From patchwork Thu Jun 8 14:24:18 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Masahiro Yamada X-Patchwork-Id: 13272422 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 ABE1EC7EE23 for ; Thu, 8 Jun 2023 14:24:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237040AbjFHOY6 (ORCPT ); Thu, 8 Jun 2023 10:24:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55752 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237113AbjFHOYx (ORCPT ); Thu, 8 Jun 2023 10:24:53 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69ABE30C3; Thu, 8 Jun 2023 07:24:39 -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 D62B264E20; Thu, 8 Jun 2023 14:24:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0A036C433A0; Thu, 8 Jun 2023 14:24:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686234278; bh=7ZPyZ9apG1M05E0n0MB6gFR/gnPXwymtgzxIDVjhPog=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lyb/aRQonk8gbaoHdI0/Cb4ItgDLwxIK+DRpbx0KcKc6rNJ6Rpj7K2KQKpzmumDnE WdoNs13V76MCdMdX41tTHvhd5gocZxNMJEERi+nfhLvD9G4pTxmLMApimqHyX0L624 t4x+22sxF1nQMKsXUZNPeEion4PCNsIBz8S6PkOgZJ9Qxtcjj2th9w1H4u/onrZWcR YwxVkKN4TQA7V4Fl4JLvBPwXVE6EZ6t49WjXaMMKaPucewyNKER1YTMUKrXUqI2n5k VGJi/w9oqzpuvrSUmQueff5KNiMOeypROw8NYKdqqIjd158V/EnZqu6id2PKTe1LUF 4J3jIFYyTWWcg== 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 v7 01/11] Revert "[PATCH] uml: export symbols added by GCC hardened" Date: Thu, 8 Jun 2023 23:24:18 +0900 Message-Id: <20230608142428.256985-2-masahiroy@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230608142428.256985-1-masahiroy@kernel.org> References: <20230608142428.256985-1-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. When the stack-protector is disabled, 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. 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 --- 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);