From patchwork Sat Jun 10 09:13:10 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Masahiro Yamada X-Patchwork-Id: 105910 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:994d:0:b0:3d9:f83d:47d9 with SMTP id k13csp1435860vqr; Sat, 10 Jun 2023 02:14:57 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ7T5lEw46Se6LHd2jAVh9OBNsM72d+dmddYrCb7OPDiUhKDa0EIUKFlAxqOgVehcXqI149D X-Received: by 2002:a05:6a00:228a:b0:648:c1be:496 with SMTP id f10-20020a056a00228a00b00648c1be0496mr5570794pfe.22.1686388497433; Sat, 10 Jun 2023 02:14:57 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1686388497; cv=none; d=google.com; s=arc-20160816; b=qlUPvVRLSXnU2ySRiwIp8nJEpVT/hc5lUjk23OtP00fH+galQpeQDc/XURbD52BT7d t9xeNhpmj8dxV6Mgdd5rMNaglLpoMS9HR64C8uExmwZSAUM244dMBQXCc4zeRPFuA7Tl NQ5wOQdSX8f6dOKshM1iylGnNa45dUUjP+1+1vYOdwdcjIPk3iKcXD5ht/0WisCfp6uL IuDB6Xzb0ixwVKqhGGR+KWizlbe4zXxpCCRg/z/HCgfMqiyP9Lcqz1MOw02tDdOrotAa 7GWrHV7AaOJpY9Pa7slcPXLqegNCcm3q2jm3gTAfviKzAHzfoPobsydciGgEw1YzXeQS YlBg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=AdbQxjbWmwTPXQIqnOBe8rpn2g3+FG/L0GCGseIl6I4=; b=MmipkloraF19Gg9fg54hTTZPUmvoZgkMdjHYJTfnCn8zhEPEUCsEymrJ8/St9qaI0c VCvVtdv3/8o421BcYHrouZ109Xb4rH1UTIf0GUx532bz/sQgFKXsPn2ttEqu22xCOtQf ei1Swv2cC8nnbaKH0xY7p2GBAM2YRnjsBQQF85k3cxz1X7hpA5AstxThhk1LlaqTHQ8+ PP2Mb8vKr6ahIHcGASTX00r8z4gdvxJfhmItAPmMm3LBT0h9oWhT9ii8GpA8lU3p3oWC Rayq+UC8vwT49CbkwQ39WXBAc8sRcl9yw17x4UsntvLwLzuQ7px9GOTvp5jhBzV6LcSF gx/g== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=S6Prepz6; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id b3-20020aa78ec3000000b00653d48605fbsi3694553pfr.358.2023.06.10.02.14.44; Sat, 10 Jun 2023 02:14:57 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=S6Prepz6; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234183AbjFJJNg (ORCPT + 99 others); Sat, 10 Jun 2023 05:13:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233969AbjFJJNe (ORCPT ); Sat, 10 Jun 2023 05:13:34 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95A5B3A98; Sat, 10 Jun 2023 02:13:33 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 329C36153F; Sat, 10 Jun 2023 09:13:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2618EC4339E; Sat, 10 Jun 2023 09:13:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686388412; bh=PG6qM3vqxiF+KiiI8e2eBOByJ2994aew6fGGaTXEDyQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=S6Prepz6fIDlWpYHwo+9GvbzqBuM0yICauO1hNBqTYUTFjVwRJ2A0lsojWnWQfAW9 E+H/EcPwloHdGH8EOaFUCpZZaKRYY/nC3wUDs2wo9W8ZC7EJKYS0F7zHR/ofrmlh/v 7fRcIPItpQmvYMQK/mgnO3kGpfNEMZjqCNkhTJ3wf6ElyFdIRm9M7pDSJs0759DCuD G/WqKt24BtW4yNHYCFqDK5+RF7OMiSET7bdQXWtk0JtPjE7/fsD2+kH3G9V1tkragf Nb6cmBtVQvYyCeoJXlKlnvj3e5BbZJ2JyfDObDdF5aEQX2ccufJamt9+gRcPCHVze6 CfmWqoWkESXqg== From: Masahiro Yamada To: linux-kbuild@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Nathan Chancellor , Nick Desaulniers , Nicolas Schier , linux-um@lists.infradead.org, Masahiro Yamada Subject: [PATCH v8 01/11] Revert "[PATCH] uml: export symbols added by GCC hardened" Date: Sat, 10 Jun 2023 18:13:10 +0900 Message-Id: <20230610091320.1054554-2-masahiroy@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230610091320.1054554-1-masahiroy@kernel.org> References: <20230610091320.1054554-1-masahiroy@kernel.org> MIME-Version: 1.0 X-Spam-Status: No, score=-7.