_Rela *relas; + Elf_Sym *sym; + unsigned long sympos, addr; + bool sym_vmlinux; + bool sec_vmlinux = !strcmp(sec_objname, "vmlinux"); + + /* + * Since the field widths for sym_objname and sym_name in the sscanf() + * call are hard-coded and correspond to MODULE_NAME_LEN and + * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN + * and KSYM_NAME_LEN have the values we expect them to have. + * + * Because the value of MODULE_NAME_LEN can differ among architectures, + * we use the smallest/strictest upper bound possible (56, based on + * the current definition of MODULE_NAME_LEN) to prevent overflows. + */ + BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512); + + relas = (Elf_Rela *) relasec->sh_addr; + /* For each rela in this klp relocation section */ + for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) { + sym = (Elf_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info); + if (sym->st_shndx != SHN_LIVEPATCH) { + pr_err("symbol %s is not marked as a livepatch symbol\n", + strtab + sym->st_name); + return -EINVAL; + } + + /* Format: .klp.sym.sym_objname.sym_name,sympos */ + cnt = sscanf(strtab + sym->st_name, + ".klp.sym.%55[^.].%511[^,],%lu", + sym_objname, sym_name, &sympos); + if (cnt != 3) { + pr_err("symbol %s has an incorrectly formatted name\n", + strtab + sym->st_name); + return -EINVAL; + } + + sym_vmlinux = !strcmp(sym_objname, "vmlinux"); + + /* + * Prevent module-specific KLP rela sections from referencing + * vmlinux symbols. This helps prevent ordering issues with + * module special section initializations. Presumably such + * symbols are exported and normal relas can be used instead. + */ + if (!sec_vmlinux && sym_vmlinux) { + pr_err("invalid access to vmlinux symbol '%s' from module-specific livepatch relocation section\n", + sym_name); + return -EINVAL; + } + + /* klp_find_object_symbol() treats a NULL objname as vmlinux */ + ret = klp_find_object_symbol(sym_vmlinux ? NULL : sym_objname, + sym_name, sympos, &addr); + if (ret) + return ret; + + sym->st_value = addr; + } + + return 0; +} + +void __weak clear_relocate_add(Elf_Shdr *sechdrs, + const char *strtab, + unsigned int symindex, + unsigned int relsec, + struct module *me) +{ +} + +/* + * At a high-level, there are two types of klp relocation sections: those which + * reference symbols which live in vmlinux; and those which reference symbols + * which live in other modules. This function is called for both types: + * + * 1) When a klp module itself loads, the module code calls this function to + * write vmlinux-specific klp relocations (.klp.rela.vmlinux.* sections). + * These relocations are written to the klp module text to allow the patched + * code/data to reference unexported vmlinux symbols. They're written as + * early as possible to ensure that other module init code (.e.g., + * jump_label_apply_nops) can access any unexported vmlinux symbols which + * might be referenced by the klp module's special sections. + * + * 2) When a to-be-patched module loads -- or is already loaded when a + * corresponding klp module loads -- klp code calls this function to write + * module-specific klp relocations (.klp.rela.{module}.* sections). These + * are written to the klp module text to allow the patched code/data to + * reference symbols which live in the to-be-patched module or one of its + * module dependencies. Exported symbols are supported, in addition to + * unexported symbols, in order to enable late module patching, which allows + * the to-be-patched module to be loaded and patched sometime *after* the + * klp module is loaded. + */ +static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, + const char *shstrtab, const char *strtab, + unsigned int symndx, unsigned int secndx, + const char *objname, bool apply) +{ + int cnt, ret; + char sec_objname[MODULE_NAME_LEN]; + Elf_Shdr *sec = sechdrs + secndx; + + /* + * Format: .klp.rela.sec_objname.section_name + * See comment in klp_resolve_symbols() for an explanation + * of the selected field width value. + */ + cnt = sscanf(shstrtab + sec->sh_name, ".klp.rela.%55[^.]", + sec_objname); + if (cnt != 1) { + pr_err("section %s has an incorrectly formatted name\n", + shstrtab + sec->sh_name); + return -EINVAL; + } + + if (strcmp(objname ? objname : "vmlinux", sec_objname)) + return 0; + + if (apply) { + ret = klp_resolve_symbols(sechdrs, strtab, symndx, + sec, sec_objname); + if (ret) + return ret; + + return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod); + } + + clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod); + return 0; +} + +int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, + const char *shstrtab, const char *strtab, + unsigned int symndx, unsigned int secndx, + const char *objname) +{ + return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx, + secndx, objname, true); +} + +/* + * Sysfs Interface + * + * /sys/kernel/livepatch + * /sys/kernel/livepatch/<patch> + * /sys/kernel/livepatch/<patch>/enabled + * /sys/kernel/livepatch/<patch>/transition + * /sys/kernel/livepatch/<patch>/force + * /sys/kernel/livepatch/<patch>/<object> + * /sys/kernel/livepatch/<patch>/<object>/patched + * /sys/kernel/livepatch/<patch>/<object>/<function,sympos> + */ +static int __klp_disable_patch(struct klp_patch *patch); + +static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t count) +{ + struct klp_patch *patch; + int ret; + bool enabled; + + ret = kstrtobool(buf, &enabled); + if (ret) + return ret; + + patch = container_of(kobj, struct klp_patch, kobj); + + mutex_lock(&klp_mutex); + + if (patch->enabled == enabled) { + /* already in requested state */ + ret = -EINVAL; + goto out; + } + + /* + * Allow to reverse a pending transition in both ways. It might be + * necessary to complete the transition without forcing and breaking + * the system integrity. + * + * Do not allow to re-enable a disabled patch. + */ + if (patch == klp_transition_patch) + klp_reverse_transition(); + else if (!enabled) + ret = __klp_disable_patch(patch); + else + ret = -EINVAL; + +out: + mutex_unlock(&klp_mutex); + + if (ret) + return ret; + return count; +} + +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->enabled); +} + +static ssize_t transition_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 == klp_transition_patch); +} + +static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t count) +{ + struct klp_patch *patch; + int ret; + bool val; + + ret = kstrtobool(buf, &val); + if (ret) + return ret; + + if (!val) + return count; + + mutex_lock(&klp_mutex); + + patch = container_of(kobj, struct klp_patch, kobj); + if (patch != klp_transition_patch) { + mutex_unlock(&klp_mutex); + return -EINVAL; + } + + klp_force_transition(); + + mutex_unlock(&klp_mutex); + + return count; +} + +static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled); +static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition); +static struct kobj_attribute force_kobj_attr = __ATTR_WO(force); +static struct attribute *klp_patch_attrs[] = { + &enabled_kobj_attr.attr, + &transition_kobj_attr.attr, + &force_kobj_attr.attr, + NULL +}; +ATTRIBUTE_GROUPS(klp_patch); + +static ssize_t patched_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + struct klp_object *obj; + + obj = container_of(kobj, struct klp_object, kobj); + return sysfs_emit(buf, "%d\n", obj->patched); +} + +static struct kobj_attribute patched_kobj_attr = __ATTR_RO(patched); +static struct attribute *klp_object_attrs[] = { + &patched_kobj_attr.attr, + NULL, +}; +ATTRIBUTE_GROUPS(klp_object); + +static void klp_free_object_dynamic(struct klp_object *obj) +{ + kfree(obj->name); + kfree(obj); +} + +static void klp_init_func_early(struct klp_object *obj, + struct klp_func *func); +static void klp_init_object_early(struct klp_patch *patch, + struct klp_object *obj); + +static struct klp_object *klp_alloc_object_dynamic(const char *name, + struct klp_patch *patch) +{ + struct klp_object *obj; + + obj = kzalloc(sizeof(*obj), GFP_KERNEL); + if (!obj) + return NULL; + + if (name) { + obj->name = kstrdup(name, GFP_KERNEL); + if (!obj->name) { + kfree(obj); + return NULL; + } + } + + klp_init_object_early(patch, obj); + obj->dynamic = true; + + return obj; +} + +static void klp_free_func_nop(struct klp_func *func) +{ + kfree(func->old_name); + kfree(func); +} + +static struct klp_func *klp_alloc_func_nop(struct klp_func *old_func, + struct klp_object *obj) +{ + struct klp_func *func; + + func = kzalloc(sizeof(*func), GFP_KERNEL); + if (!func) + return NULL; + + if (old_func->old_name) { + func->old_name = kstrdup(old_func->old_name, GFP_KERNEL); + if (!func->old_name) { + kfree(func); + return NULL; + } + } + + klp_init_func_early(obj, func); + /* + * func->new_func is same as func->old_func. These addresses are + * set when the object is loaded, see klp_init_object_loaded(). + */ + func->old_sympos = old_func->old_sympos; + func->nop = true; + + return func; +} + +static int klp_add_object_nops(struct klp_patch *patch, + struct klp_object *old_obj) +{ + struct klp_object *obj; + struct klp_func *func, *old_func; + + obj = klp_find_object(patch, old_obj); + + if (!obj) { + obj = klp_alloc_object_dynamic(old_obj->name, patch); + if (!obj) + return -ENOMEM; + } + + klp_for_each_func(old_obj, old_func) { + func = klp_find_func(obj, old_func); + if (func) + continue; + + func = klp_alloc_func_nop(old_func, obj); + if (!func) + return -ENOMEM; + } + + return 0; +} + +/* + * Add 'nop' functions which simply return to the caller to run + * the original function. The 'nop' functions are added to a + * patch to facilitate a 'replace' mode. + */ +static int klp_add_nops(struct klp_patch *patch) +{ + struct klp_patch *old_patch; + struct klp_object *old_obj; + + klp_for_each_patch(old_patch) { + klp_for_each_object(old_patch, old_obj) { + int err; + + err = klp_add_object_nops(patch, old_obj); + if (err) + return err; + } + } + + return 0; +} + +static void klp_kobj_release_patch(struct kobject *kobj) +{ + struct klp_patch *patch; + + patch = container_of(kobj, struct klp_patch, kobj); + complete(&patch->finish); +} + +static const struct kobj_type klp_ktype_patch = { + .release = klp_kobj_release_patch, + .sysfs_ops = &kobj_sysfs_ops, + .default_groups = klp_patch_groups, +}; + +static void klp_kobj_release_object(struct kobject *kobj) +{ + struct klp_object *obj; + + obj = container_of(kobj, struct klp_object, kobj); + + if (obj->dynamic) + klp_free_object_dynamic(obj); +} + +static const struct kobj_type klp_ktype_object = { + .release = klp_kobj_release_object, + .sysfs_ops = &kobj_sysfs_ops, + .default_groups = klp_object_groups, +}; + +static void klp_kobj_release_func(struct kobject *kobj) +{ + struct klp_func *func; + + func = container_of(kobj, struct klp_func, kobj); + + if (func->nop) + klp_free_func_nop(func); +} + +static const struct kobj_type klp_ktype_func = { + .release = klp_kobj_release_func, + .sysfs_ops = &kobj_sysfs_ops, +}; + +static void __klp_free_funcs(struct klp_object *obj, bool nops_only) +{ + struct klp_func *func, *tmp_func; + + klp_for_each_func_safe(obj, func, tmp_func) { + if (nops_only && !func->nop) + continue; + + list_del(&func->node); + 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; + + klp_for_each_func(obj, func) { + func->old_func = NULL; + + if (func->nop) + func->new_func = NULL; + } +} + +static void __klp_free_objects(struct klp_patch *patch, bool nops_only) +{ + struct klp_object *obj, *tmp_obj; + + klp_for_each_object_safe(patch, obj, tmp_obj) { + __klp_free_funcs(obj, nops_only); + + if (nops_only && !obj->dynamic) + continue; + + list_del(&obj->node); + kobject_put(&obj->kobj); + } +} + +static void klp_free_objects(struct klp_patch *patch) +{ + __klp_free_objects(patch, false); +} + +static void klp_free_objects_dynamic(struct klp_patch *patch) +{ + __klp_free_objects(patch, true); +} + +/* + * This function implements the free operations that can be called safely + * under klp_mutex. + * + * The operation must be completed by calling klp_free_patch_finish() + * outside klp_mutex. + */ +static void klp_free_patch_start(struct klp_patch *patch) +{ + if (!list_empty(&patch->list)) + list_del(&patch->list); + + klp_free_objects(patch); +} + +/* + * This function implements the free part that must be called outside + * klp_mutex. + * + * It must be called after klp_free_patch_start(). And it has to be + * the last function accessing the livepatch structures when the patch + * gets disabled. + */ +static void klp_free_patch_finish(struct klp_patch *patch) +{ + /* + * Avoid deadlock with enabled_store() sysfs callback by + * calling this outside klp_mutex. It is safe because + * this is called when the patch gets disabled and it + * cannot get enabled again. + */ + kobject_put(&patch->kobj); + wait_for_completion(&patch->finish); + + /* Put the module after the last access to struct klp_patch. */ + if (!patch->forced) + module_put(patch->mod); +} + +/* + * The livepatch might be freed from sysfs interface created by the patch. + * This work allows to wait until the interface is destroyed in a separate + * context. + */ +static void klp_free_patch_work_fn(struct work_struct *work) +{ + struct klp_patch *patch = + container_of(work, struct klp_patch, free_work); + + klp_free_patch_finish(patch); +} + +void klp_free_patch_async(struct klp_patch *patch) +{ + klp_free_patch_start(patch); + schedule_work(&patch->free_work); +} + +void klp_free_replaced_patches_async(struct klp_patch *new_patch) +{ + struct klp_patch *old_patch, *tmp_patch; + + klp_for_each_patch_safe(old_patch, tmp_patch) { + if (old_patch == new_patch) + return; + klp_free_patch_async(old_patch); + } +} + +static int klp_init_func(struct klp_object *obj, struct klp_func *func) +{ + if (!func->old_name) + return -EINVAL; + + /* + * NOPs get the address later. The patched module must be loaded, + * see klp_init_object_loaded(). + */ + if (!func->new_func && !func->nop) + return -EINVAL; + + if (strlen(func->old_name) >= KSYM_NAME_LEN) + return -EINVAL; + + INIT_LIST_HEAD(&func->stack_node); + func->patched = false; + func->transition = false; + + /* The format for the sysfs directory is <function,sympos> where sympos + * is the nth occurrence of this symbol in kallsyms for the patched + * object. If the user selects 0 for old_sympos, then 1 will be used + * since a unique symbol will be the first occurrence. + */ + return kobject_add(&func->kobj, &obj->kobj, "%s,%lu", + func->old_name, + func->old_sympos ? func->old_sympos : 1); +} + +static int klp_write_object_relocs(struct klp_patch *patch, + struct klp_object *obj, + bool apply) +{ + int i, ret; + struct klp_modinfo *info = patch->mod->klp_info; + + for (i = 1; i < info->hdr.e_shnum; i++) { + Elf_Shdr *sec = info->sechdrs + i; + + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH)) + continue; + + ret = klp_write_section_relocs(patch->mod, info->sechdrs, + info->secstrings, + patch->mod->core_kallsyms.strtab, + info->symndx, i, obj->name, apply); + if (ret) + return ret; + } + + return 0; +} + +static int klp_apply_object_relocs(struct klp_patch *patch, + struct klp_object *obj) +{ + return klp_write_object_relocs(patch, obj, true); +} + +static void klp_clear_object_relocs(struct klp_patch *patch, + struct klp_object *obj) +{ + klp_write_object_relocs(patch, obj, false); +} + +/* 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 (klp_is_module(obj)) { + /* + * Only write module-specific relocations here + * (.klp.rela.{module}.*). vmlinux-specific relocations were + * written earlier during the initialization of the klp module + * itself. + */ + ret = klp_apply_object_relocs(patch, obj); + if (ret) + return ret; + } + + klp_for_each_func(obj, func) { + ret = klp_find_object_symbol(obj->name, func->old_name, + func->old_sympos, + (unsigned long *)&func->old_func); + if (ret) + return ret; + + ret = kallsyms_lookup_size_offset((unsigned long)func->old_func, + &func->old_size, NULL); + if (!ret) { + pr_err("kallsyms size lookup failed for '%s'\n", + func->old_name); + return -ENOENT; + } + + if (func->nop) + func->new_func = func->old_func; + + ret = kallsyms_lookup_size_offset((unsigned long)func->new_func, + &func->new_size, NULL); + if (!ret) { + pr_err("kallsyms size lookup failed for '%s' replacement\n", + func->old_name); + return -ENOENT; + } + } + + 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 (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN) + return -EINVAL; + + obj->patched = false; + obj->mod = NULL; + + klp_find_object_module(obj); + + name = klp_is_module(obj) ? obj->name : "vmlinux"; + ret = kobject_add(&obj->kobj, &patch->kobj, "%s", name); + if (ret) + return ret; + + klp_for_each_func(obj, func) { + ret = klp_init_func(obj, func); + if (ret) + return ret; + } + + if (klp_is_object_loaded(obj)) + ret = klp_init_object_loaded(patch, obj); + + return ret; +} + +static void klp_init_func_early(struct klp_object *obj, + struct klp_func *func) +{ + kobject_init(&func->kobj, &klp_ktype_func); + list_add_tail(&func->node, &obj->func_list); +} + +static void klp_init_object_early(struct klp_patch *patch, + struct klp_object *obj) +{ + INIT_LIST_HEAD(&obj->func_list); + kobject_init(&obj->kobj, &klp_ktype_object); + list_add_tail(&obj->node, &patch->obj_list); +} + +static void klp_init_patch_early(struct klp_patch *patch) +{ + struct klp_object *obj; + struct klp_func *func; + + INIT_LIST_HEAD(&patch->list); + INIT_LIST_HEAD(&patch->obj_list); + kobject_init(&patch->kobj, &klp_ktype_patch); + patch->enabled = false; + patch->forced = false; + INIT_WORK(&patch->free_work, klp_free_patch_work_fn); + init_completion(&patch->finish); + + klp_for_each_object_static(patch, obj) { + klp_init_object_early(patch, obj); + + klp_for_each_func_static(obj, func) { + klp_init_func_early(obj, func); + } + } +} + +static int klp_init_patch(struct klp_patch *patch) +{ + struct klp_object *obj; + int ret; + + ret = kobject_add(&patch->kobj, klp_root_kobj, "%s", patch->mod->name); + if (ret) + return