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Sun, 10 May 2020 05:18:39 +0000 Subject: Re: [PATCH bpf-next v4 12/21] bpf: add PTR_TO_BTF_ID_OR_NULL support To: Alexei Starovoitov CC: Andrii Nakryiko , , Martin KaFai Lau , , Alexei Starovoitov , Daniel Borkmann , References: <20200509175859.2474608-1-yhs@fb.com> <20200509175912.2476576-1-yhs@fb.com> <20200510005059.d3zocagerrnsspez@ast-mbp> From: Yonghong Song Message-ID: Date: Sat, 9 May 2020 22:18:37 -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: <20200510005059.d3zocagerrnsspez@ast-mbp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR06CA0014.namprd06.prod.outlook.com (2603:10b6:a03:d4::27) 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:e956) by BYAPR06CA0014.namprd06.prod.outlook.com (2603:10b6:a03:d4::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2979.28 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: ce826c4b-2008-4e00-b3c1-08d7f4a19924 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 May 2020 05:18:39.4094 (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: USm0lpKi+cU6ATcBahwp+AtY6d2SVTSMePYzgjf2x2mrUoGZO7MVS7zdP+MiCq6p X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3349 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.676 definitions=2020-05-10_01:2020-05-08,2020-05-10 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 bulkscore=0 adultscore=0 clxscore=1015 mlxscore=0 spamscore=0 impostorscore=0 phishscore=0 lowpriorityscore=0 mlxlogscore=999 priorityscore=1501 suspectscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005100048 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 5/9/20 5:50 PM, Alexei Starovoitov wrote: > On Sat, May 09, 2020 at 10:59:12AM -0700, Yonghong Song wrote: >> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c >> index a2cfba89a8e1..c490fbde22d4 100644 >> --- a/kernel/bpf/btf.c >> +++ b/kernel/bpf/btf.c >> @@ -3790,7 +3790,10 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, >> return true; >> >> /* this is a pointer to another type */ >> - info->reg_type = PTR_TO_BTF_ID; >> + if (off != 0 && prog->aux->btf_id_or_null_non0_off) >> + info->reg_type = PTR_TO_BTF_ID_OR_NULL; >> + else >> + info->reg_type = PTR_TO_BTF_ID; > > I think the verifier should be smarter than this. > It's too specific and inflexible. All ctx fields of bpf_iter execpt first > will be such ? let's figure out a different way to tell verifier about this. > How about using typedef with specific suffix? Like: > typedef struct bpf_map *bpf_map_or_null; > struct bpf_iter__bpf_map { > struct bpf_iter_meta *meta; > bpf_map_or_null map; > }; > or use a union with specific second member? Like: > struct bpf_iter__bpf_map { > struct bpf_iter_meta *meta; > union { > struct bpf_map *map; > long null; > }; > }; I have an alternative approach to refactor this for future support for map elements as well. For example, for bpf_map_elements iterator the prog context type can be struct bpf_iter_bpf_map_elem { struct bpf_iter_meta *meta; strruct bpf_map *map; *key; *val; }; target will pass the following information to bpf_iter registration: arg 1: PTR_TO_BTF_ID arg 2: PTR_TO_BTF_ID_OR_NULL arg 3: PTR_TO_BUFFER arg 4: PTR_TO_BUFFER verifier will retrieve the reg_type from target.