livepatch: reuse module loader code to write relocations
Reuse module loader code to write relocations, thereby eliminating the need for architecture specific relocation code in livepatch. Specifically, reuse the apply_relocate_add() function in the module loader to write relocations instead of duplicating functionality in livepatch's arch-dependent klp_write_module_reloc() function. In order to accomplish this, livepatch modules manage their own relocation sections (marked with the SHF_RELA_LIVEPATCH section flag) and livepatch-specific symbols (marked with SHN_LIVEPATCH symbol section index). To apply livepatch relocation sections, livepatch symbols referenced by relocs are resolved and then apply_relocate_add() is called to apply those relocations. In addition, remove x86 livepatch relocation code and the s390 klp_write_module_reloc() function stub. They are no longer needed since relocation work has been offloaded to module loader. Lastly, mark the module as a livepatch module so that the module loader canappropriately identify and initialize it. Signed-off-by: Jessica Yu <jeyu@redhat.com> Reviewed-by: Miroslav Benes <mbenes@suse.cz> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> # for s390 changes Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Jessica Yu
Jiri Kosina
@@ -28,6 +28,8 @@
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#include <linux/list.h>
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#include <linux/kallsyms.h>
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#include <linux/livepatch.h>
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#include <linux/elf.h>
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#include <linux/moduleloader.h>
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#include <asm/cacheflush.h>
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/**
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@@ -204,75 +206,109 @@ static int klp_find_object_symbol(const char *objname, const char *name,
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return -EINVAL;
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}
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/*
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* external symbols are located outside the parent object (where the parent
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* object is either vmlinux or the kmod being patched).
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*/
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static int klp_find_external_symbol(struct module *pmod, const char *name,
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unsigned long *addr)
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static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
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{
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const struct kernel_symbol *sym;
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/* first, check if it's an exported symbol */
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preempt_disable();
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sym = find_symbol(name, NULL, NULL, true, true);
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if (sym) {
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*addr = sym->value;
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preempt_enable();
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return 0;
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}
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preempt_enable();
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int i, cnt, vmlinux, ret;
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char objname[MODULE_NAME_LEN];
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char symname[KSYM_NAME_LEN];
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char *strtab = pmod->core_kallsyms.strtab;
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Elf_Rela *relas;
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Elf_Sym *sym;
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unsigned long sympos, addr;
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/*
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* Check if it's in another .o within the patch module. This also
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* checks that the external symbol is unique.
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* Since the field widths for objname and symname in the sscanf()
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* call are hard-coded and correspond to MODULE_NAME_LEN and
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* KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
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* and KSYM_NAME_LEN have the values we expect them to have.
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*
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* Because the value of MODULE_NAME_LEN can differ among architectures,
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* we use the smallest/strictest upper bound possible (56, based on
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* the current definition of MODULE_NAME_LEN) to prevent overflows.
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*/
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return klp_find_object_symbol(pmod->name, name, 0, addr);
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BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
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relas = (Elf_Rela *) relasec->sh_addr;
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/* For each rela in this klp relocation section */
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for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
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sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
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if (sym->st_shndx != SHN_LIVEPATCH) {
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pr_err("symbol %s is not marked as a livepatch symbol",
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strtab + sym->st_name);
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return -EINVAL;
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}
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/* Format: .klp.sym.objname.symname,sympos */
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cnt = sscanf(strtab + sym->st_name,
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".klp.sym.%55[^.].%127[^,],%lu",
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objname, symname, &sympos);
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if (cnt != 3) {
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pr_err("symbol %s has an incorrectly formatted name",
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strtab + sym->st_name);
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return -EINVAL;
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}
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/* klp_find_object_symbol() treats a NULL objname as vmlinux */
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vmlinux = !strcmp(objname, "vmlinux");
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ret = klp_find_object_symbol(vmlinux ? NULL : objname,
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symname, sympos, &addr);
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if (ret)
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return ret;
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sym->st_value = addr;
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}
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return 0;
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}
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static int klp_write_object_relocations(struct module *pmod,
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struct klp_object *obj)
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{
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int ret = 0;
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unsigned long val;
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struct klp_reloc *reloc;
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int i, cnt, ret = 0;
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const char *objname, *secname;
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char sec_objname[MODULE_NAME_LEN];
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Elf_Shdr *sec;
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if (WARN_ON(!klp_is_object_loaded(obj)))
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return -EINVAL;
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if (WARN_ON(!obj->relocs))
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return -EINVAL;
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objname = klp_is_module(obj) ? obj->name : "vmlinux";
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module_disable_ro(pmod);
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/* For each klp relocation section */
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for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
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sec = pmod->klp_info->sechdrs + i;
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secname = pmod->klp_info->secstrings + sec->sh_name;
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if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
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continue;
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for (reloc = obj->relocs; reloc->name; reloc++) {
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/* discover the address of the referenced symbol */
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if (reloc->external) {
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if (reloc->sympos > 0) {
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pr_err("non-zero sympos for external reloc symbol '%s' is not supported\n",
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reloc->name);
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ret = -EINVAL;
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goto out;
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}
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ret = klp_find_external_symbol(pmod, reloc->name, &val);
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} else
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ret = klp_find_object_symbol(obj->name,
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reloc->name,
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reloc->sympos,
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&val);
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if (ret)
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goto out;
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ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
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val + reloc->addend);
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if (ret) {
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pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
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reloc->name, val, ret);
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goto out;
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/*
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* Format: .klp.rela.sec_objname.section_name
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* See comment in klp_resolve_symbols() for an explanation
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* of the selected field width value.
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*/
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cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
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if (cnt != 1) {
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pr_err("section %s has an incorrectly formatted name",
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secname);
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ret = -EINVAL;
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break;
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}
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if (strcmp(objname, sec_objname))
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continue;
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ret = klp_resolve_symbols(sec, pmod);
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if (ret)
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break;
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ret = apply_relocate_add(pmod->klp_info->sechdrs,
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pmod->core_kallsyms.strtab,
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pmod->klp_info->symndx, i, pmod);
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if (ret)
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break;
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}
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out:
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module_enable_ro(pmod);
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return ret;
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}
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@@ -703,11 +739,9 @@ static int klp_init_object_loaded(struct klp_patch *patch,
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struct klp_func *func;
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int ret;
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if (obj->relocs) {
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ret = klp_write_object_relocations(patch->mod, obj);
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if (ret)
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return ret;
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}
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ret = klp_write_object_relocations(patch->mod, obj);
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if (ret)
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return ret;
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klp_for_each_func(obj, func) {
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ret = klp_find_object_symbol(obj->name, func->old_name,
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@@ -842,6 +876,12 @@ int klp_register_patch(struct klp_patch *patch)
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{
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int ret;
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if (!is_livepatch_module(patch->mod)) {
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pr_err("module %s is not marked as a livepatch module",
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patch->mod->name);
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return -EINVAL;
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}
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if (!klp_initialized())
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return -ENODEV;
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