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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 B00E1C433E6 for ; Tue, 5 Jan 2021 05:48:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 84CC322838 for ; Tue, 5 Jan 2021 05:48:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725971AbhAEFsi (ORCPT ); Tue, 5 Jan 2021 00:48:38 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:30364 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725766AbhAEFsh (ORCPT ); Tue, 5 Jan 2021 00:48:37 -0500 Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 1055ev6v015555; Mon, 4 Jan 2021 21:47:42 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : references : in-reply-to : content-type : content-id : content-transfer-encoding : mime-version; s=facebook; bh=yLk0GexK0V0FQxZdUTnIFAmr0rIG5UcSsYqOwP0pgGw=; b=Qm1q4KPVDV2ruw7BNiTazsQxqiiOa4nu8Xws2dT3r9PLRQBs6bzYhwFaYeKOUDWYXKan QBJ4SAn0OEDSxxrU5WN4k46vERGssERWTOrPCMXhEU5VQ7JFmsCHwCc+hkgKQwMIThSP SctyaHYVs8QDbxN9DCHvirjthAtfvRUmiSo= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 35u9cp7mgq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT); Mon, 04 Jan 2021 21:47:42 -0800 Received: from NAM12-DM6-obe.outbound.protection.outlook.com (100.104.31.183) by o365-in.thefacebook.com (100.104.35.175) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Mon, 4 Jan 2021 21:47:40 -0800 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=Akz/TnHyWCmyS6IdukpTpvdS9Q45fjSDQ2Rc1sXZZHFIp2Yl2DizfmgF13kmlArQaz1Z0b1e6G2oE0aNdiorVn3fI3YPDoSJgBSKuQFUyHsPHKndLnZ+RDHZydfAz1ZaS0WPuXEnIfYy4facniGbXLqdRycIq0MAC2JQP98NAf69EFS1dCeGzRlKVY5JKYIdEtzoSk5lvzrAH1SWufs1bb+zVQkOXq7OnGL3FHAvmXLtObh0weocLqgjwvvltNmovVLOkwors0rwLbk4mkazojoS5QB/9yPHi1CXOJkmsRZHZknSMQkrBpZWgrC5hOfqkyql5wsg0FqPMjmqTkZhWQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=yLk0GexK0V0FQxZdUTnIFAmr0rIG5UcSsYqOwP0pgGw=; b=kSlm41epeS++XYNgWkivTurDsXr0UD246h0M+1swdinjBIYRr8Q/o/a0ber0UPy9BVWeCmShshWCA2WkhdiCYrZTEt7yQNoBAv8pnJFu5FYlV0avTRfE+iKQB+8Cqa5TutBnjHTkpNlVjSaALwDquGyBywrYqqf64jtUq3Cnp3xuYPFXxSRAwQ63xSC0LN6U9vlgEgi6GtHNXc/qM6zIrHcRA1ZEUzMGNSmn6rkeZiZL6v9GnoFOk7pn+uFliI1E0OqJGbSekp877faBUXc/vQqJ35ocoDA72+3FiPkbBIW0pkCnyNKMs04t1hKNMW7iCZGJP/1L8EJgh5QrcbwpaQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=fb.com; dmarc=pass action=none header.from=fb.com; dkim=pass header.d=fb.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; s=selector2-fb-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=yLk0GexK0V0FQxZdUTnIFAmr0rIG5UcSsYqOwP0pgGw=; b=dxXjrtptF1g2k9PJLdjsA1jiZWmagy44nc0YtWTT5xAbFjYBGofuBVqli1RQREWGRWvfMSXWKJFqSQ9uKwoHDOMbjsEZFm6ZVjlCQSDWnXcfnINg3xG9pWIv4rPnbY855rYRcptCBHok7DsMBWr213DhXedWbBWYDvFqB+URXtE= Received: from BYAPR15MB2999.namprd15.prod.outlook.com (2603:10b6:a03:fa::12) by BYAPR15MB2246.namprd15.prod.outlook.com (2603:10b6:a02:8d::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3721.23; Tue, 5 Jan 2021 05:47:34 +0000 Received: from BYAPR15MB2999.namprd15.prod.outlook.com ([fe80::c97:58e4:ee9:1dc0]) by BYAPR15MB2999.namprd15.prod.outlook.com ([fe80::c97:58e4:ee9:1dc0%7]) with mapi id 15.20.3721.024; Tue, 5 Jan 2021 05:47:34 +0000 From: Song Liu To: Alexei Starovoitov CC: Yonghong Song , "bpf@vger.kernel.org" , "netdev@vger.kernel.org" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "john.fastabend@gmail.com" , "kpsingh@chromium.org" , Kernel Team Subject: Re: [PATCH v2 