From nobody Mon Apr 6 21:11:52 2026 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 7EFC3C433FE for ; Thu, 6 Oct 2022 14:18:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231823AbiJFOSS (ORCPT ); Thu, 6 Oct 2022 10:18:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56096 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231735AbiJFORa (ORCPT ); Thu, 6 Oct 2022 10:17:30 -0400 Received: from mail-m118206.qiye.163.com (mail-m118206.qiye.163.com [115.236.118.206]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id AC8CC57241 for ; Thu, 6 Oct 2022 07:15:02 -0700 (PDT) Received: from lyc-workstation.. (unknown [221.212.176.62]) by mail-m118206.qiye.163.com (HMail) with ESMTPA id 38763BE0B01; Thu, 6 Oct 2022 22:14:58 +0800 (CST) From: YingChi Long To: me@inclyc.cn Cc: bp@alien8.de, chang.seok.bae@intel.com, dave.hansen@linux.intel.com, hpa@zytor.com, linux-kernel@vger.kernel.org, mingo@redhat.com, ndesaulniers@google.com, pbonzini@redhat.com, tglx@linutronix.de, x86@kernel.org, david.laight@aculab.com Subject: [PATCH v3] x86/fpu: use _Alignof to avoid UB in TYPE_ALIGN Date: Thu, 6 Oct 2022 22:14:42 +0800 Message-Id: <20221006141442.2475978-1-me@inclyc.cn> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220925153151.2467884-1-me@inclyc.cn> References: <20220925153151.2467884-1-me@inclyc.cn> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFPN1dZLVlBSVdZDwkaFQgSH1lBWUJOGkpWQktITU1PHhgYQxlJVQIWExYaEhckFA4PWV dZGBILWUFZSUlKVUlKSVVKTE1VTUlZV1kWGg8SFR0UWUFZT0tIVUpJS0NOTVVKS0tVS1kG X-HM-Sender-Digest: e1kMHhlZQR0aFwgeV1kSHx4VD1lBWUc6MD46Fgw6TjlOATYuM09POSxN DghPFDpVSlVKTU1OS01OTUJCSk1CVTMWGhIXVRYeOxIVGBcCGFUYFUVZV1kSC1lBWUlJSlVJSklV SkxNVU1JWVdZCAFZQUhOSU03Bg++ X-HM-Tid: 0a83ada645d02d28kusn38763be0b01 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" WG14 N2350 made very clear that it is an UB having type definitions with in "offsetof". This patch change the implementation of macro "TYPE_ALIGN" to builtin "_Alignof" to avoid undefined behavior. I've grepped all source files to find any type definitions within "offsetof". offsetof\(struct .*\{ .*, This implementation of macro "TYPE_ALIGN" seemes to be the only case of type definitions within offsetof in the kernel codebase. I've made a clang patch that rejects any definitions within __builtin_offsetof (usually #defined with "offsetof"), and tested compiling with this patch, there are no error if this patch applied. ISO C11 _Alignof is subtly different from the GNU C extension __alignof__. __alignof__ is the preferred alignment and _Alignof the minimal alignment. For 'long long' on x86 these are 8 and 4 respectively. The macro TYPE_ALIGN we're replacing has behavior that matches _Alignof rather than __alignof__. Signed-off-by: YingChi Long Link: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm Link: https://godbolt.org/z/sPs1GEhbT Link: https://gcc.gnu.org/onlinedocs/gcc/Alignment.html Link: https://reviews.llvm.org/D133574 Reviewed-by: Nick Desaulniers --- v3: - commit message changes suggested by Nick and David v2: https://lore.kernel.org/all/20220927153338.4177854-1-me@inclyc.cn/ --- arch/x86/kernel/fpu/init.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index 621f4b6cac4a..de96c11e1fe9 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -133,9 +133,6 @@ static void __init fpu__init_system_generic(void) fpu__init_system_mxcsr(); } -/* Get alignment of the TYPE. */ -#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test) - /* * Enforce that 'MEMBER' is the last field of 'TYPE'. * @@ -143,8 +140,8 @@ static void __init fpu__init_system_generic(void) * because that's how C aligns structs. */ #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \ - BUILD_BUG_ON(sizeof(TYPE) !=3D ALIGN(offsetofend(TYPE, MEMBER), \ - TYPE_ALIGN(TYPE))) + BUILD_BUG_ON(sizeof(TYPE) !=3D \ + ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE))) /* * We append the 'struct fpu' to the task_struct: -- 2.35.1