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Tue, 12 May 2020 16:29:08 +0000 Subject: Re: [PATCH bpf-next v4 02/21] bpf: allow loading of a bpf_iter program To: Alexei Starovoitov CC: Andrii Nakryiko , , Martin KaFai Lau , , Alexei Starovoitov , Daniel Borkmann , References: <20200509175859.2474608-1-yhs@fb.com> <20200509175900.2474947-1-yhs@fb.com> <20200510004139.tjlll6wqq7zevb73@ast-mbp> <20200512162524.4yq4i3or4wtwl43x@ast-mbp> From: Yonghong Song Message-ID: <754bce5b-bb4f-69f0-f938-2de3fd4d56ef@fb.com> Date: Tue, 12 May 2020 09:29:05 -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: <20200512162524.4yq4i3or4wtwl43x@ast-mbp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR21CA0030.namprd21.prod.outlook.com (2603:10b6:a03:114::40) 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:d0f0) by BYAPR21CA0030.namprd21.prod.outlook.com (2603:10b6:a03:114::40) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3021.2 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: e689f652-1866-4380-78b4-08d7f6919809 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 May 2020 16:29:07.9761 (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: k8fHz+dniPI8sXI5RZ8kwwP+5S5RBun3zILRYiBlEmQjOaM/K5Y/0bDunYuIYel8 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2245 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.676 definitions=2020-05-12_05:2020-05-11,2020-05-12 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 spamscore=0 impostorscore=0 suspectscore=0 adultscore=0 phishscore=0 bulkscore=0 clxscore=1015 malwarescore=0 mlxlogscore=999 priorityscore=1501 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005120126 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 5/12/20 9:25 AM, Alexei Starovoitov wrote: > On Tue, May 12, 2020 at 08:41:19AM -0700, Yonghong Song wrote: >> >> >> On 5/9/20 5:41 PM, Alexei Starovoitov wrote: >>> On Sat, May 09, 2020 at 10:59:00AM -0700, Yonghong Song wrote: >>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >>>> index 70ad009577f8..d725ff7d11db 100644 >>>> --- a/kernel/bpf/verifier.c >>>> +++ b/kernel/bpf/verifier.c >>>> @@ -7101,6 +7101,10 @@ 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; >>>> + break; >>> >>> Not related to this set, but I just noticed that I managed to forget to >>> add this check for fentry/fexit/freplace. >>> While it's not too late let's enforce return 0 for them ? >>> Could you follow up with a patch for bpf tree? >> >> Just want to double check. In selftests, we have >> >> SEC("fentry/__set_task_comm") >> int BPF_PROG(prog4, struct task_struct *tsk, const char *buf, bool exec) >> { >> return !tsk; >> } >> >> SEC("fexit/__set_task_comm") >> int BPF_PROG(prog5, struct task_struct *tsk, const char *buf, bool exec) >> { >> return !tsk; >> } >> >> fentry/fexit may returrn 1. What is the intention here? Does this mean >> we should allow [0, 1] instead of [0, 0]? > > Argh. I missed that bit when commit ac065870d9282 tweaked the return > value. For fentry/exit the return value is ignored by trampoline. > imo it's misleading to users and should be rejected by the verifier. > so [0,0] for fentry/fexit Sounds good. Will craft patch to enforce fentry/fexit with [0,0] then. Thanks! > >> For freplace, we have >> >> __u64 test_get_skb_len = 0; >> SEC("freplace/get_skb_len") >> int new_get_skb_len(struct __sk_buff *skb) >> { >> int len = skb->len; >> >> if (len != 74) >> return 0; >> test_get_skb_len = 1; >> return 74; /* original get_skb_len() returns skb->len */ >> } >> >> That means freplace may return arbitrary values depending on what >> to replace? > > yes. freplace and fmod_ret can return anything. >