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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 6521FC43219 for ; Fri, 3 May 2019 11:31:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B1C12075C for ; Fri, 3 May 2019 11:31:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727635AbfECLbp convert rfc822-to-8bit (ORCPT ); Fri, 3 May 2019 07:31:45 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:23808 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726372AbfECLbp (ORCPT ); Fri, 3 May 2019 07:31:45 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-119-bsrUedipMsKCwape80AdzQ-1; Fri, 03 May 2019 12:31:41 +0100 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; Fri, 3 May 2019 12:31:40 +0100 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; Fri, 3 May 2019 12:31:40 +0100 From: David Laight To: 'Cyrill Gorcunov' , Joel Savitz CC: "linux-kernel@vger.kernel.org" , "Thomas Gleixner" , Ingo Molnar , "Masami Hiramatsu" , Waiman Long , "Mauro Carvalho Chehab" , Kristina Martsenko , Andrew Morton , Kees Cook , "Gustavo A. R. Silva" , YueHaibing , Micah Morton , Yang Shi , Jann Horn , Alexey Dobriyan , Rafael Aquini , Michael Kerrisk , Yury Norov Subject: RE: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK_SIZE option to prctl(2) Thread-Topic: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK_SIZE option to prctl(2) Thread-Index: AQHVAYqqcxRhj7bMTkeIUrrm9JebiKZZRD3w Date: Fri, 3 May 2019 11:31:40 +0000 Message-ID: <6cf43408000149d98cc1683943c436cb@AcuMS.aculab.com> References: <1556830342-32307-1-git-send-email-jsavitz@redhat.com> <1556830342-32307-2-git-send-email-jsavitz@redhat.com> <20190502210922.GF2488@uranus.lan> <20190503083149.GH2488@uranus.lan> In-Reply-To: <20190503083149.GH2488@uranus.lan> Accept-Language: en-GB, en-US Content-Language: 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 X-MC-Unique: bsrUedipMsKCwape80AdzQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Cyrill Gorcunov > Sent: 03 May 2019 09:32 > On Thu, May 02, 2019 at 05:46:08PM -0400, Joel Savitz wrote: > > > Won't be possible to use put_user here? Something like > > > > > > static int prctl_get_tasksize(unsigned long __user *uaddr) > > > { > > > return put_user(TASK_SIZE, uaddr) ? -EFAULT : 0; > > > } > > > > What would be the benefit of using put_user() over copy_to_user() in > > this context? > > It is a common pattern to use put_user with native types, where > copy_to_user more biased for composed types transfer. It also removes all the crappy code that checks whether the kernel buffer is valid. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)