From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03FF3C3A5AA for ; Thu, 5 Sep 2019 12:46:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF1A122476 for ; Thu, 5 Sep 2019 12:46:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389488AbfIEMpU (ORCPT ); Thu, 5 Sep 2019 08:45:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:40662 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731438AbfIEMpS (ORCPT ); Thu, 5 Sep 2019 08:45:18 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id D3497B656; Thu, 5 Sep 2019 12:45:16 +0000 (UTC) From: Miroslav Benes To: jikos@kernel.org, jpoimboe@redhat.com, pmladek@suse.com Cc: joe.lawrence@redhat.com, nstange@suse.de, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, Miroslav Benes Subject: [RFC PATCH v2 1/3] livepatch: Clear relocation targets on a module removal Date: Thu, 5 Sep 2019 14:45:12 +0200 Message-Id: <20190905124514.8944-2-mbenes@suse.cz> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190905124514.8944-1-mbenes@suse.cz> References: <20190905124514.8944-1-mbenes@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Josh reported a bug: When the object to be patched is a module, and that module is rmmod'ed and reloaded, it fails to load with: module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' The livepatch module has a relocation which references a symbol in the _previous_ loading of nfsd. When apply_relocate_add() tries to replace the old relocation with a new one, it sees that the previous one is nonzero and it errors out. On ppc64le, we have a similar issue: module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd] livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' He also proposed three different solutions. We could remove the error check in apply_relocate_add() introduced by commit eda9cec4c9a1 ("x86/module: Detect and skip invalid relocations"). However the check is useful for detecting corrupted modules. We could also deny the patched modules to be removed. If it proved to be a major drawback for users, we could still implement a different approach. The solution would also complicate the existing code a lot. We thus decided to reverse the relocation patching (clear all relocation targets on x86_64, or return back nops on powerpc). The solution is not universal and is too much arch-specific, but it may prove to be simpler in the end. Reported-by: Josh Poimboeuf Signed-off-by: Miroslav Benes --- arch/powerpc/kernel/module_64.c | 45 +++++++++++++++++++++++++++++++++ arch/s390/kernel/module.c | 8 ++++++ arch/x86/kernel/module.c | 43 +++++++++++++++++++++++++++++++ include/linux/moduleloader.h | 7 +++++ kernel/livepatch/core.c | 45 +++++++++++++++++++++++++++++++++ 5 files changed, 148 insertions(+) diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index a93b10c48000..e461d456e447 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c @@ -741,6 +741,51 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, return 0; } +#ifdef CONFIG_LIVEPATCH +void clear_relocate_add(Elf64_Shdr *sechdrs, + const char *strtab, + unsigned int symindex, + unsigned int relsec, + struct module *me) +{ + unsigned int i; + Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr; + Elf64_Sym *sym; + unsigned long *location; + const char *symname; + u32 *instruction; + + pr_debug("Applying ADD relocate section %u to %u\n", relsec, + sechdrs[relsec].sh_info); + + for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) { + location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr + + rela[i].r_offset; + sym = (Elf64_Sym *)sechdrs[symindex].sh_addr + + ELF64_R_SYM(rela[i].r_info); + symname = me->core_kallsyms.strtab + + sym->st_name; + + if (ELF64_R_TYPE(rela[i].r_info) != R_PPC_REL24) + continue; + + if (sym->st_shndx != SHN_UNDEF && + sym->st_shndx != SHN_LIVEPATCH) + continue; + + instruction = (u32 *)location; + if (is_mprofile_mcount_callsite(symname, instruction)) + continue; + + if (!instr_is_relative_link_branch(*instruction)) + continue; + + instruction += 1; + *instruction = PPC_INST_NOP; + } +} +#endif + #ifdef CONFIG_DYNAMIC_FTRACE #ifdef CONFIG_MPROFILE_KERNEL diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c index 31889db609e9..56867d052010 100644 --- a/arch/s390/kernel/module.c +++ b/arch/s390/kernel/module.c @@ -437,6 +437,14 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab, return 0; } +#ifdef CONFIG_LIVEPATCH +void clear_relocate_add(Elf64_Shdr *sechdrs, const char *strtab, + unsigned int symindex, unsigned int relsec, + struct module *me) +{ +} +#endif + int module_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, struct module *me) diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index d5c72cb877b3..b07d71f125e6 100644 --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -215,6 +215,49 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, me->name); return -ENOEXEC; } + +#ifdef CONFIG_LIVEPATCH +void clear_relocate_add(Elf64_Shdr *sechdrs, + const char *strtab, + unsigned int symindex, + unsigned int relsec, + struct module *me) +{ + unsigned int i; + Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr; + void *loc; + + DEBUGP("Clearing relocate section %u to %u\n", + relsec, sechdrs[relsec].sh_info); + for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) { + loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr + + rel[i].r_offset; + + switch (ELF64_R_TYPE(rel[i].r_info)) { + case R_X86_64_NONE: + break; + case R_X86_64_64: + *(u64 *)loc = 0; + break; + case R_X86_64_32: + *(u32 *)loc = 0; + break; + case R_X86_64_32S: + *(s32 *)loc = 0; + break; + case R_X86_64_PC32: + case R_X86_64_PLT32: + *(u32 *)loc = 0; + break; + case R_X86_64_PC64: + *(u64 *)loc = 0; + break; + default: + break; + } + } +} +#endif #endif int module_finalize(const Elf_Ehdr *hdr, diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h index 31013c2effd3..f1e52692db5f 100644 --- a/include/linux/moduleloader.h +++ b/include/linux/moduleloader.h @@ -62,6 +62,13 @@ int apply_relocate_add(Elf_Shdr *sechdrs, unsigned int symindex, unsigned int relsec, struct module *mod); +#ifdef CONFIG_LIVEPATCH +void clear_relocate_add(Elf64_Shdr *sechdrs, + const char *strtab, + unsigned int symindex, + unsigned int relsec, + struct module *me); +#endif #else static inline int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab, diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index ab4a4606d19b..f0b380d2a17a 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -295,6 +295,45 @@ static int klp_write_object_relocations(struct module *pmod, return ret; } +static void klp_clear_object_relocations(struct module *pmod, + struct klp_object *obj) +{ + int i, cnt; + const char *objname, *secname; + char sec_objname[MODULE_NAME_LEN]; + Elf_Shdr *sec; + + objname = klp_is_module(obj) ? obj->name : "vmlinux"; + + /* For each klp relocation section */ + for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) { + sec = pmod->klp_info->sechdrs + i; + secname = pmod->klp_info->secstrings + sec->sh_name; + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH)) + continue; + + /* + * Format: .klp.rela.sec_objname.section_name + * See comment in klp_resolve_symbols() for an explanation + * of the selected field width value. + */ + secname = pmod->klp_info->secstrings + sec->sh_name; + cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname); + if (cnt != 1) { + pr_err("section %s has an incorrectly formatted name\n", + secname); + continue; + } + + if (strcmp(objname, sec_objname)) + continue; + + clear_relocate_add(pmod->klp_info->sechdrs, + pmod->core_kallsyms.strtab, + pmod->klp_info->symndx, i, pmod); + } +} + /* * Sysfs Interface * @@ -1100,6 +1139,12 @@ static void klp_cleanup_module_patches_limited(struct module *mod, klp_post_unpatch_callback(obj); + mutex_lock(&text_mutex); + module_disable_ro(patch->mod); + klp_clear_object_relocations(patch->mod, obj); + module_enable_ro(patch->mod, true); + mutex_unlock(&text_mutex); + klp_free_object_loaded(obj); break; } -- 2.23.0