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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DB547C7EE45 for ; Sat, 10 Jun 2023 09:13:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=rpN+pA9EpzuSis015ulAXxbEzPTaeHOoJxPP/xW95wA=; b=anqNu1sPHUfKoz AG3XzFkJgdjlxn4ohiwGUM/nt5tvTUbMOu95dvnExRZWnZb9XOjuOuWtD8SDpUx/pucmjl5763j29 24temGLX59SNwUtrmjeqKf2+6v+iqd6dJQzLsj8FKOU9dPQqp+Zwq0kltfHP3bkyyhGXovi5tjRoR PZOJW2S9OUlXDL1d+U/he/n3desPIXb2lB/WKkaTG4j8IZYUd5SWKiOXHIp8SuFbmtKo9N78UVHUt YbTwbf83CMYkhjA9mYl9/IoxS9JoGoDPWIl1YFauGN9dbLvHzWWlZ5ucGJyiTkKXYONomjxN44hNB x182SWAx9Ce07OPplypQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1q7ufA-00Fcak-1I; Sat, 10 Jun 2023 09:13:36 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1q7uf7-00FcZS-2v for linux-um@lists.infradead.org; Sat, 10 Jun 2023 09:13:35 +0000 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 3308B61EFC; 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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230610_021334_019892_542652A5 X-CRM114-Status: GOOD ( 14.50 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.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); -- 2.39.2 _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um