ret; + + if (patch->replace) { + ret = klp_add_nops(patch); + if (ret) + return ret; + } + + klp_for_each_object(patch, obj) { + ret = klp_init_object(patch, obj); + if (ret) + return ret; + } + + list_add_tail(&patch->list, &klp_patches); + + return 0; +} + +static int __klp_disable_patch(struct klp_patch *patch) +{ + struct klp_object *obj; + + if (WARN_ON(!patch->enabled)) + return -EINVAL; + + if (klp_transition_patch) + return -EBUSY; + + klp_init_transition(patch, KLP_UNPATCHED); + + klp_for_each_object(patch, obj) + if (obj->patched) + klp_pre_unpatch_callback(obj); + + /* + * Enforce the order of the func->transition writes in + * klp_init_transition() and the TIF_PATCH_PENDING writes in + * klp_start_transition(). In the rare case where klp_ftrace_handler() + * is called shortly after klp_update_patch_state() switches the task, + * this ensures the handler sees that func->transition is set. + */ + smp_wmb(); + + klp_start_transition(); + patch->enabled = false; + klp_try_complete_transition(); + + return 0; +} + +static int __klp_enable_patch(struct klp_patch *patch) +{ + struct klp_object *obj; + int ret; + + if (klp_transition_patch) + return -EBUSY; + + if (WARN_ON(patch->enabled)) + return -EINVAL; + + pr_notice("enabling patch '%s'\n", patch->mod->name); + + klp_init_transition(patch, KLP_PATCHED); + + /* + * Enforce the order of the func->transition writes in + * klp_init_transition() and the ops->func_stack writes in + * klp_patch_object(), so that klp_ftrace_handler() will see the + * func->transition updates before the handler is registered and the + * new funcs become visible to the handler. + */ + smp_wmb(); + + klp_for_each_object(patch, obj) { + if (!klp_is_object_loaded(obj)) + continue; + + ret = klp_pre_patch_callback(obj); + if (ret) { + pr_warn("pre-patch callback failed for object '%s'\n", + klp_is_module(obj) ? obj->name : "vmlinux"); + goto err; + } + + ret = klp_patch_object(obj); + if (ret) { + pr_warn("failed to patch object '%s'\n", + klp_is_module(obj) ? obj->name : "vmlinux"); + goto err; + } + } + + klp_start_transition(); + patch->enabled = true; + klp_try_complete_transition(); + + return 0; +err: + pr_warn("failed to enable patch '%s'\n", patch->mod->name); + + klp_cancel_transition(); + return ret; +} + +/** + * klp_enable_patch() - enable the livepatch + * @patch: patch to be enabled + * + * Initializes the data structure associated with the patch, creates the sysfs + * interface, performs the needed symbol lookups and code relocations, + * registers the patched functions with ftrace. + * + * This function is supposed to be called from the livepatch module_init() + * callback. + * + * Return: 0 on success, otherwise error + */ +int klp_enable_patch(struct klp_patch *patch) +{ + int ret; + struct klp_object *obj; + + if (!patch || !patch->mod || !patch->objs) + return -EINVAL; + + klp_for_each_object_static(patch, obj) { + if (!obj->funcs) + return -EINVAL; + } + + + if (!is_livepatch_module(patch->mod)) { + pr_err("module %s is not marked as a livepatch module\n", + patch->mod->name); + return -EINVAL; + } + + if (!klp_initialized()) + return -ENODEV; + + if (!klp_have_reliable_stack()) { + pr_warn("This architecture doesn't have support for the livepatch consistency model.\n"); + pr_warn("The livepatch transition may never complete.\n"); + } + + mutex_lock(&klp_mutex); + + if (!klp_is_patch_compatible(patch)) { + pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n", + patch->mod->name); + mutex_unlock(&klp_mutex); + return -EINVAL; + } + + if (!try_module_get(patch->mod)) { + mutex_unlock(&klp_mutex); + return -ENODEV; + } + + klp_init_patch_early(patch); + + ret = klp_init_patch(patch); + if (ret) + goto err; + + ret = __klp_enable_patch(patch); + if (ret) + goto err; + + mutex_unlock(&klp_mutex); + + return 0; + +err: + klp_free_patch_start(patch); + + mutex_unlock(&klp_mutex); + + klp_free_patch_finish(patch); + + return ret; +} +EXPORT_SYMBOL_GPL(klp_enable_patch); + +/* + * This function unpatches objects from the replaced livepatches. + * + * We could be pretty aggressive here. It is called in the situation where + * these structures are no longer accessed from the ftrace handler. + * All functions are redirected by the klp_transition_patch. They + * use either a new code or they are in the original code because + * of the special nop function patches. + * + * The only exception is when the transition was forced. In this case, + * klp_ftrace_handler() might still see the replaced patch on the stack. + * Fortunately, it is carefully designed to work with removed functions + * thanks to RCU. We only have to keep the patches on the system. Also + * this is handled transparently by patch->module_put. + */ +void klp_unpatch_replaced_patches(struct klp_patch *new_patch) +{ + struct klp_patch *old_patch; + + klp_for_each_patch(old_patch) { + if (old_patch == new_patch) + return; + + old_patch->enabled = false; + klp_unpatch_objects(old_patch); + } +} + +/* + * This function removes the dynamically allocated 'nop' functions. + * + * We could be pretty aggressive. NOPs do not change the existing + * behavior except for adding unnecessary delay by the ftrace handler. + * + * It is safe even when the transition was forced. The ftrace handler + * will see a valid ops->func_stack entry thanks to RCU. + * + * We could even free the NOPs structures. They must be the last entry + * in ops->func_stack. Therefore unregister_ftrace_function() is called. + * It does the same as klp_synchronize_transition() to make sure that + * nobody is inside the ftrace handler once the operation finishes. + * + * IMPORTANT: It must be called right after removing the replaced patches! + */ +void klp_discard_nops(struct klp_patch *new_patch) +{ + klp_unpatch_objects_dynamic(klp_transition_patch); + klp_free_objects_dynamic(klp_transition_patch); +} + +/* + * Remove parts of patches that touch a given kernel module. The list of + * patches processed might be limited. When limit is NULL, all patches + * will be handled. + */ +static void klp_cleanup_module_patches_limited(struct module *mod, + struct klp_patch *limit) +{ + struct klp_patch *patch; + struct klp_object *obj; + + klp_for_each_patch(patch) { + if (patch == limit) + break; + + klp_for_each_object(patch, obj) { + if (!klp_is_module(obj) || strcmp(obj->name, mod->name)) + continue; + + if (patch != klp_transition_patch) + klp_pre_unpatch_callback(obj); + + pr_notice("reverting patch '%s' on unloading module '%s'\n", + patch->mod->name, obj->mod->name); + klp_unpatch_object(obj); + + klp_post_unpatch_callback(obj); + klp_clear_object_relocs(patch, obj); + klp_free_object_loaded(obj); + break; + } + } +} + +int klp_module_coming(struct module *mod) +{ + int ret; + struct klp_patch *patch; + struct klp_object *obj; + + if (WARN_ON(mod->state != MODULE_STATE_COMING)) + return -EINVAL; + + if (!strcmp(mod->name, "vmlinux")) { + pr_err("vmlinux.ko: invalid module name\n"); + return -EINVAL; + } + + mutex_lock(&klp_mutex); + /* + * Each module has to know that klp_module_coming() + * has been called. We never know what module will + * get patched by a new patch. + */ + mod->klp_alive = true; + + klp_for_each_patch(patch) { + klp_for_each_object(patch, obj) { + if (!klp_is_module(obj) || strcmp(obj->name, mod->name)) + continue; + + obj->mod = mod; + + ret = klp_init_object_loaded(patch, obj); + if (ret) { + pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n", + patch->mod->name, obj->mod->name, ret); + goto err; + } + + pr_notice("applying patch '%s' to loading module '%s'\n", + patch->mod->name, obj->mod->name); + + ret = klp_pre_patch_callback(obj); + if (ret) { + pr_warn("pre-patch callback failed for object '%s'\n", + obj->name); + goto err; + } + + ret = klp_patch_object(obj); + if (ret) { + pr_warn("failed to apply patch '%s' to module '%s' (%d)\n", + patch->mod->name, obj->mod->name, ret); + + klp_post_unpatch_callback(obj); + goto err; + } + + if (patch != klp_transition_patch) + klp_post_patch_callback(obj); + + break; + } + } + + mutex_unlock(&klp_mutex); + + return 0; + +err: + /* + * If a patch is unsuccessfully applied, return + * error to the module loader. + */ + pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n", + patch->mod->name, obj->mod->name, obj->mod->name); + mod->klp_alive = false; + obj->mod = NULL; + klp_cleanup_module_patches_limited(mod, patch); + mutex_unlock(&klp_mutex); + + return ret; +} + +void klp_module_going(struct module *mod) +{ + if (WARN_ON(mod->state != MODULE_STATE_GOING && + mod->state != MODULE_STATE_COMING)) + return; + + mutex_lock(&klp_mutex); + /* + * Each module has to know that klp_module_going() + * has been called. We never know what module will + * get patched by a new patch. + */ + mod->klp_alive = false; + + klp_cleanup_module_patches_limited(mod, NULL); + + mutex_unlock(&klp_mutex); +} + +static int __init klp_init(void) +{ + klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj); + if (!klp_root_kobj) + return -ENOMEM; + + return 0; +} + +module_init(klp_init); diff --git a/kernel/livepatch/core.h b/kernel/livepatch/core.h new file mode 100644 index 0000000000..38209c7361 --- /dev/null +++ b/kernel/livepatch/core.h @@ -0,0 +1,59 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LIVEPATCH_CORE_H +#define _LIVEPATCH_CORE_H + +#include <linux/livepatch.h> + +extern struct mutex klp_mutex; +extern struct list_head klp_patches; + +#define klp_for_each_patch_safe(patch, tmp_patch) \ + list_for_each_entry_safe(patch, tmp_patch, &klp_patches, list) + +#define klp_for_each_patch(patch) \ + list_for_each_entry(patch, &klp_patches, list) + +void klp_free_patch_async(struct klp_patch *patch); +void klp_free_replaced_patches_async(struct klp_patch *new_patch); +void klp_unpatch_replaced_patches(struct klp_patch *new_patch); +void klp_discard_nops(struct klp_patch *new_patch); + +static inline bool klp_is_object_loaded(struct klp_object *obj) +{ + return !obj->name || obj->mod; +} + +static inline int klp_pre_patch_callback(struct klp_object *obj) +{ + int ret = 0; + + if (obj->callbacks.pre_patch) + ret = (*obj->callbacks.pre_patch)(obj); + + obj->callbacks.post_unpatch_enabled = !ret; + + return ret; +} + +static inline void klp_post_patch_callback(struct klp_object *obj) +{ + if (obj->callbacks.post_patch) + (*obj->callbacks.post_patch)(obj); +} + +static inline void klp_pre_unpatch_callback(struct klp_object *obj) +{ + if (obj->callbacks.pre_unpatch) + (*obj->callbacks.pre_unpatch)(obj); +} + +static inline void klp_post_unpatch_callback(struct klp_object *obj) +{ + if (obj->callbacks.post_unpatch_enabled && + obj->callbacks.post_unpatch) + (*obj->callbacks.post_unpatch)(obj); + + obj->callbacks.post_unpatch_enabled = false; +} + +#endif /* _LIVEPATCH_CORE_H */ diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c new file mode 100644 index 0000000000..4152c71507 --- /dev/null +++ b/kernel/livepatch/patch.c @@ -0,0 +1,289 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * patch.c - livepatch patching functions + * + * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> + * Copyright (C) 2014 SUSE + * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com> + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/livepatch.h> +#include <linux/list.h> +#include <linux/ftrace.h> +#include <linux/rculist.h> +#include <linux/slab.h> +#include <linux/bug.h> +#include <linux/printk.h> +#include "core.h" +#include "patch.h" +#include "transition.h" + +static LIST_HEAD(klp_ops); + +struct klp_ops *klp_find_ops(void *old_func) +{ + struct klp_ops *ops; + struct klp_func *func; + + list_for_each_entry(ops, &klp_ops, node) { + func = list_first_entry(&ops->func_stack, struct klp_func, + stack_node); + if (func->old_func == old_func) + return ops; + } + + return NULL; +} + +static void notrace klp_ftrace_handler(unsigned long ip, + unsigned long parent_ip, + struct ftrace_ops *fops, + struct ftrace_regs *fregs) +{ + struct klp_ops *ops; + struct klp_func *func; + int patch_state; + int bit; + + ops = container_of(fops, struct klp_ops, fops); + + /* + * The ftrace_test_recursion_trylock() will disable preemption, + * which is required for the variant of synchronize_rcu() that is + * used to allow patching functions where RCU is not watching. + * See klp_synchronize_transition() for more details. + */ + bit = ftrace_test_recursion_trylock(ip, parent_ip); + if (WARN_ON_ONCE(bit < 0)) + return; + + func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, + stack_node); + + /* + * func should never be NULL because preemption should be disabled here + * and unregister_ftrace_function() does the equivalent of a + * synchronize_rcu() before the func_stack removal. + */ + if (WARN_ON_ONCE(!func)) + goto unlock; + + /* + * In the enable path, enforce the order of the ops->func_stack and + * func->transition reads. The corresponding write barrier is in + * __klp_enable_patch(). + * + * (Note that this barrier technically isn't needed in the disable + * path. In the rare case where klp_update_patch_state() runs before + * this handler, its TIF_PATCH_PENDING read and this func->transition + * read need to be ordered. But klp_update_patch_state() already + * enforces that.) + */ + smp_rmb(); + + if (unlikely(func->transition)) { + + /* + * Enforce the order of the func->transition and + * current->patch_state reads. Otherwise we could read an + * out-of-date task state and pick the wrong function. The + * corresponding write barrier is in klp_init_transition(). + */ + smp_rmb(); + + patch_state = current->patch_state; + + WARN_ON_ONCE(patch_state == KLP_UNDEFINED); + + if (patch_state == KLP_UNPATCHED) { + /* + * Use the previously patched version of the function. + * If no previous patches exist, continue with the + * original function. + */ + func = list_entry_rcu(func->stack_node.next, + struct klp_func, stack_node); + + if (&func->stack_node == &ops->func_stack) + goto unlock; + } + } + + /* + * NOPs are used to replace existing patches with original code. + * Do nothing! Setting pc would cause an infinite loop. + */ + if (func->nop) + goto unlock; + + ftrace_regs_set_instruction_pointer(fregs, (unsigned long)func->new_func); + +unlock: + ftrace_test_recursion_unlock(bit); +} + +static void klp_unpatch_func(struct klp_func *func) +{ + struct klp_ops *ops; + + if (WARN_ON(!func->patched)) + return; + if (WARN_ON(!func->old_func)) + return; + + ops = klp_find_ops(func->old_func); + if (WARN_ON(!ops)) + return; + + if (list_is_singular(&ops->func_stack)) { + unsigned long ftrace_loc; + + ftrace_loc = ftrace_location((unsigned long)func->old_func); + if (WARN_ON(!ftrace_loc)) + return; + + WARN_ON(unregister_ftrace_function(&ops->fops)); + WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0)); + + list_del_rcu(&func->stack_node); + list_del(&ops->node); + kfree(ops); + } else { + list_del_rcu(&func->stack_node); + } + + func->patched = false; +} + +static int klp_patch_func(struct klp_func *func) +{ + struct klp_ops *ops; + int ret; + + if (WARN_ON(!func->old_func)) + return -EINVAL; + + if (WARN_ON(func->patched)) + return -EINVAL; + + ops = klp_find_ops(func->old_func); + if (!ops) { + unsigned long ftrace_loc; + + ftrace_loc = ftrace_location((unsigned long)func->old_func); + if (!ftrace_loc) { + pr_err("failed to find location for function '%s'\n", + func->old_name); + return -EINVAL; + } + + ops = kzalloc(sizeof(*ops), GFP_KERNEL); + if (!ops) + return -ENOMEM; + + ops->fops.func = klp_ftrace_handler; + ops->fops.flags = FTRACE_OPS_FL_DYNAMIC | +#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS + FTRACE_OPS_FL_SAVE_REGS | +#endif + FTRACE_OPS_FL_IPMODIFY | + FTRACE_OPS_FL_PERMANENT; + + list_add(&ops->node, &klp_ops); + + INIT_LIST_HEAD(&ops->func_stack); + list_add_rcu(&func->stack_node, &ops->func_stack); + + ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0); + if (ret) { + pr_err("failed to set ftrace filter for function '%s' (%d)\n", + func->old_name, ret); + goto err; + } + + ret = register_ftrace_function(&ops->fops); + if (ret) { + pr_err("failed to register ftrace handler for function '%s' (%d)\n", + func->old_name, ret); + ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0); + goto err; + } + + + } else { + list_add_rcu(&func->stack_node, &ops->func_stack); + } + + func->patched = true; + + return 0; + +err: + list_del_rcu(&func->stack_node); + list_del(&ops->node); + kfree(ops); + return ret; +} + +static void __klp_unpatch_object(struct klp_object *obj, bool nops_only) +{ + struct klp_func *func; + + klp_for_each_func(obj, func) { + if (nops_only && !func->nop) + continue; + + if (func->patched) + klp_unpatch_func(func); + } + + if (obj->dynamic || !nops_only) + obj->patched = false; +} + + +void klp_unpatch_object(struct klp_object *obj) +{ + __klp_unpatch_object(obj, false); +} + +int klp_patch_object(struct klp_object *obj) +{ + struct klp_func *func; + int ret; + + if (WARN_ON(obj->patched)) + return -EINVAL; + + klp_for_each_func(obj, func) { + ret = klp_patch_func(func); + if (ret) { + klp_unpatch_object(obj); + return ret; + } + } + obj->patched = true; + + return 0; +} + +static void __klp_unpatch_objects(struct klp_patch *patch, bool nops_only) +{ + struct klp_object *obj; + + klp_for_each_object(patch, obj) + if (obj->patched) + __klp_unpatch_object(obj, nops_only); +} + +void klp_unpatch_objects(struct klp_patch *patch) +{ + __klp_unpatch_objects(patch, false); +} + +void klp_unpatch_objects_dynamic(struct klp_patch *patch) +{ + __klp_unpatch_objects(patch, true); +} diff --git a/kernel/livepatch/patch.h b/kernel/livepatch/patch.h new file mode 100644 index 0000000000..d5f2fbe373 --- /dev/null +++ b/kernel/livepatch/patch.h @@ -0,0 +1,35 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LIVEPATCH_PATCH_H +#define _LIVEPATCH_PATCH_H + +#include <linux/livepatch.h> +#include <linux/list.h> +#include <linux/ftrace.h> + +/** + * struct klp_ops - structure for tracking registered ftrace ops structs + * + * A single ftrace_ops is shared between all enabled replacement functions + * (klp_func structs) which have the same old_func. This allows the switch + * between function versions to happen instantaneously by updating the klp_ops + * struct's func_stack list. The winner is the klp_func at the top of the + * func_stack (front of the list). + * + * @node: node for the global klp_ops list + * @func_stack: list head for the stack of klp_func's (active func is on top) + * @fops: registered ftrace ops struct + */ +struct klp_ops { + struct list_head node; + struct list_head func_stack; + struct ftrace_ops fops; +}; + +struct klp_ops *klp_find_ops(void *old_func); + +int klp_patch_object(struct klp_object *obj); +void klp_unpatch_object(struct klp_object *obj); +void klp_unpatch_objects(struct klp_patch *patch); +void klp_unpatch_objects_dynamic(struct klp_patch *patch); + +#endif /* _LIVEPATCH_PATCH_H */ diff --git a/kernel/livepatch/shadow.c b/kernel/livepatch/shadow.c new file mode 100644 index 0000000000..c2e724d97d --- /dev/null +++ b/kernel/livepatch/shadow.c @@ -0,0 +1,299 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * shadow.c - Shadow Variables + * + * Copyright (C) 2014 Josh Poimboeuf <jpoimboe@redhat.com> + * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> + * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com> + */ + +/** + * DOC: Shadow variable API concurrency notes: + * + * The shadow variable API provides a simple relationship between an + * <obj, id> pair and a pointer value. It is the responsibility of the + * caller to provide any mutual exclusion required of the shadow data. + * + * Once a shadow variable is attached to its parent object via the + * klp_shadow_*alloc() API calls, it is considered live: any subsequent + * call to klp_shadow_get() may then return the shadow variable's data + * pointer. Callers of klp_shadow_*alloc() should prepare shadow data + * accordingly. + * + * The klp_shadow_*alloc() API calls may allocate memory for new shadow + * variable structures. Their implementation does not call kmalloc + * inside any spinlocks, but API callers should pass GFP flags according + * to their specific needs. + * + * The klp_shadow_hash is an RCU-enabled hashtable and is safe against + * concurrent klp_shadow_free() and klp_shadow_get() operations. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/hashtable.h> +#include <linux/slab.h> +#include <linux/livepatch.h> + +static DEFINE_HASHTABLE(klp_shadow_hash, 12); + +/* + * klp_shadow_lock provides exclusive access to the klp_shadow_hash and + * the shadow variables it references. + */ +static DEFINE_SPINLOCK(klp_shadow_lock); + +/** + * struct klp_shadow - shadow variable structure + * @node: klp_shadow_hash hash table node + * @rcu_head: RCU is used to safely free this structure + * @obj: pointer to parent object + * @id: data identifier + * @data: data area + */ +struct klp_shadow { + struct hlist_node node; + struct rcu_head rcu_head; + void *obj; + unsigned long id; + char data[]; +}; + +/** + * klp_shadow_match() - verify a shadow variable matches given <obj, id> + * @shadow: shadow variable to match + * @obj: pointer to parent object + * @id: data identifier + * + * Return: true if the shadow variable matches. + */ +static inline bool klp_shadow_match(struct klp_shadow *shadow, void *obj, + unsigned long id) +{ + return shadow->obj == obj && shadow->id == id; +} + +/** + * klp_shadow_get() - retrieve a shadow variable data pointer + * @obj: pointer to parent object + * @id: data identifier + * + * Return: the shadow variable data element, NULL on failure. + */ +void *klp_shadow_get(void *obj, unsigned long id) +{ + struct klp_shadow *shadow; + + rcu_read_lock(); + + hash_for_each_possible_rcu(klp_shadow_hash, shadow, node, + (unsigned long)obj) { + + if (klp_shadow_match(shadow, obj, id)) { + rcu_read_unlock(); + return shadow->data; + } + } + + rcu_read_unlock(); + + return NULL; +} +EXPORT_SYMBOL_GPL(klp_shadow_get); + +static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, + size_t size, gfp_t gfp_flags, + klp_shadow_ctor_t ctor, void *ctor_data, + bool warn_on_exist) +{ + struct klp_shadow *new_shadow; + void *shadow_data; + unsigned long flags; + + /* Check if the shadow variable already exists */ + shadow_data = klp_shadow_get(obj, id); + if (shadow_data) + goto exists; + + /* + * Allocate a new shadow variable. Fill it with zeroes by default. + * More complex setting can be done by @ctor function. But it is + * called only when the buffer is really used (under klp_shadow_lock). + */ + new_shadow = kzalloc(size + sizeof(*new_shadow), gfp_flags); + if (!new_shadow) + return NULL; + + /* Look for <obj, id> again under the lock */ + spin_lock_irqsave(&klp_shadow_lock, flags); + shadow_data = klp_shadow_get(obj, id); + if (unlikely(shadow_data)) { + /* + * Shadow variable was found, throw away speculative + * allocation. + */ + spin_unlock_irqrestore(&klp_shadow_lock, flags); + kfree(new_shadow); + goto exists; + } + + new_shadow->obj = obj; + new_shadow->id = id; + + if (ctor) { + int err; + + err = ctor(obj, new_shadow->data, ctor_data); + if (err) { + spin_unlock_irqrestore(&klp_shadow_lock, flags); + kfree(new_shadow); + pr_err("Failed to construct shadow variable <%p, %lx> (%d)\n", + obj, id, err); + return NULL; + } + } + + /* No <obj, id> found, so attach the newly allocated one */ + hash_add_rcu(klp_shadow_hash, &new_shadow->node, + (unsigned long)new_shadow->obj); + spin_unlock_irqrestore(&klp_shadow_lock, flags); + + return new_shadow->data; + +exists: + if (warn_on_exist) { + WARN(1, "Duplicate shadow variable <%p, %lx>\n", obj, id); + return NULL; + } + + return shadow_data; +} + +/** + * klp_shadow_alloc() - allocate and add a new shadow variable + * @obj: pointer to parent object + * @id: data identifier + * @size: size of attached data + * @gfp_flags: GFP mask for allocation + * @ctor: custom constructor to initialize the shadow data (optional) + * @ctor_data: pointer to any data needed by @ctor (optional) + * + * Allocates @size bytes for new shadow variable data using @gfp_flags. + * The data are zeroed by default. They are further initialized by @ctor + * function if it is not NULL. The new shadow variable is then added + * to the global hashtable. + * + * If an existing <obj, id> shadow variable can be found, this routine will + * issue a WARN, exit early and return NULL. + * + * This function guarantees that the constructor function is called only when + * the variable did not exist before. The cost is that @ctor is called + * in atomic context under a spin lock. + * + * Return: the shadow variable data element, NULL on duplicate or + * failure. + */ +void *klp_shadow_alloc(void *obj, unsigned long id, + size_t size, gfp_t gfp_flags, + klp_shadow_ctor_t ctor, void *ctor_data) +{ + return __klp_shadow_get_or_alloc(obj, id, size, gfp_flags, + ctor, ctor_data, true); +} +EXPORT_SYMBOL_GPL(klp_shadow_alloc); + +/** + * klp_shadow_get_or_alloc() - get existing or allocate a new shadow variable + * @obj: pointer to parent object + * @id: data identifier + * @size: size of attached data + * @gfp_flags: GFP mask for allocation + * @ctor: custom constructor to initialize the shadow data (optional) + * @ctor_data: pointer to any data needed by @ctor (optional) + * + * Returns a pointer to existing shadow data if an <obj, id> shadow + * variable is already present. Otherwise, it creates a new shadow + * variable like klp_shadow_alloc(). + * + * This function guarantees that only one shadow variable exists with the given + * @id for the given @obj. It also guarantees that the constructor function + * will be called only when the variable did not exist before. The cost is + * that @ctor is called in atomic context under a spin lock. + * + * Return: the shadow variable data element, NULL on failure. + */ +void *klp_shadow_get_or_alloc(void *obj, unsigned long id, + size_t size, gfp_t gfp_flags, + klp_shadow_ctor_t ctor, void *ctor_data) +{ + return __klp_shadow_get_or_alloc(obj, id, size, gfp_flags, + ctor, ctor_data, false); +} +EXPORT_SYMBOL_GPL(klp_shadow_get_or_alloc); + +static void klp_shadow_free_struct(struct klp_shadow *shadow, + klp_shadow_dtor_t dtor) +{ + hash_del_rcu(&shadow->node); + if (dtor) + dtor(shadow->obj, shadow->data); + kfree_rcu(shadow, rcu_head); +} + +/** + * klp_shadow_free() - detach and free a <obj, id> shadow variable + * @obj: pointer to parent object + * @id: data identifier + * @dtor: custom callback that can be used to unregister the variable + * and/or free data that the shadow variable points to (optional) + * + * This function releases the memory for this <obj, id> shadow variable + * instance, callers should stop referencing it accordingly. + */ +void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor) +{ + struct klp_shadow *shadow; + unsigned long flags; + + spin_lock_irqsave(&klp_shadow_lock, flags); + + /* Delete <obj, id> from hash */ + hash_for_each_possible(klp_shadow_hash, shadow, node, + (unsigned