bpf-next 1/4] bpf: introduce task_vma bpf_iter Thread-Topic: [PATCH v2 bpf-next 1/4] bpf: introduce task_vma bpf_iter Thread-Index: AQHW0zs42cd9AcJBNEyi77fZmX7Jx6n7qAwAgAAzywCAAEpiAIAAIRcAgAAOLwCAALyEgIAADIEAgBtELICAAENfgA== Date: Tue, 5 Jan 2021 05:47:34 +0000 Message-ID: <6E122A14-0F77-46F9-8891-EDF4DB494E37@fb.com> References: <20201215233702.3301881-1-songliubraving@fb.com> <20201215233702.3301881-2-songliubraving@fb.com> <20201217190308.insbsxpf6ujapbs3@ast-mbp> <20201218023444.i6hmdi3bp5vgxou2@ast-mbp> <231d0521-62a7-427b-5351-359092e73dde@fb.com> <09DA43B9-0F6F-45C1-A60D-12E61493C71F@fb.com> <20210105014625.krtz3uzqtfu4y7m5@ast-mbp> In-Reply-To: <20210105014625.krtz3uzqtfu4y7m5@ast-mbp> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.120.23.2.4) authentication-results: gmail.com; dkim=none (message not signed) header.d=none;gmail.com; dmarc=none action=none header.from=fb.com; x-originating-ip: [2620:10d:c090:400::5:4dc5] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 6a4d6cbb-3dc0-43bf-daf6-08d8b13d66a0 x-ms-traffictypediagnostic: BYAPR15MB2246: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:10000; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 6mC96y+MzWFUQj5JyGEdzLHBHKa69rYRtoZWd5lGraWukEJQ8QYo394D/8l7aOOVvt7G0YVotvWmzxVaUwjuSz85Rb2nHJ8lhunx3UOemW3sb6mjIeMEL2mmIBW/erCn961UVKoQMv3/Oxh6h6RC01izP4NSx0ifmB9UkKWaf9Zun8ABhAmsZJpnks/Nq8mv0PoiCKSzUqKZiASYN0dFcHeeAAyuLLOIS0ay7VojatBXdDRoQIHxaeGNETTjT8nhWUqAlPooX66C+rxF6KFD/wU0nBlJxQ81CIgjC3DC6v9bJA1VDZ0rMloBoSxbyuMb43KnM53wmYSH7iZiZr7o7z+nbvW7mPOTsHE44WU12Izi28JrA5v14CE7pcW+VEtNLJNyz5Bqy52ZDjPxb8543eYSa8eT35oqxPlRq75vUNrQCvSENeWHHHR+3/JbhHcK x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR15MB2999.namprd15.prod.outlook.com;PTR:;CAT:NONE;SFS:(136003)(376002)(366004)(346002)(396003)(39860400002)(186003)(53546011)(478600001)(54906003)(33656002)(6512007)(71200400001)(86362001)(4326008)(6506007)(66556008)(66446008)(64756008)(2906002)(316002)(66946007)(91956017)(66476007)(36756003)(8676002)(6916009)(2616005)(5660300002)(83380400001)(6486002)(76116006)(8936002)(45980500001);DIR:OUT;SFP:1102; x-ms-exchange-antispam-messagedata: =?us-ascii?Q?Aqo8Bk5QgAFB++jCo9vkVFAHhtIbTtBbTcyvEB8ks3t1yoL8uCIM0uP8ksFZ?= =?us-ascii?Q?dnvPaKBZJfCuAjErc3qChS8z2LrAk+DvZ5j7oPdEWGIcgNxMp4OJP+ewWLes?= =?us-ascii?Q?YvSDSxyKU/4leoLpx2Zd1aJWmHH5mcCY9fhMAwIeK/GMEcneuZI8qnn+Hnic?= =?us-ascii?Q?k/lxupVR+sw73PsheyFQDVKXI3I7ByuYh2XWOgxrglngM9gkhF5kwWnvrZXM?= =?us-ascii?Q?8e4B2hUxaXXTmNY7oeIUJ6n16gYP/bkS4FtZspYuohBkeavNCbT+As4h684+?= =?us-ascii?Q?6si1qxMneEaTPb/oFhSXX8iFG6e+lRkPefDaob6M38lM8oREVCNG5fIBA/bb?= =?us-ascii?Q?Ny755qN1SP/dN+3YhaRpjo23hrKllkFrvw3IgMl+cm9KPXnyta50o6LBe2VB?= =?us-ascii?Q?8TpKExL6aaslARBCJbMzxfHL9Ta02fHHe5ybLsprz7g7q99XmmZHfQXAtjBv?= =?us-ascii?Q?YnsAgrNazNWE3FGaOJjLtoNax5Rga7hnQ1gndlKUcnxjje1doUv+moINzo0D?= =?us-ascii?Q?E+HgT0eP10DygVVJosie7jNZXC9gNbzb6ZD1zjkosKb4TOWwy9QdeznnOom7?= =?us-ascii?Q?+BJC2FbQSdHmz/fBHBY5Q3pM3mwj5YI9+3uRjqex2Y2LN21o48kYAshVDf2D?= =?us-ascii?Q?a91zAo5G7/pwlb+svCFgmCRpZeind19gTfaOY4CDkXB6amuY5IRLf7+uHxcu?= =?us-ascii?Q?qdCmsNIVROirr2F5m0qml0JYI3rUsgRdBDvhQaaA09pPO/3e0I38CIcYa+v4?= =?us-ascii?Q?1KnFmaRqM7cQRV/waJJXi5kK5h+La3G/0+vP4A/r9M2CpzuV1RStzeM/CW0h?= =?us-ascii?Q?JVsxJEdpS64dkwDws0/T0+DFLW7cf5JUxbO2Bgf2QJv+YTq0Qukp7Hkhn3Vs?= =?us-ascii?Q?xvwpWaqO/GLkDyUYVFjvgeg+R3ndZsSB9yZeQXNlZYkRnG+Il5zkyaOOmxTP?