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1768306505590022841?= X-GMAIL-MSGID: =?utf-8?q?1768306505590022841?= This reverts commit cead61a6717a9873426b08d73a34a325e3546f5d. It exported __stack_smash_handler and __guard, while they may not be defined by anyone. The code *declares* __stack_smash_handler and __guard. It does not create weak symbols. If no external library is linked, they are left undefined, but yet exported. If a loadable module tries to access non-existing symbols, bad things (a page fault, NULL pointer dereference, etc.) will happen. So, the current code is wrong and dangerous. If the code were written as follows, it would *define* them as weak symbols so modules would be able to get access to them. void (*__stack_smash_handler)(void *) __attribute__((weak)); EXPORT_SYMBOL(__stack_smash_handler); long __guard __attribute__((weak)); EXPORT_SYMBOL(__guard); In fact, modpost forbids exporting undefined symbols. It shows an error message if it detects such a mistake. ERROR: modpost: "..." [...] was exported without definition Unfortunately, it is checked only when the code is built as modular. The problem described above has been unnoticed for a long time because arch/um/os-Linux/user_syms.c is always built-in. With a planned change in Kbuild, exporting undefined symbols will always result in a build error instead of a run-time error. It is a good thing, but we need to fix the breakage in advance. One fix is to define weak symbols as shown above. An alternative is to export them conditionally as follows: #ifdef CONFIG_STACKPROTECTOR extern void __stack_smash_handler(void *); EXPORT_SYMBOL(__stack_smash_handler); external long __guard; EXPORT_SYMBOL(__guard); #endif This is what other architectures do; EXPORT_SYMBOL(__stack_chk_guard) is guarded by #ifdef CONFIG_STACKPROTECTOR. However, adding the #ifdef guard is not sensible because UML cannot enable the stack-protector in the first place! (Please note UML does not select HAVE_STACKPROTECTOR in Kconfig.) So, the code is already broken (and unused) in multiple ways. Just remove. Signed-off-by: Masahiro Yamada Reviewed-by: Nick Desaulniers --- (no changes since v7) Changes in v7: - New patch arch/um/os-Linux/user_syms.c | 7 ------- 1 file changed, 7 deletions(-) diff --git a/arch/um/os-Linux/user_syms.c b/arch/um/os-Linux/user_syms.c index 9b62a9d352b3..a310ae27b479 100644 --- a/arch/um/os-Linux/user_syms.c +++ b/arch/um/os-Linux/user_syms.c @@ -37,13 +37,6 @@ EXPORT_SYMBOL(vsyscall_ehdr); EXPORT_SYMBOL(vsyscall_end); #endif -/* Export symbols used by GCC for the stack protector. */ -extern void __stack_smash_handler(void *) __attribute__((weak)); -EXPORT_SYMBOL(__stack_smash_handler); - -extern long __guard __attribute__((weak)); -EXPORT_SYMBOL(__guard); - #ifdef _FORTIFY_SOURCE extern int __sprintf_chk(char *str, int flag, size_t len, const char *format); EXPORT_SYMBOL(__sprintf_chk);