From patchwork Mon Mar 1 16:14:04 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 389980 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=-23.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING, 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 8E876C4646E for ; Mon, 1 Mar 2021 17:24:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C44465071 for ; Mon, 1 Mar 2021 17:24:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238276AbhCARYE (ORCPT ); Mon, 1 Mar 2021 12:24:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:37350 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237347AbhCARSx (ORCPT ); Mon, 1 Mar 2021 12:18:53 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 77F7D65052; Mon, 1 Mar 2021 16:47:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614617234; bh=7xC4iiMmZejp3ZwjMd4Sr6JX15PfpU1FJ+v4WJcqEw4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J4mI2TtVVhd/VqiBN2DlUV1VPhVsZjPyNe+BFWhnMdmcd3ZAvV6BcCgG2MQv/puLS ZjFHQ8jV+Z+K93nnNYHOT/RxBkDKAhTM9+MWQjAeGJ3Qj7Z8Cxmdg6aT8uiK22dSdU BVZbyJ1mbnBnrlUiphc0ca6sgrWrdexalUExRR/4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Marco Elver , Nick Desaulniers , Nathan Chancellor , Fangrui Song , Jessica Yu Subject: [PATCH 4.19 224/247] module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for undefined symbols Date: Mon, 1 Mar 2021 17:14:04 +0100 Message-Id: <20210301161042.653694736@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161031.684018251@linuxfoundation.org> References: <20210301161031.684018251@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Fangrui Song commit ebfac7b778fac8b0e8e92ec91d0b055f046b4604 upstream. clang-12 -fno-pic (since https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6) can emit `call __stack_chk_fail@PLT` instead of `call __stack_chk_fail` on x86. The two forms should have identical behaviors on x86-64 but the former causes GNU as<2.37 to produce an unreferenced undefined symbol _GLOBAL_OFFSET_TABLE_. (On x86-32, there is an R_386_PC32 vs R_386_PLT32 difference but the linker behavior is identical as far as Linux kernel is concerned.) Simply ignore _GLOBAL_OFFSET_TABLE_ for now, like what scripts/mod/modpost.c:ignore_undef_symbol does. This also fixes the problem for gcc/clang -fpie and -fpic, which may emit `call foo@PLT` for external function calls on x86. Note: ld -z defs and dynamic loaders do not error for unreferenced undefined symbols so the module loader is reading too much. If we ever need to ignore more symbols, the code should be refactored to ignore unreferenced symbols. Cc: Link: https://github.com/ClangBuiltLinux/linux/issues/1250 Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27178 Reported-by: Marco Elver Reviewed-by: Nick Desaulniers Reviewed-by: Nathan Chancellor Tested-by: Marco Elver Signed-off-by: Fangrui Song Signed-off-by: Jessica Yu Signed-off-by: Greg Kroah-Hartman --- kernel/module.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) --- a/kernel/module.c +++ b/kernel/module.c @@ -2274,6 +2274,21 @@ static int verify_export_symbols(struct return 0; } +static bool ignore_undef_symbol(Elf_Half emachine, const char *name) +{ + /* + * On x86, PIC code and Clang non-PIC code may have call foo@PLT. GNU as + * before 2.37 produces an unreferenced _GLOBAL_OFFSET_TABLE_ on x86-64. + * i386 has a similar problem but may not deserve a fix. + * + * If we ever have to ignore many symbols, consider refactoring the code to + * only warn if referenced by a relocation. + */ + if (emachine == EM_386 || emachine == EM_X86_64) + return !strcmp(name, "_GLOBAL_OFFSET_TABLE_"); + return false; +} + /* Change all symbols so that st_value encodes the pointer directly. */ static int simplify_symbols(struct module *mod, const struct load_info *info) { @@ -2319,8 +2334,10 @@ static int simplify_symbols(struct modul break; } - /* Ok if weak. */ - if (!ksym && ELF_ST_BIND(sym[i].st_info) == STB_WEAK) + /* Ok if weak or ignored. */ + if (!ksym && + (ELF_ST_BIND(sym[i].st_info) == STB_WEAK || + ignore_undef_symbol(info->hdr->e_machine, name))) break; ret = PTR_ERR(ksym) ?: -ENOENT;