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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7EA0C433E0 for ; Mon, 4 Jan 2021 12:18:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7009C20757 for ; Mon, 4 Jan 2021 12:18:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726579AbhADMSf convert rfc822-to-8bit (ORCPT ); Mon, 4 Jan 2021 07:18:35 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:23205 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726236AbhADMSf (ORCPT ); Mon, 4 Jan 2021 07:18:35 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-161-e-HVRhClO9mndLuADFhIAA-1; Mon, 04 Jan 2021 12:16:56 +0000 X-MC-Unique: e-HVRhClO9mndLuADFhIAA-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 4 Jan 2021 12:16:56 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 4 Jan 2021 12:16:56 +0000 From: David Laight To: Al Viro , Christoph Hellwig , "linux-kernel@vger.kernel.org" Subject: in_compat_syscall() on x86 Thread-Topic: in_compat_syscall() on x86 Thread-Index: Adbikf8I52+Fp/HYSH2MXxqk00t/Og== Date: Mon, 4 Jan 2021 12:16:56 +0000 Message-ID: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On x86 in_compat_syscall() is defined as: in_ia32_syscall() || in_x32_syscall() Now in_ia32_syscall() is a simple check of the TS_COMPAT flag. However in_x32_syscall() is a horrid beast that has to indirect through to the original %eax value (ie the syscall number) and check for a bit there. So on a kernel with x32 support (probably most distro kernels) the in_compat_syscall() check is rather more expensive than one might expect. It would be muck better if both checks could be done together. I think this would require the syscall entry code to set a value in both the 64bit and x32 entry paths. (Can a process make both 64bit and x32 system calls?) To do this sensible (probably) requires a byte be allocated to hold the syscall type - rather than using flag bits in the 'status' field. Apart from the syscall entry, the exec code seems to change the syscall type to that of the binary being executed. I didn't spot anything else that changes the fields. But I failed to find the full list of allocated bits for the 'status' field. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)