Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755659AbdLGN16 (ORCPT ); Thu, 7 Dec 2017 08:27:58 -0500 Received: from mail-eopbgr00104.outbound.protection.outlook.com ([40.107.0.104]:52512 "EHLO EUR02-AM5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754926AbdLGN1y (ORCPT ); Thu, 7 Dec 2017 08:27:54 -0500 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=aryabinin@virtuozzo.com; Subject: Re: [PATCH v2] ubsan: don't handle misaligned address when support unaligned access To: Andrew Morton , Ding Tianhong Cc: "linux-kernel@vger.kernel.org" , LinuxArm , David Laight References: <5b905d56-609e-3822-096a-3b93b3eb7675@huawei.com> <20171206164916.687d5006b7a49ef1149e7154@linux-foundation.org> From: Andrey Ryabinin Message-ID: <022fdf6b-6e00-fe70-3124-80b8ff50a859@virtuozzo.com> Date: Thu, 7 Dec 2017 16:31:23 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 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X-Microsoft-Exchange-Diagnostics: 1;DB6PR08MB2824;20:Pmqu2Z9NXRqUHYGcBNBeGXzYMNyRj2RmoxaPRVbefdXOScSjVP9x4NqxwB9QoWcaLFU1gBYTs1oo+x6z9xunDUGgAEELCK2lZCPB57tXM7fHJ274fbciBCzoIFn8rtaNoUdJbETMNRE8qoIlKS4t0qyZe9QvXJlpSHXIevD6o9A= X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Dec 2017 13:27:52.0887 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d21fe85b-6fd7-4fb5-be5f-08d53d765190 X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB6PR08MB2824 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1343 Lines: 32 On 12/07/2017 03:49 AM, Andrew Morton wrote: > (correcting Andrey's email address) > > > From: Ding Tianhong > Subject: lib/ubsan.c: don't handle misaligned address when kernel supports unaligned access > > ubsan reports a warning like: > > UBSAN: Undefined behaviour in ../include/linux/etherdevice.h:386:9 > load of misaligned address ffffffc069ba0482 for type 'long unsigned int' > which requires 8 byte alignment > CPU: 0 PID: 901 Comm: sshd Not tainted 4.xx+ #1 > Hardware name: linux,dummy-virt (DT) > Call trace: > [] dump_backtrace+0x0/0x348 > [] show_stack+0x20/0x30 > [] dump_stack+0x144/0x1b4 > [] ubsan_epilogue+0x18/0x74 > [] __ubsan_handle_type_mismatch+0x1a0/0x25c > [] dev_gro_receive+0x17d8/0x1830 > [] napi_gro_receive+0x30/0x158 > [] virtnet_receive+0xad4/0x1fa8 > > The reason is that when enabling the CONFIG_UBSAN_ALIGNMENT, ubsan will > report the unaligned access even if the system supports it > (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). This produces a lot of noise > in the log and causes confusion. > NACK. This doesn't make sense. If you don't want to see misaligned access reports you simply shouldn't enable CONFIG_UBSAN_ALIGNMENT.