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Tue, 19 May 2020 01:00:11 +0000 From: Yonghong Song Subject: Re: UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177 To: Andrii Nakryiko , Qian Cai CC: Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Andrii Nakryiko , John Fastabend , KP Singh , Linux Netdev List , bpf , Linux Kernel Mailing List , clang-built-linux , Kees Cook References: Message-ID: <45f9ef5d-18e3-c92f-e7a9-1c6d6405e478@fb.com> Date: Mon, 18 May 2020 18:00:01 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR04CA0027.namprd04.prod.outlook.com (2603:10b6:a03:1d0::37) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from stephyma-mbp.dhcp.thefacebook.com (2620:10d:c090:400::5:f205) by BY5PR04CA0027.namprd04.prod.outlook.com (2603:10b6:a03:1d0::37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.25 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 8b9e7b90-6731-4acc-146b-08d7fb8ffb2f X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 May 2020 01:00:11.3014 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: SDHabtcaoouTk0cFSHhZfHwG2/cutGnzw0xNPKSa1CZ1pQ6FSQNd7piWZQ2SAxgq X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2550 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.676 definitions=2020-05-18_06:2020-05-15,2020-05-18 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=27 bulkscore=0 impostorscore=0 spamscore=0 phishscore=0 malwarescore=0 mlxlogscore=999 priorityscore=1501 adultscore=0 clxscore=1011 cotscore=-2147483648 mlxscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005190007 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/18/20 5:25 PM, Andrii Nakryiko wrote: > On Mon, May 18, 2020 at 5:09 PM Qian Cai wrote: >> >> On Mon, May 18, 2020 at 7:55 PM Andrii Nakryiko >> wrote: >>> >>> On Sun, May 17, 2020 at 7:45 PM Qian Cai wrote: >>>> >>>> With Clang 9.0.1, >>>> >>>> return array->value + array->elem_size * (index & array->index_mask); >>>> >>>> but array->value is, >>>> >>>> char value[0] __aligned(8); >>> >>> This, and ptrs and pptrs, should be flexible arrays. But they are in a >>> union, and unions don't support flexible arrays. Putting each of them >>> into anonymous struct field also doesn't work: >>> >>> /data/users/andriin/linux/include/linux/bpf.h:820:18: error: flexible >>> array member in a struct with no named members >>> struct { void *ptrs[] __aligned(8); }; >>> >>> So it probably has to stay this way. Is there a way to silence UBSAN >>> for this particular case? >> >> I am not aware of any way to disable a particular function in UBSAN >> except for the whole file in kernel/bpf/Makefile, >> >> UBSAN_SANITIZE_arraymap.o := n >> >> If there is no better way to do it, I'll send a patch for it. > > > That's probably going to be too drastic, we still would want to > validate the rest of arraymap.c code, probably. Not sure, maybe > someone else has better ideas. Maybe something like below? struct bpf_array { struct bpf_map map; u32 elem_size; u32 index_mask; struct bpf_array_aux *aux; union { char value; void *ptrs; void __percpu *pptrs; } u[] __aligned(8); };