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Tue, 12 Jan 2021 01:25:19 +0000 Subject: Re: [PATCH v2 bpf-next 5/7] bpf: support BPF ksym variables in kernel modules To: Andrii Nakryiko CC: Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team , Hao Luo References: <20210108220930.482456-1-andrii@kernel.org> <20210108220930.482456-6-andrii@kernel.org> From: Yonghong Song Message-ID: Date: Mon, 11 Jan 2021 17:25:17 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:7b7c] X-ClientProxiedBy: BYAPR05CA0084.namprd05.prod.outlook.com (2603:10b6:a03:e0::25) 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:c085:21e1::190b] (2620:10d:c090:400::5:7b7c) by BYAPR05CA0084.namprd05.prod.outlook.com (2603:10b6:a03:e0::25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3763.2 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?Rjg4OS9zYjNzYkJqR1NKQUhMSktrZjUvVzUvbndZUFVZS2YwZkZFckt0eE1T?= =?utf-8?B?WVhUS3hJZFpXOUl6by9oLy9PTFpYVXh3MFp3TlRtVzhFUmVPbGZXWjllSktF?= =?utf-8?B?ZFBiUXlFcHR0N0paTlh0VjhXU1RlSFRNV2xzV3ZHakxZNVRyYk4wZ2s2SDhL?= =?utf-8?B?SEYxSExQeDJpSGlCdzFQWjhRTWVVSGJpekNMNGM1WlJmdXpWWUtqSU5MVkVN?= =?utf-8?B?cjQ2VU52dnJrVWM0K2VlWndaL3VNckNPTFU3VG94VTZsVEJ6ay8zdFBzS05S?= =?utf-8?B?Z3hibk9hd2FUUHZBZWw2MFhNWFBhVi9xckNBTmhxTFdQTWpaZFdlTUFVbUFU?= =?utf-8?B?NzNZQzl0bDVYNDhJZ2VJVWdsRzZwNFBnckp6Zk1RTnhTbzB6MkFrSnZvcVdk?= =?utf-8?B?OXRqbmROcWtyL2RPRWh2dXZjRnFZZVZiTktxNmtNQ2piem9sM2hpV2hBNlI4?= =?utf-8?B?UUNFQ0hTaTdWNmR5TDFjY0VUa1VuYXlFanpnS0xtbFc5Y0M4REExRmpTRnpU?= =?utf-8?B?ZUxBdTkxd3AzSi8vS293cGZMT2Nabm8wdDd2ZVF1YVptaUdHNVR0SnBQbE1E?= =?utf-8?B?LzN6ZnVGRS95NDJaTHNWNmJHUklKWDkxZEtYQ0V1NmVrYVlybVFlVHV2aytU?= =?utf-8?B?ZUVzdHJVZ2dMY0MvUnpUSGpmejY0WVRoWDc4OHh1SXJhekpvdGd4aDgyUFhK?= =?utf-8?B?V0dkRC9SRm9IRzVVamlOV3I4ZU9mVXFBS1VEL1lRTzRCNHlDcXN5eVlEYUJS?= =?utf-8?B?RTZzWVVsN1NNc0lnUXMzOGplcEt0TzI5M1VrZDYwQ0VlWi9Cbk5waERSL3Z4?= =?utf-8?B?THJYeXRFSzVFMm1sOU8vMk9sOHhnekJ0RkI0RE1jVWtFV2RlTDFrYldyOWNx?= =?utf-8?B?ak04d01yTXVzTzFoTVd0bUFOQnM4K3NHYU9GUE5vTlpsRnZyeU9xT3p6a1Vm?= =?utf-8?B?UXVYa0dHZWVSeTRUVkVzTS92SmZmMExGWS9BbnRwWURnMm5BVHF0VUpybGhk?= =?utf-8?B?RGtwblNXZGRpKzBoWUJRMGpxTHNENWcvZ2ZKd0M1YkRNdmdDWm03WG9VWkox?= =?utf-8?B?MVZxb1dqa0lZNkszTjgxRktjZWVocDhEN2RUMmhWUjBNdFpBb1g2NFl1SUEv?= =?utf-8?B?NjdENkQ0VUF3a2JoZnJWdEQ5MUlieXpjV2hxWEdLWDlwWmJ1ZjUyOS8vVlVw?= =?utf-8?B?MUFPbEdWWDNqM2YvZWZZV2VJTW5jZHVlUSt2L0MyWWhBTDlvcVd1c2RyeHhW?= =?utf-8?B?RU1pbWRMR3hJVGt6QU16QnR2QjNQU2wzdVhya01pa1lEMlkxVXcyMFlNdkZC?= =?utf-8?B?OUtrcytHR2pXb0RXejNyRFZGaDhUSGwyUVhySE95aUFTVTg0RURTZmduNW9R?= =?utf-8?B?Y3BIa2JMVHJCZWc9PQ==?= X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jan 2021 01:25:19.2005 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-Network-Message-Id: 9aa13622-8284-4b85-0299-08d8b698ec8f X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: wcdChA7ps9/V/DW9msI80Zdhc+suWfJ3UUBS7HQlE1+o55VI5ngoKuIwHNbMDZpV X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3302 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-11_34:2021-01-11,2021-01-11 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 phishscore=0 priorityscore=1501 suspectscore=0 clxscore=1015 malwarescore=0 bulkscore=0 impostorscore=0 lowpriorityscore=0 mlxlogscore=999 adultscore=0 spamscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101120003 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 1/11/21 1:29 PM, Andrii Nakryiko wrote: > On Sun, Jan 10, 2021 at 8:13 PM Yonghong Song wrote: >> >> >> >> On 1/8/21 2:09 PM, Andrii Nakryiko wrote: >>> Add support for directly accessing kernel module variables from BPF programs >>> using special ldimm64 instructions. This functionality builds upon vmlinux >>> ksym support, but extends ldimm64 with src_reg=BPF_PSEUDO_BTF_ID to allow >>> specifying kernel module BTF's FD in insn[1].imm field. >>> >>> During BPF program load time, verifier will resolve FD to BTF object and will >>> take reference on BTF object itself and, for module BTFs, corresponding module >>> as well, to make sure it won't be unloaded from under running BPF program. The >>> mechanism used is similar to how bpf_prog keeps track of used bpf_maps. >>> >>> One interesting change is also in how per-CPU variable is determined. The >>> logic is to find .data..percpu data section in provided BTF, but both vmlinux >>> and module each have their own .data..percpu entries in BTF. So for module's >>> case, the search for DATASEC record needs to look at only module's added BTF >>> types. This is implemented with custom search function. >>> >>> Signed-off-by: Andrii Nakryiko >> >> Ack with a minor nit below. >> >> Acked-by: Yonghong Song >> >>> --- >>> include/linux/bpf.h | 10 +++ >>> include/linux/bpf_verifier.h | 3 + >>> include/linux/btf.h | 3 + >>> kernel/bpf/btf.c | 31 +++++++- >>> kernel/bpf/core.c | 23 ++++++ >>> kernel/bpf/verifier.c | 149 ++++++++++++++++++++++++++++------- >>> 6 files changed, 189 insertions(+), 30 deletions(-) >>> >> [...] >>> /* replace pseudo btf_id with kernel symbol address */ >>> static int check_pseudo_btf_id(struct bpf_verifier_env *env, >>> struct bpf_insn *insn, > > [...] > >>> } else { >>> aux->btf_var.reg_type = PTR_TO_BTF_ID; >>> - aux->btf_var.btf = btf_vmlinux; >>> + aux->btf_var.btf = btf; >>> aux->btf_var.btf_id = type; >>> } >>> + >>> + /* check whether we recorded this BTF (and maybe module) already */ >>> + for (i = 0; i < env->used_btf_cnt; i++) { >>> + if (env->used_btfs[i].btf == btf) { >>> + btf_put(btf); >>> + return 0; >> >> An alternative way is to change the above code as >> err = 0; >> goto err_put; > > I didn't do it, because it's not really an error case, which err_put > implies. If in the future we'll have some more clean up to do, it > might make sense, I suppose. You can change label err_put to btf_put, so this way, btf_put() will only show up in one place. But I won't insist on this. > >> >>> + } >>> + } >>> + >>> + if (env->used_btf_cnt >= MAX_USED_BTFS) { >>> + err = -E2BIG; >>> + goto err_put; >>> + } >>> + >>> + btf_mod = &env->used_btfs[env->used_btf_cnt]; >>> + btf_mod->btf = btf; >>> + btf_mod->module = NULL; >>> + >>> + /* if we reference variables from kernel module, bump its refcount */ >>> + if (btf_is_module(btf)) { >>> + btf_mod->module = btf_try_get_module(btf); >>> + if (!btf_mod->module) { >>> + err = -ENXIO; >>> + goto err_put; >>> + } >>> + } >>> + >>> + env->used_btf_cnt++; >>> + >>> return 0; >>> +err_put: >>> + btf_put(btf); >>> + return err; >>> } >>> >> [...]