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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 704B5C001E0 for ; Mon, 24 Jul 2023 01:36:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231217AbjGXBgB (ORCPT ); Sun, 23 Jul 2023 21:36:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231714AbjGXBfq (ORCPT ); Sun, 23 Jul 2023 21:35:46 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3993846B8; Sun, 23 Jul 2023 18:32:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1749060F89; Mon, 24 Jul 2023 01:31:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 937C3C433C7; Mon, 24 Jul 2023 01:31:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690162276; bh=uRwNvojF+8pntjY3oRrKniCR3fW7tAuezWVyIEeoVLM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=En/LU/8DtUUJt9ze9IowBhzbMl+aAKuKA0hXGQhxs6ZRcwDhwkmfHjakmCq2+mNKT YSg98FRIexqbMn3fGbcvqJhpasAXrbjR5jEGMmWPgsJKyJBv5XkYFzYwoD/ZBvdRsC 1tbBp/IcUvveuLhC36OEuCaMnGpkWdSGnRCgRDosjXwhXOMNy2ieIZF1S+ozB3y6QU kmkz0qvyWt0EXOBr7yecbdcp9NqDCDhDcGOjF9bflrcvVQara/vKQGLzI4es/r89TH uXpmNMkJcuX55rMKCLu+x5TVWtoVhCasWbeTa7g7BYTFqwuPEzb5pMAxHIRDLXKpJd 7fMFH2gOBBMng== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Masahiro Yamada , Nick Desaulniers , Sasha Levin , jdike@addtoit.com, richard@nod.at, user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net Subject: [PATCH AUTOSEL 6.4 2/4] Revert "[PATCH] uml: export symbols added by GCC hardened" Date: Sun, 23 Jul 2023 21:31:09 -0400 Message-Id: <20230724013111.2327251-2-sashal@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230724013111.2327251-1-sashal@kernel.org> References: <20230724013111.2327251-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.4.5 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Masahiro Yamada [ Upstream commit 8635e8df477bc77837886da206f4915576f88fec ] 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 Signed-off-by: Sasha Levin --- 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 9b62a9d352b3a..a310ae27b479a 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