= =?us-ascii?Q?1DQhXqJDMJ+DnkWt1CI9EgmVI2YxpGEGbz7ZcLsGb1v6G79J2NupRCkd9WSF?= =?us-ascii?Q?yLSjjUg/xkq2EbVPqvEpbz3u8ID8u8ct8fIr3IY/oNAxsWw=3D?= Content-Type: text/plain; charset="us-ascii" Content-ID: <25AE158875720849B0808DE9FC997B5A@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB2999.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6a4d6cbb-3dc0-43bf-daf6-08d8b13d66a0 X-MS-Exchange-CrossTenant-originalarrivaltime: 05 Jan 2021 05:47:34.4025 (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: GoxcWlC3BlK/7R1aViGy0R3UTXBDZlvzF+Suxz0U60FTX9jeM0VPzsEQh1wkpvwc7dCgkBl8NU5bSAyIloxv3w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2246 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-05_01:2021-01-04,2021-01-05 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 adultscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 mlxlogscore=999 mlxscore=0 phishscore=0 lowpriorityscore=0 suspectscore=0 clxscore=1015 spamscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101050035 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > On Jan 4, 2021, at 5:46 PM, Alexei Starovoitov wrote: >=20 > On Fri, Dec 18, 2020 at 05:23:25PM +0000, Song Liu wrote: >>=20 >>=20 >>> On Dec 18, 2020, at 8:38 AM, Yonghong Song wrote: >>>=20 >>>=20 >>>=20 >>> On 12/17/20 9:23 PM, Alexei Starovoitov wrote: >>>> On Thu, Dec 17, 2020 at 8:33 PM Song Liu wrote= : >>>>>>=20 >>>>>> ahh. I missed that. Makes sense. >>>>>> vm_file needs to be accurate, but vm_area_struct should be accessed = as ptr_to_btf_id. >>>>>=20 >>>>> Passing pointer of vm_area_struct into BPF will be tricky. For exampl= e, shall we >>>>> allow the user to access vma->vm_file? IIUC, with ptr_to_btf_id the v= erifier will >>>>> allow access of vma->vm_file as a valid pointer to struct file. Howev= er, since the >>>>> vma might be freed, vma->vm_file could point to random data. >>>> I don't think so. The proposed patch will do get_file() on it. >>>> There is actually no need to assign it into a different variable. >>>> Accessing it via vma->vm_file is safe and cleaner. >>>=20 >>> I did not check the code but do you have scenarios where vma is freed b= ut old vma->vm_file is not freed due to reference counting, but >>> freed vma area is reused so vma->vm_file could be garbage? >>=20 >> AFAIK, once we unlock mmap_sem, the vma could be freed and reused. I gue= ss ptr_to_btf_id >> or probe_read would not help with this? >=20 > Theoretically we can hack the verifier to treat some ptr_to_btf_id as "le= ss > valid" than the other ptr_to_btf_id, but the user experience will not be = great. > Reading such bpf prog will not be obvious. I think it's better to run bpf= prog > in mmap_lock then and let it access vma->vm_file. After prog finishes the= iter > bit can do if (mmap_lock_is_contended()) before iterating. That will deli= ver > better performance too. Instead of task_vma_seq_get_next() doing > mmap_lock/unlock at every vma. No need for get_file() either. And no > __vm_area_struct exposure. I think there might be concern calling BPF program with mmap_lock, especial= ly that=20 the program is sleepable (for bpf_d_path). It shouldn't be a problem for co= mmon=20 cases, but I am not 100% sure for corner cases (many instructions in BPF + = sleep).=20 Current version is designed to be very safe for the workload, which might b= e too conservative.=20 Thanks, Song