3.3.2 Required name format
3.3.3 Example livepatch symbol names
3.3.4 Example `readelf --symbols` output
-4. Symbol table and Elf section access
+4. Architecture-specific sections
+5. Symbol table and Elf section access
----------------------------
0. Background and motivation
Since apply_relocate_add() requires access to a module's section header
table, symbol table, and relocation section indices, Elf information is
-preserved for livepatch modules (see section 4). Livepatch manages its own
+preserved for livepatch modules (see section 5). Livepatch manages its own
relocation sections and symbols, which are described in this document. The
Elf constants used to mark livepatch symbols and relocation sections were
selected from OS-specific ranges according to the definitions from glibc.
sections, as in the case of the sample livepatch module (see
samples/livepatch).
-Since Elf information is preserved for livepatch modules (see Section 4), a
+Since Elf information is preserved for livepatch modules (see Section 5), a
livepatch relocation section can be applied simply by passing in the
appropriate section index to apply_relocate_add(), which then uses it to
access the relocation section and apply the relocations.
[*] Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
"OS" means OS-specific.
+---------------------------------
+4. Architecture-specific sections
+---------------------------------
+Architectures may override arch_klp_init_object_loaded() to perform
+additional arch-specific tasks when a target module loads, such as applying
+arch-specific sections. On x86 for example, we must apply per-object
+.altinstructions and .parainstructions sections when a target module loads.
+These sections must be prefixed with ".klp.arch.$objname." so that they can
+be easily identified when iterating through a patch module's Elf sections
+(See arch/x86/kernel/livepatch.c for a complete example).
+
--------------------------------------
-4. Symbol table and Elf section access
+5. Symbol table and Elf section access
--------------------------------------
A livepatch module's symbol table is accessible through module->symtab.
obj-y += apic/
obj-$(CONFIG_X86_REBOOTFIXUPS) += reboot_fixups_32.o
obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o
+obj-$(CONFIG_LIVEPATCH) += livepatch.o
obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
obj-$(CONFIG_FTRACE_SYSCALLS) += ftrace.o
obj-$(CONFIG_X86_TSC) += trace_clock.o
--- /dev/null
+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * 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/kallsyms.h>
+#include <linux/livepatch.h>
+#include <asm/text-patching.h>
+
+/* Apply per-object alternatives. Based on x86 module_finalize() */
+void arch_klp_init_object_loaded(struct klp_patch *patch,
+ struct klp_object *obj)
+{
+ int cnt;
+ struct klp_modinfo *info;
+ Elf_Shdr *s, *alt = NULL, *para = NULL;
+ void *aseg, *pseg;
+ const char *objname;
+ char sec_objname[MODULE_NAME_LEN];
+ char secname[KSYM_NAME_LEN];
+
+ info = patch->mod->klp_info;
+ objname = obj->name ? obj->name : "vmlinux";
+
+ /* See livepatch core code for BUILD_BUG_ON() explanation */
+ BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
+
+ for (s = info->sechdrs; s < info->sechdrs + info->hdr.e_shnum; s++) {
+ /* Apply per-object .klp.arch sections */
+ cnt = sscanf(info->secstrings + s->sh_name,
+ ".klp.arch.%55[^.].%127s",
+ sec_objname, secname);
+ if (cnt != 2)
+ continue;
+ if (strcmp(sec_objname, objname))
+ continue;
+ if (!strcmp(".altinstructions", secname))
+ alt = s;
+ if (!strcmp(".parainstructions", secname))
+ para = s;
+ }
+
+ if (alt) {
+ aseg = (void *) alt->sh_addr;
+ apply_alternatives(aseg, aseg + alt->sh_size);
+ }
+
+ if (para) {
+ pseg = (void *) para->sh_addr;
+ apply_paravirt(pseg, pseg + para->sh_size);
+ }
+}
int klp_enable_patch(struct klp_patch *);
int klp_disable_patch(struct klp_patch *);
+void arch_klp_init_object_loaded(struct klp_patch *patch,
+ struct klp_object *obj);
+
/* Called from the module loader during module coming/going states */
int klp_module_coming(struct module *mod);
void klp_module_going(struct module *mod);
objname = klp_is_module(obj) ? obj->name : "vmlinux";
- module_disable_ro(pmod);
/* For each klp relocation section */
for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
sec = pmod->klp_info->sechdrs + i;
break;
}
- module_enable_ro(pmod, true);
return ret;
}
list_prev_entry(patch, list)->state == KLP_DISABLED)
return -EBUSY;
- 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);
klp_for_each_object(patch, obj) {
func->old_sympos ? func->old_sympos : 1);
}
+/* Arches may override this to finish any remaining arch-specific tasks */
+void __weak arch_klp_init_object_loaded(struct klp_patch *patch,
+ struct klp_object *obj)
+{
+}
+
/* 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;
+ module_disable_ro(patch->mod);
ret = klp_write_object_relocations(patch->mod, obj);
- if (ret)
+ if (ret) {
+ module_enable_ro(patch->mod, true);
return ret;
+ }
+
+ arch_klp_init_object_loaded(patch, obj);
+ module_enable_ro(patch->mod, true);
klp_for_each_func(obj, func) {
ret = klp_find_object_symbol(obj->name, func->old_name,
buf[l++] = 'C';
if (mod->taints & (1 << TAINT_UNSIGNED_MODULE))
buf[l++] = 'E';
+ if (mod->taints & (1 << TAINT_LIVEPATCH))
+ buf[l++] = 'K';
/*
* TAINT_FORCED_RMMOD: could be added.
* TAINT_CPU_OUT_OF_SPEC, TAINT_MACHINE_CHECK, TAINT_BAD_PAGE don't
}
#ifdef CONFIG_LIVEPATCH
-static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
+static int check_modinfo_livepatch(struct module *mod, struct load_info *info)
{
- mod->klp = get_modinfo(info, "livepatch") ? true : false;
+ if (get_modinfo(info, "livepatch")) {
+ mod->klp = true;
+ add_taint_module(mod, TAINT_LIVEPATCH, LOCKDEP_STILL_OK);
+ }
return 0;
}
#else /* !CONFIG_LIVEPATCH */
-static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
+static int check_modinfo_livepatch(struct module *mod, struct load_info *info)
{
if (get_modinfo(info, "livepatch")) {
pr_err("%s: module is marked as livepatch module, but livepatch support is disabled",
"is unknown, you have been warned.\n", mod->name);
}
- err = find_livepatch_modinfo(mod, info);
+ err = check_modinfo_livepatch(mod, info);
if (err)
return err;
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