long)obj) { + + if (klp_shadow_match(shadow, obj, id)) { + klp_shadow_free_struct(shadow, dtor); + break; + } + } + + spin_unlock_irqrestore(&klp_shadow_lock, flags); +} +EXPORT_SYMBOL_GPL(klp_shadow_free); + +/** + * klp_shadow_free_all() - detach and free all <_, id> shadow variables + * @id: data identifier + * @dtor: custom callback that can be used to unregister the variable + * and/or free data that the shadow variable points to (optional) + * + * This function releases the memory for all <_, id> shadow variable + * instances, callers should stop referencing them accordingly. + */ +void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor) +{ + struct klp_shadow *shadow; + unsigned long flags; + int i; + + spin_lock_irqsave(&klp_shadow_lock, flags); + + /* Delete all <_, id> from hash */ + hash_for_each(klp_shadow_hash, i, shadow, node) { + if (klp_shadow_match(shadow, shadow->obj, id)) + klp_shadow_free_struct(shadow, dtor); + } + + spin_unlock_irqrestore(&klp_shadow_lock, flags); +} +EXPORT_SYMBOL_GPL(klp_shadow_free_all); diff --git a/kernel/livepatch/state.c b/kernel/livepatch/state.c new file mode 100644 index 0000000000..2565d039ad --- /dev/null +++ b/kernel/livepatch/state.c @@ -0,0 +1,119 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * system_state.c - State of the system modified by livepatches + * + * Copyright (C) 2019 SUSE + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/livepatch.h> +#include "core.h" +#include "state.h" +#include "transition.h" + +#define klp_for_each_state(patch, state) \ + for (state = patch->states; state && state->id; state++) + +/** + * klp_get_state() - get information about system state modified by + * the given patch + * @patch: livepatch that modifies the given system state + * @id: custom identifier of the modified system state + * + * Checks whether the given patch modifies the given system state. + * + * The function can be called either from pre/post (un)patch + * callbacks or from the kernel code added by the livepatch. + * + * Return: pointer to struct klp_state when found, otherwise NULL. + */ +struct klp_state *klp_get_state(struct klp_patch *patch, unsigned long id) +{ + struct klp_state *state; + + klp_for_each_state(patch, state) { + if (state->id == id) + return state; + } + + return NULL; +} +EXPORT_SYMBOL_GPL(klp_get_state); + +/** + * klp_get_prev_state() - get information about system state modified by + * the already installed livepatches + * @id: custom identifier of the modified system state + * + * Checks whether already installed livepatches modify the given + * system state. + * + * The same system state can be modified by more non-cumulative + * livepatches. It is expected that the latest livepatch has + * the most up-to-date information. + * + * The function can be called only during transition when a new + * livepatch is being enabled or when such a transition is reverted. + * It is typically called only from pre/post (un)patch + * callbacks. + * + * Return: pointer to the latest struct klp_state from already + * installed livepatches, NULL when not found. + */ +struct klp_state *klp_get_prev_state(unsigned long id) +{ + struct klp_patch *patch; + struct klp_state *state, *last_state = NULL; + + if (WARN_ON_ONCE(!klp_transition_patch)) + return NULL; + + klp_for_each_patch(patch) { + if (patch == klp_transition_patch) + goto out; + + state = klp_get_state(patch, id); + if (state) + last_state = state; + } + +out: + return last_state; +} +EXPORT_SYMBOL_GPL(klp_get_prev_state); + +/* Check if the patch is able to deal with the existing system state. */ +static bool klp_is_state_compatible(struct klp_patch *patch, + struct klp_state *old_state) +{ + struct klp_state *state; + + state = klp_get_state(patch, old_state->id); + + /* A cumulative livepatch must handle all already modified states. */ + if (!state) + return !patch->replace; + + return state->version >= old_state->version; +} + +/* + * Check that the new livepatch will not break the existing system states. + * Cumulative patches must handle all already modified states. + * Non-cumulative patches can touch already modified states. + */ +bool klp_is_patch_compatible(struct klp_patch *patch) +{ + struct klp_patch *old_patch; + struct klp_state *old_state; + + klp_for_each_patch(old_patch) { + klp_for_each_state(old_patch, old_state) { + if (!klp_is_state_compatible(patch, old_state)) + return false; + } + } + + return true; +} diff --git a/kernel/livepatch/state.h b/kernel/livepatch/state.h new file mode 100644 index 0000000000..49d9c16e87 --- /dev/null +++ b/kernel/livepatch/state.h @@ -0,0 +1,9 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LIVEPATCH_STATE_H +#define _LIVEPATCH_STATE_H + +#include <linux/livepatch.h> + +bool klp_is_patch_compatible(struct klp_patch *patch); + +#endif /* _LIVEPATCH_STATE_H */ diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c new file mode 100644 index 0000000000..e54c3d60a9 --- /dev/null +++ b/kernel/livepatch/transition.c @@ -0,0 +1,752 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * transition.c - Kernel Live Patching transition functions + * + * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com> + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/cpu.h> +#include <linux/stacktrace.h> +#include <linux/static_call.h> +#include "core.h" +#include "patch.h" +#include "transition.h" + +#define MAX_STACK_ENTRIES 100 +static DEFINE_PER_CPU(unsigned long[MAX_STACK_ENTRIES], klp_stack_entries); + +#define STACK_ERR_BUF_SIZE 128 + +#define SIGNALS_TIMEOUT 15 + +struct klp_patch *klp_transition_patch; + +static int klp_target_state = KLP_UNDEFINED; + +static unsigned int klp_signals_cnt; + +/* + * When a livepatch is in progress, enable klp stack checking in + * cond_resched(). This helps CPU-bound kthreads get patched. + */ +#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL) + +#define klp_cond_resched_enable() sched_dynamic_klp_enable() +#define klp_cond_resched_disable() sched_dynamic_klp_disable() + +#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */ + +DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key); +EXPORT_SYMBOL(klp_sched_try_switch_key); + +#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key) +#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key) + +#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */ + +/* + * This work can be performed periodically to finish patching or unpatching any + * "straggler" tasks which failed to transition in the first attempt. + */ +static void klp_transition_work_fn(struct work_struct *work) +{ + mutex_lock(&klp_mutex); + + if (klp_transition_patch) + klp_try_complete_transition(); + + mutex_unlock(&klp_mutex); +} +static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn); + +/* + * This function is just a stub to implement a hard force + * of synchronize_rcu(). This requires synchronizing + * tasks even in userspace and idle. + */ +static void klp_sync(struct work_struct *work) +{ +} + +/* + * We allow to patch also functions where RCU is not watching, + * e.g. before user_exit(). We can not rely on the RCU infrastructure + * to do the synchronization. Instead hard force the sched synchronization. + * + * This approach allows to use RCU functions for manipulating func_stack + * safely. + */ +static void klp_synchronize_transition(void) +{ + schedule_on_each_cpu(klp_sync); +} + +/* + * The transition to the target patch state is complete. Clean up the data + * structures. + */ +static void klp_complete_transition(void) +{ + struct klp_object *obj; + struct klp_func *func; + struct task_struct *g, *task; + unsigned int cpu; + + pr_debug("'%s': completing %s transition\n", + klp_transition_patch->mod->name, + klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); + + if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) { + klp_unpatch_replaced_patches(klp_transition_patch); + klp_discard_nops(klp_transition_patch); + } + + if (klp_target_state == KLP_UNPATCHED) { + /* + * All tasks have transitioned to KLP_UNPATCHED so we can now + * remove the new functions from the func_stack. + */ + klp_unpatch_objects(klp_transition_patch); + + /* + * Make sure klp_ftrace_handler() can no longer see functions + * from this patch on the ops->func_stack. Otherwise, after + * func->transition gets cleared, the handler may choose a + * removed function. + */ + klp_synchronize_transition(); + } + + klp_for_each_object(klp_transition_patch, obj) + klp_for_each_func(obj, func) + func->transition = false; + + /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ + if (klp_target_state == KLP_PATCHED) + klp_synchronize_transition(); + + read_lock(&tasklist_lock); + for_each_process_thread(g, task) { + WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); + task->patch_state = KLP_UNDEFINED; + } + read_unlock(&tasklist_lock); + + for_each_possible_cpu(cpu) { + task = idle_task(cpu); + WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); + task->patch_state = KLP_UNDEFINED; + } + + klp_for_each_object(klp_transition_patch, obj) { + if (!klp_is_object_loaded(obj)) + continue; + if (klp_target_state == KLP_PATCHED) + klp_post_patch_callback(obj); + else if (klp_target_state == KLP_UNPATCHED) + klp_post_unpatch_callback(obj); + } + + pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name, + klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); + + klp_target_state = KLP_UNDEFINED; + klp_transition_patch = NULL; +} + +/* + * This is called in the error path, to cancel a transition before it has + * started, i.e. klp_init_transition() has been called but + * klp_start_transition() hasn't. If the transition *has* been started, + * klp_reverse_transition() should be used instead. + */ +void klp_cancel_transition(void) +{ + if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED)) + return; + + pr_debug("'%s': canceling patching transition, going to unpatch\n", + klp_transition_patch->mod->name); + + klp_target_state = KLP_UNPATCHED; + klp_complete_transition(); +} + +/* + * Switch the patched state of the task to the set of functions in the target + * patch state. + * + * NOTE: If task is not 'current', the caller must ensure the task is inactive. + * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value. + */ +void klp_update_patch_state(struct task_struct *task) +{ + /* + * A variant of synchronize_rcu() is used to allow patching functions + * where RCU is not watching, see klp_synchronize_transition(). + */ + preempt_disable_notrace(); + + /* + * This test_and_clear_tsk_thread_flag() call also serves as a read + * barrier (smp_rmb) for two cases: + * + * 1) Enforce the order of the TIF_PATCH_PENDING read and the + * klp_target_state read. The corresponding write barriers are in + * klp_init_transition() and klp_reverse_transition(). + * + * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read + * of func->transition, if klp_ftrace_handler() is called later on + * the same CPU. See __klp_disable_patch(). + */ + if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING)) + task->patch_state = READ_ONCE(klp_target_state); + + preempt_enable_notrace(); +} + +/* + * Determine whether the given stack trace includes any references to a + * to-be-patched or to-be-unpatched function. + */ +static int klp_check_stack_func(struct klp_func *func, unsigned long *entries, + unsigned int nr_entries) +{ + unsigned long func_addr, func_size, address; + struct klp_ops *ops; + int i; + + if (klp_target_state == KLP_UNPATCHED) { + /* + * Check for the to-be-unpatched function + * (the func itself). + */ + func_addr = (unsigned long)func->new_func; + func_size = func->new_size; + } else { + /* + * Check for the to-be-patched function + * (the previous func). + */ + ops = klp_find_ops(func->old_func); + + if (list_is_singular(&ops->func_stack)) { + /* original function */ + func_addr = (unsigned long)func->old_func; + func_size = func->old_size; + } else { + /* previously patched function */ + struct klp_func *prev; + + prev = list_next_entry(func, stack_node); + func_addr = (unsigned long)prev->new_func; + func_size = prev->new_size; + } + } + + for (i = 0; i < nr_entries; i++) { + address = entries[i]; + + if (address >= func_addr && address < func_addr + func_size) + return -EAGAIN; + } + + return 0; +} + +/* + * Determine whether it's safe to transition the task to the target patch state + * by looking for any to-be-patched or to-be-unpatched functions on its stack. + */ +static int klp_check_stack(struct task_struct *task, const char **oldname) +{ + unsigned long *entries = this_cpu_ptr(klp_stack_entries); + struct klp_object *obj; + struct klp_func *func; + int ret, nr_entries; + + /* Protect 'klp_stack_entries' */ + lockdep_assert_preemption_disabled(); + + ret = stack_trace_save_tsk_reliable(task, entries, MAX_STACK_ENTRIES); + if (ret < 0) + return -EINVAL; + nr_entries = ret; + + klp_for_each_object(klp_transition_patch, obj) { + if (!obj->patched) + continue; + klp_for_each_func(obj, func) { + ret = klp_check_stack_func(func, entries, nr_entries); + if (ret) { + *oldname = func->old_name; + return -EADDRINUSE; + } + } + } + + return 0; +} + +static int klp_check_and_switch_task(struct task_struct *task, void *arg) +{ + int ret; + + if (task_curr(task) && task != current) + return -EBUSY; + + ret = klp_check_stack(task, arg); + if (ret) + return ret; + + clear_tsk_thread_flag(task, TIF_PATCH_PENDING); + task->patch_state = klp_target_state; + return 0; +} + +/* + * Try to safely switch a task to the target patch state. If it's currently + * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or + * if the stack is unreliable, return false. + */ +static bool klp_try_switch_task(struct task_struct *task) +{ + const char *old_name; + int ret; + + /* check if this task has already switched over */ + if (task->patch_state == klp_target_state) + return true; + + /* + * For arches which don't have reliable stack traces, we have to rely + * on other methods (e.g., switching tasks at kernel exit). + */ + if (!klp_have_reliable_stack()) + return false; + + /* + * Now try to check the stack for any to-be-patched or to-be-unpatched + * functions. If all goes well, switch the task to the target patch + * state. + */ + if (task == current) + ret = klp_check_and_switch_task(current, &old_name); + else + ret = task_call_func(task, klp_check_and_switch_task, &old_name); + + switch (ret) { + case 0: /* success */ + break; + + case -EBUSY: /* klp_check_and_switch_task() */ + pr_debug("%s: %s:%d is running\n", + __func__, task->comm, task->pid); + break; + case -EINVAL: /* klp_check_and_switch_task() */ + pr_debug("%s: %s:%d has an unreliable stack\n", + __func__, task->comm, task->pid); + break; + case -EADDRINUSE: /* klp_check_and_switch_task() */ + pr_debug("%s: %s:%d is sleeping on function %s\n", + __func__, task->comm, task->pid, old_name); + break; + + default: + pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n", + __func__, ret, task->comm, task->pid); + break; + } + + return !ret; +} + +void __klp_sched_try_switch(void) +{ + if (likely(!klp_patch_pending(current))) + return; + + /* + * This function is called from cond_resched() which is called in many + * places throughout the kernel. Using the klp_mutex here might + * deadlock. + * + * Instead, disable preemption to prevent racing with other callers of + * klp_try_switch_task(). Thanks to task_call_func() they won't be + * able to switch this task while it's running. + */ + preempt_disable(); + + /* + * Make sure current didn't get patched between the above check and + * preempt_disable(). + */ + if (unlikely(!klp_patch_pending(current))) + goto out; + + /* + * Enforce the order of the TIF_PATCH_PENDING read above and the + * klp_target_state read in klp_try_switch_task(). The corresponding + * write barriers are in klp_init_transition() and + * klp_reverse_transition(). + */ + smp_rmb(); + + klp_try_switch_task(current); + +out: + preempt_enable(); +} +EXPORT_SYMBOL(__klp_sched_try_switch); + +/* + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. + * Kthreads with TIF_PATCH_PENDING set are woken up. + */ +static void klp_send_signals(void) +{ + struct task_struct *g, *task; + + if (klp_signals_cnt == SIGNALS_TIMEOUT) + pr_notice("signaling remaining tasks\n"); + + read_lock(&tasklist_lock); + for_each_process_thread(g, task) { + if (!klp_patch_pending(task)) + continue; + + /* + * There is a small race here. We could see TIF_PATCH_PENDING + * set and decide to wake up a kthread or send a fake signal. + * Meanwhile the task could migrate itself and the action + * would be meaningless. It is not serious though. + */ + if (task->flags & PF_KTHREAD) { + /* + * Wake up a kthread which sleeps interruptedly and + * still has not been migrated. + */ + wake_up_state(task, TASK_INTERRUPTIBLE); + } else { + /* + * Send fake signal to all non-kthread tasks which are + * still not migrated. + */ + set_notify_signal(task); + } + } + read_unlock(&tasklist_lock); +} + +/* + * Try to switch all remaining tasks to the target patch state by walking the + * stacks of sleeping tasks and looking for any to-be-patched or + * to-be-unpatched functions. If such functions are found, the task can't be + * switched yet. + * + * If any tasks are still stuck in the initial patch state, schedule a retry. + */ +void klp_try_complete_transition(void) +{ + unsigned int cpu; + struct task_struct *g, *task; + struct klp_patch *patch; + bool complete = true; + + WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); + + /* + * Try to switch the tasks to the target patch state by walking their + * stacks and looking for any to-be-patched or to-be-unpatched + * functions. If such functions are found on a stack, or if the stack + * is deemed unreliable, the task can't be switched yet. + * + * Usually this will transition most (or all) of the tasks on a system + * unless the patch includes changes to a very common function. + */ + read_lock(&tasklist_lock); + for_each_process_thread(g, task) + if (!klp_try_switch_task(task)) + complete = false; + read_unlock(&tasklist_lock); + + /* + * Ditto for the idle "swapper" tasks. + */ + cpus_read_lock(); + for_each_possible_cpu(cpu) { + task = idle_task(cpu); + if (cpu_online(cpu)) { + if (!klp_try_switch_task(task)) { + complete = false; + /* Make idle task go through the main loop. */ + wake_up_if_idle(cpu); + } + } else if (task->patch_state != klp_target_state) { + /* offline idle tasks can be switched immediately */ + clear_tsk_thread_flag(task, TIF_PATCH_PENDING); + task->patch_state = klp_target_state; + } + } + cpus_read_unlock(); + + if (!complete) { + if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT)) + klp_send_signals(); + klp_signals_cnt++; + + /* + * Some tasks weren't able to be switched over. Try again + * later and/or wait for other methods like kernel exit + * switching. + */ + schedule_delayed_work(&klp_transition_work, + round_jiffies_relative(HZ)); + return; + } + + /* Done! Now cleanup the data structures. */ + klp_cond_resched_disable(); + patch = klp_transition_patch; + klp_complete_transition(); + + /* + * It would make more sense to free the unused patches in + * klp_complete_transition() but it is called also + * from klp_cancel_transition(). + */ + if (!patch->enabled) + klp_free_patch_async(patch); + else if (patch->replace) + klp_free_replaced_patches_async(patch); +} + +/* + * Start the transition to the specified target patch state so tasks can begin + * switching to it. + */ +void klp_start_transition(void) +{ + struct task_struct *g, *task; + unsigned int cpu; + + WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); + + pr_notice("'%s': starting %s transition\n", + klp_transition_patch->mod->name, + klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); + + /* + * Mark all normal tasks as needing a patch state update. They'll + * switch either in klp_try_complete_transition() or as they exit the + * kernel. + */ + read_lock(&tasklist_lock); + for_each_process_thread(g, task) + if (task->patch_state != klp_target_state) + set_tsk_thread_flag(task, TIF_PATCH_PENDING); + read_unlock(&tasklist_lock); + + /* + * Mark all idle tasks as needing a patch state update. They'll switch + * either in klp_try_complete_transition() or at the idle loop switch + * point. + */ + for_each_possible_cpu(cpu) { + task = idle_task(cpu); + if (task->patch_state != klp_target_state) + set_tsk_thread_flag(task, TIF_PATCH_PENDING); + } + + klp_cond_resched_enable(); + + klp_signals_cnt = 0; +} + +/* + * Initialize the global target patch state and all tasks to the initial patch + * state, and initialize all function transition states to true in preparation + * for patching or unpatching. + */ +void klp_init_transition(struct klp_patch *patch, int state) +{ + struct task_struct *g, *task; + unsigned int cpu; + struct klp_object *obj; + struct klp_func *func; + int initial_state = !state; + + WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED); + + klp_transition_patch = patch; + + /* + * Set the global target patch state which tasks will switch to. This + * has no effect until the TIF_PATCH_PENDING flags get set later. + */ + klp_target_state = state; + + pr_debug("'%s': initializing %s transition\n", patch->mod->name, + klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); + + /* + * Initialize all tasks to the initial patch state to prepare them for + * switching to the target state. + */ + read_lock(&tasklist_lock); + for_each_process_thread(g, task) { + WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); + task->patch_state = initial_state; + } + read_unlock(&tasklist_lock); + + /* + * Ditto for the idle "swapper" tasks. + */ + for_each_possible_cpu(cpu) { + task = idle_task(cpu); + WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED); + task->patch_state = initial_state; + } + + /* + * Enforce the order of the task->patch_state initializations and the + * func->transition updates to ensure that klp_ftrace_handler() doesn't + * see a func in transition with a task->patch_state of KLP_UNDEFINED. + * + * Also enforce the order of the klp_target_state write and future + * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and + * __klp_sched_try_switch() don't set a task->patch_state to + * KLP_UNDEFINED. + */ + smp_wmb(); + + /* + * Set the func transition states so klp_ftrace_handler() will know to + * switch to the transition logic. + * + * When patching, the funcs aren't yet in the func_stack and will be + * made visible to the ftrace handler shortly by the calls to + * klp_patch_object(). + * + * When unpatching, the funcs are already in the func_stack and so are + * already visible to the ftrace handler. + */ + klp_for_each_object(patch, obj) + klp_for_each_func(obj, func) + func->transition = true; +} + +/* + * This function can be called in the middle of an existing transition to + * reverse the direction of the target patch state. This can be done to + * effectively cancel an existing enable or disable operation if there are any + * tasks which are stuck in the initial patch state. + */ +void klp_reverse_transition(void) +{ + unsigned int cpu; + struct task_struct *g, *task; + + pr_debug("'%s': reversing transition from %s\n", + klp_transition_patch->mod->name, + klp_target_state == KLP_PATCHED ? "patching to unpatching" : + "unpatching to patching"); + + /* + * Clear all TIF_PATCH_PENDING flags to prevent races caused by + * klp_update_patch_state() or __klp_sched_try_switch() running in + * parallel with the reverse transition. + */ + read_lock(&tasklist_lock); + for_each_process_thread(g, task) + clear_tsk_thread_flag(task, TIF_PATCH_PENDING); + read_unlock(&tasklist_lock); + + for_each_possible_cpu(cpu) + clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING); + + /* + * Make sure all existing invocations of klp_update_patch_state() and + * __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before + * starting the reverse transition. + */ + klp_synchronize_transition(); + + /* + * All patching has stopped, now re-initialize the global variables to + * prepare for the reverse transition. + */ + klp_transition_patch->enabled = !klp_transition_patch->enabled; + klp_target_state = !klp_target_state; + + /* + * Enforce the order of the klp_target_state write and the + * TIF_PATCH_PENDING writes in klp_start_transition() to ensure + * klp_update_patch_state() and __klp_sched_try_switch() don't set + * task->patch_state to the wrong value. + */ + smp_wmb(); + + klp_start_transition(); +} + +/* Called from copy_process() during fork */ +void klp_copy_process(struct task_struct *child) +{ + + /* + * The parent process may have gone through a KLP transition since + * the thread flag was copied in setup_thread_stack earlier. Bring + * the task flag up to date with the parent here. + * + * The operation is serialized against all klp_*_transition() + * operations by the tasklist_lock. The only exceptions are + * klp_update_patch_state(current) and __klp_sched_try_switch(), but we + * cannot race with them because we are current. + */ + if (test_tsk_thread_flag(current, TIF_PATCH_PENDING)) + set_tsk_thread_flag(child, TIF_PATCH_PENDING); + else + clear_tsk_thread_flag(child, TIF_PATCH_PENDING); + + child->patch_state = current->patch_state; +} + +/* + * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an + * existing transition to finish. + * + * NOTE: klp_update_patch_state(task) requires the task to be inactive or + * 'current'. This is not the case here and the consistency model could be + * broken. Administrator, who is the only one to execute the + * klp_force_transitions(), has to be aware of this. + */ +void klp_force_transition(void) +{ + struct klp_patch *patch; + struct task_struct *g, *task; + unsigned int cpu; + + pr_warn("forcing remaining tasks to the patched state\n"); + + read_lock(&tasklist_lock); + for_each_process_thread(g, task) + klp_update_patch_state(task); + read_unlock(&tasklist_lock); + + for_each_possible_cpu(cpu) + klp_update_patch_state(idle_task(cpu)); + + /* Set forced flag for patches being removed. */ + if (klp_target_state == KLP_UNPATCHED) + klp_transition_patch->forced = true; + else if (klp_transition_patch->replace) { + klp_for_each_patch(patch) { + if (patch != klp_transition_patch) + patch->forced = true; + } + } +} diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h new file mode 100644 index 0000000000..322db16233 --- /dev/null +++ b/kernel/livepatch/transition.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LIVEPATCH_TRANSITION_H +#define _LIVEPATCH_TRANSITION_H + +#include <linux/livepatch.h> + +extern struct klp_patch *klp_transition_patch; + +void klp_init_transition(struct klp_patch *patch, int state); +void klp_cancel_transition(void); +void klp_start_transition(void); +void klp_try_complete_transition(void); +void klp_reverse_transition(void); +void klp_force_transition(void); + +#endif /* _LIVEPATCH_TRANSITION_H */ |