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Wed, 29 Apr 2020 01:27:36 +0000 Subject: Re: [PATCH bpf-next v1 04/19] bpf: allow loading of a bpf_iter program To: Martin KaFai Lau CC: Andrii Nakryiko , , , Alexei Starovoitov , Daniel Borkmann , References: <20200427201235.2994549-1-yhs@fb.com> <20200427201239.2994896-1-yhs@fb.com> <20200429005415.x2ocuctowbagpkaw@kafai-mbp> From: Yonghong Song Message-ID: Date: Tue, 28 Apr 2020 18:27:32 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 In-Reply-To: <20200429005415.x2ocuctowbagpkaw@kafai-mbp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW2PR16CA0059.namprd16.prod.outlook.com (2603:10b6:907:1::36) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from macbook-pro-52.local.dhcp.thefacebook.com (2620:10d:c090:400::5:2258) by MW2PR16CA0059.namprd16.prod.outlook.com (2603:10b6:907:1::36) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2958.19 via Frontend Transport; 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The load attribute >> attach_btf_id >> is used by the verifier against a particular kernel function, >> e.g., __bpf_iter__bpf_map in our previous bpf_map iterator. >> >> The program return value must be 0 for now. In the >> future, other return values may be used for filtering or >> teminating the iterator. >> >> Signed-off-by: Yonghong Song >> --- >> include/uapi/linux/bpf.h | 1 + >> kernel/bpf/verifier.c | 20 ++++++++++++++++++++ >> tools/include/uapi/linux/bpf.h | 1 + >> 3 files changed, 22 insertions(+) >> >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >> index 4a6c47f3febe..f39b9fec37ab 100644 >> --- a/include/uapi/linux/bpf.h >> +++ b/include/uapi/linux/bpf.h >> @@ -215,6 +215,7 @@ enum bpf_attach_type { >> BPF_TRACE_FEXIT, >> BPF_MODIFY_RETURN, >> BPF_LSM_MAC, >> + BPF_TRACE_ITER, >> __MAX_BPF_ATTACH_TYPE >> }; >> >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index 91728e0f27eb..fd36c22685d9 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -7074,6 +7074,11 @@ static int check_return_code(struct bpf_verifier_env *env) >> return 0; >> range = tnum_const(0); >> break; >> + case BPF_PROG_TYPE_TRACING: >> + if (env->prog->expected_attach_type != BPF_TRACE_ITER) >> + return 0; >> + range = tnum_const(0); >> + break; >> default: >> return 0; >> } >> @@ -10454,6 +10459,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) >> struct bpf_prog *tgt_prog = prog->aux->linked_prog; >> u32 btf_id = prog->aux->attach_btf_id; >> const char prefix[] = "btf_trace_"; >> + struct btf_func_model fmodel; >> int ret = 0, subprog = -1, i; >> struct bpf_trampoline *tr; >> const struct btf_type *t; >> @@ -10595,6 +10601,20 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) >> prog->aux->attach_func_proto = t; >> prog->aux->attach_btf_trace = true; >> return 0; >> + case BPF_TRACE_ITER: >> + if (!btf_type_is_func(t)) { >> + verbose(env, "attach_btf_id %u is not a function\n", >> + btf_id); >> + return -EINVAL; >> + } >> + t = btf_type_by_id(btf, t->type); >> + if (!btf_type_is_func_proto(t)) > Other than the type tests, > to ensure the attach_btf_id is a supported bpf_iter target, > should the prog be checked against the target list > ("struct list_head targets") here also during the prog load time? This is a good question. In my RFC v2, I did this, checking against registered targets (essentially, program loading + attaching to the target). In this version, program loading and attaching are separated. - program loading: against btf_id - attaching: linking bpf program to target current linking parameter only bpf_program, but later on there may be additional parameters like map_id, pid, cgroup_id etc. for tailoring the iterator behavior. This seems having a better separation. Agreed that checking at load time may return error earlier instead at link_create time. Let me think about this. > >> + return -EINVAL; >> + prog->aux->attach_func_name = tname; >> + prog->aux->attach_func_proto = t; >> + ret = btf_distill_func_proto(&env->log, btf, t, >> + tname, &fmodel); >> + return ret; >> default: >> if (!prog_extension) >> return -EINVAL;