From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751753AbdJRQSm (ORCPT ); Wed, 18 Oct 2017 12:18:42 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:46383 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751287AbdJRQSk (ORCPT ); Wed, 18 Oct 2017 12:18:40 -0400 X-Google-Smtp-Source: ABhQp+SYzf23Vbbr3ItADIlWPmaJgPIctwpATThndyFu4Squ6uezZoEZop+RqV6jAP0omUU9/E3pSg== Date: Wed, 18 Oct 2017 18:18:36 +0200 From: Ingo Molnar To: Dave Hansen Cc: linux-kernel@vger.kernel.org, x86@kernel.org, luto@kernel.org, brgerst@gmail.com Subject: Re: [PATCH] x86, syscalls: use SYSCALL_DEFINE() macros for sys_modify_ldt() Message-ID: <20171018161836.ns3qxf452iii67i5@gmail.com> References: <20171017192231.72C327B4@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20171017192231.72C327B4@viggo.jf.intel.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Dave Hansen wrote: > > We do not have tracepoints for sys_modify_ldt() because we define > it directly instead of using the normal SYSCALL_DEFINEx() macros. > > However, there is a reason sys_modify_ldt() does not use the macros: > it has an 'int' return type instead of 'unsigned long'. This is > a bug, but it's a bug cemented in the ABI. > > What does this mean? If we return -EINVAL from a function that > returns 'int', we have 0x00000000ffffffea in %rax. But, if we > return -EINVAL from a function returning 'unsigned long', we end > up with 0xffffffffffffffea in %rax, which is wrong. > > To work around this and maintain the 'int' behavior while using > the SYSCALL_DEFINEx() macros, so we add a cast to 'unsigned int' > in both implementations of sys_modify_ldt(). > > Cc: x86@kernel.org > Cc: Andy Lutomirski > Cc: Brian Gerst > > --- > > b/arch/x86/include/asm/syscalls.h | 2 +- > b/arch/x86/kernel/ldt.c | 16 +++++++++++++--- > b/arch/x86/um/ldt.c | 6 ++++-- > 3 files changed, 18 insertions(+), 6 deletions(-) Fails to build on UML: /home/mingo/tip/arch/x86/um/ldt.c:372:29: error: expected ‘)’ before ‘int’ SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr , ^ /home/mingo/tip/arch/x86/um/ldt.c:206:13: warning: ‘do_modify_ldt_skas’ defined but not used [-Wunused-function] static long do_modify_ldt_skas(int func, void __user *ptr, etc. Thanks, Ingo