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=-0.8 required=3.0 tests=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 929B0C43603 for ; Wed, 4 Dec 2019 11:14:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C10A207DD for ; Wed, 4 Dec 2019 11:14:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727469AbfLDLOO convert rfc822-to-8bit (ORCPT ); Wed, 4 Dec 2019 06:14:14 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:51524 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727466AbfLDLON (ORCPT ); Wed, 4 Dec 2019 06:14:13 -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-171-xQ-iqH-0NqakegqgDHauPg-1; Wed, 04 Dec 2019 11:14:09 +0000 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; Wed, 4 Dec 2019 11:14:08 +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; Wed, 4 Dec 2019 11:14:08 +0000 From: David Laight To: 'Paul Burton' , "linux-mips@vger.kernel.org" CC: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Subject: RE: [PATCH] MIPS: Use __copy_{to,from}_user() for emulated FP loads/stores Thread-Topic: [PATCH] MIPS: Use __copy_{to,from}_user() for emulated FP loads/stores Thread-Index: AQHVqhshCXVq7CTTBEufX7LGTbPWHKep0u6g Date: Wed, 4 Dec 2019 11:14:08 +0000 Message-ID: References: <20191203204933.1642259-1-paulburton@kernel.org> In-Reply-To: <20191203204933.1642259-1-paulburton@kernel.org> 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: xQ-iqH-0NqakegqgDHauPg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org From: Paul Burton > Sent: 03 December 2019 20:50 > Our FPU emulator currently uses __get_user() & __put_user() to perform > emulated loads & stores. This is problematic because __get_user() & > __put_user() are only suitable for naturally aligned memory accesses, > and the address we're accessing is entirely under the control of > userland. > > This allows userland to cause a kernel panic by simply performing an > unaligned floating point load or store - the kernel will handle the > address error exception by attempting to emulate the instruction, and in > the process it may generate another address error exception itself. > This time the exception is taken with EPC pointing at the kernels FPU > emulation code, and we hit a die_if_kernel() in > emulate_load_store_insn(). Won't this be true of almost all code that uses get_user() and put_user() (with or without the leading __). > Fix this up by using __copy_from_user() instead of __get_user() and > __copy_to_user() instead of __put_user(). These replacements will handle > arbitrary alignment without problems. They'll also kill performance..... David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)