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Mon, 9 Nov 2020 06:13:55 +0000 Subject: Re: [PATCH bpf] libbpf: don't attempt to load unused subprog as an entry-point BPF program To: Andrii Nakryiko , , , , CC: , Dmitrii Banshchikov References: <20201107000251.256821-1-andrii@kernel.org> From: Yonghong Song Message-ID: <67fdbee5-14ba-360b-269f-d7030bd7062a@fb.com> Date: Sun, 8 Nov 2020 22:13:52 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 In-Reply-To: <20201107000251.256821-1-andrii@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:788d] X-ClientProxiedBy: MWHPR19CA0008.namprd19.prod.outlook.com (2603:10b6:300:d4::18) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21cf::1046] (2620:10d:c090:400::5:788d) by MWHPR19CA0008.namprd19.prod.outlook.com (2603:10b6:300:d4::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3499.19 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: d0f2cbc7-bdcd-4c84-4c3d-08d88476a327 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Nov 2020 06:13:55.3592 (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: FUrFZN1+43+tI/++QtxJcunWwlI0kcW4AgdHdXLfWUePGDQ1dIyc9b1xWxp1dXgq X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR15MB4236 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312,18.0.737 definitions=2020-11-09_01:2020-11-05,2020-11-09 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 clxscore=1015 suspectscore=0 lowpriorityscore=0 malwarescore=0 adultscore=0 phishscore=0 bulkscore=0 mlxscore=0 priorityscore=1501 impostorscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011090039 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 11/6/20 4:02 PM, Andrii Nakryiko wrote: > If BPF code contains unused BPF subprogram and there are no other subprogram > calls (which can realistically happen in real-world applications given > sufficiently smart Clang code optimizations), libbpf will erroneously assume > that subprograms are entry-point programs and will attempt to load them with > UNSPEC program type. > > Fix by not relying on subcall instructions and rather detect it based on the > structure of BPF object's sections. > > Reported-by: Dmitrii Banshchikov > Fixes: 9a94f277c4fb ("tools: libbpf: restore the ability to load programs from .text section") > Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song