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: 13274791 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1AB81C77B7A for ; Sat, 10 Jun 2023 09:13:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234156AbjFJJNf (ORCPT ); Sat, 10 Jun 2023 05:13:35 -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 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org 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);