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=-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=unavailable 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 BF2A4C433E0 for ; Mon, 1 Mar 2021 19:36:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74E9160230 for ; Mon, 1 Mar 2021 19:36:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241964AbhCATdr (ORCPT ); Mon, 1 Mar 2021 14:33:47 -0500 Received: from mail.kernel.org ([198.145.29.99]:51736 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236189AbhCAQxz (ORCPT ); Mon, 1 Mar 2021 11:53:55 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1C8CF64F33; Mon, 1 Mar 2021 16:34:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614616458; bh=feBdjRYDWe5vGF9XXW529j2ylo7Zk7AzA1b3i1qVHXo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Uezb4e8RUgJ6t+uRZstpdKVDloofJlYM1c5T4dj31DR6tXiey7F8aQpAaw4E9KdYm 3KfEbJUAu121RQF2xR2RnHThoDpRn7JAREdM8gfXaNe3cOEb5v20YIjCzGk5bAqeNk ftkKIbzEkUbhTlVQP2Y+laVXPpv3kTcHz0fDh3c4= 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 4.14 157/176] module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for undefined symbols Date: Mon, 1 Mar 2021 17:13:50 +0100 Message-Id: <20210301161028.817651209@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161020.931630716@linuxfoundation.org> References: <20210301161020.931630716@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 @@ -2247,6 +2247,21 @@ 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) { @@ -2292,8 +2307,10 @@ 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; pr_warn("%s: Unknown symbol %s (err %li)\n",