From patchwork Tue Jan 19 15:35:18 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yonghong Song X-Patchwork-Id: 12030203 X-Patchwork-Delegate: bpf@iogearbox.net 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=-18.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham 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 5C462C433DB for ; Tue, 19 Jan 2021 15:43:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CA7E23139 for ; Tue, 19 Jan 2021 15:43:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391111AbhASPnE (ORCPT ); Tue, 19 Jan 2021 10:43:04 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:9670 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389991AbhASPgJ (ORCPT ); Tue, 19 Jan 2021 10:36:09 -0500 Received: from pps.filterd (m0148461.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 10JFWx6i010109 for ; Tue, 19 Jan 2021 07:35:22 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : content-type : content-transfer-encoding : mime-version; s=facebook; bh=uVPBmzR+FnTbFvxqeQzOTybg2DWGiKxlEDuUr8uELO0=; b=EAe+9pLJTGGq95+it8IWGOT9/dSGHvSilOJbTbGICcXVXC5nb4oVnF5qxmojsDf2Kp0M bIjFwawTmxpVpk8xCy02xUTqV2/txEm38Bk9Ut3cjQqMEMKmWbONWadMOECn3Jk/K4cz QejosmBLmGZ1QtRoA7/Rm73LLc9+zX0Zz+Y= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 364h3bhnbn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 19 Jan 2021 07:35:22 -0800 Received: from intmgw001.03.ash8.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Tue, 19 Jan 2021 07:35:20 -0800 Received: by devbig003.ftw2.facebook.com (Postfix, from userid 128203) id 0D74C37014B4; Tue, 19 Jan 2021 07:35:19 -0800 (PST) From: Yonghong Song To: CC: Alexei Starovoitov , Daniel Borkmann , Subject: [PATCH bpf-next] bpf: permit size-0 datasec Date: Tue, 19 Jan 2021 07:35:18 -0800 Message-ID: <20210119153519.3901963-1-yhs@fb.com> X-Mailer: git-send-email 2.24.1 X-FB-Internal: Safe X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-19_05:2021-01-18,2021-01-19 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 clxscore=1015 suspectscore=0 spamscore=0 malwarescore=0 impostorscore=0 priorityscore=1501 phishscore=0 mlxscore=0 bulkscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101190094 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net llvm patch https://reviews.llvm.org/D84002 permitted to emit empty rodata datasec if the elf .rodata section contains read-only data from local variables. These local variables will be not emitted as BTF_KIND_VARs since llvm converted these local variables as static variables with private linkage without debuginfo types. Such an empty rodata datasec will make skeleton code generation easy since for skeleton a rodata struct will be generated if there is a .rodata elf section. The existence of a rodata btf datasec is also consistent with the existence of a rodata map created by libbpf. The btf with such an empty rodata datasec will fail in the kernel though as kernel will reject a datasec with zero vlen and zero size. For example, for the below code, int sys_enter(void *ctx) { int fmt[6] = {1, 2, 3, 4, 5, 6}; int dst[6]; bpf_probe_read(dst, sizeof(dst), fmt); return 0; } We got the below btf (bpftool btf dump ./test.o): [1] PTR '(anon)' type_id=0 [2] FUNC_PROTO '(anon)' ret_type_id=3 vlen=1 'ctx' type_id=1 [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED [4] FUNC 'sys_enter' type_id=2 linkage=global [5] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED [6] ARRAY '(anon)' type_id=5 index_type_id=7 nr_elems=4 [7] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none) [8] VAR '_license' type_id=6, linkage=global-alloc [9] DATASEC '.rodata' size=0 vlen=0 [10] DATASEC 'license' size=0 vlen=1 type_id=8 offset=0 size=4 When loading the ./test.o to the kernel with bpftool, we see the following error: libbpf: Error loading BTF: Invalid argument(22) libbpf: magic: 0xeb9f ... [6] ARRAY (anon) type_id=5 index_type_id=7 nr_elems=4 [7] INT __ARRAY_SIZE_TYPE__ size=4 bits_offset=0 nr_bits=32 encoding=(none) [8] VAR _license type_id=6 linkage=1 [9] DATASEC .rodata size=24 vlen=0 vlen == 0 libbpf: Error loading .BTF into kernel: -22. BTF is optional, ignoring. Basically, libbpf changed .rodata datasec size to 24 since elf .rodata section size is 24. The kernel then rejected the BTF since vlen = 0. Note that the above kernel verifier failure can be worked around with changing local variable "fmt" to a static or global, optionally const, variable. This patch permits a datasec with vlen = 0 in kernel. Signed-off-by: Yonghong Song --- kernel/bpf/btf.c | 5 ----- tools/testing/selftests/bpf/prog_tests/btf.c | 21 ++++++++++++++++++++ 2 files changed, 21 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 7ccc0133723a..71e6c2fa4830 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3540,11 +3540,6 @@ static s32 btf_datasec_check_meta(struct btf_verifier_env *env, return -EINVAL; } - if (!btf_type_vlen(t)) { - btf_verifier_log_type(env, t, "vlen == 0"); - return -EINVAL; - } - if (!t->size) { btf_verifier_log_type(env, t, "size == 0"); return -EINVAL; diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c index 8ae97e2a4b9d..055d2c0486ed 100644 --- a/tools/testing/selftests/bpf/prog_tests/btf.c +++ b/tools/testing/selftests/bpf/prog_tests/btf.c @@ -3509,6 +3509,27 @@ static struct btf_raw_test raw_tests[] = { .value_type_id = 3 /* arr_t */, .max_entries = 4, }, +/* + * elf .rodata section size 4 and btf .rodata section vlen 0. + */ +{ + .descr = "datasec: vlen == 0", + .raw_types = { + /* int */ + BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */ + /* .rodata section */ + BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 0), 4), + /* [2] */ + BTF_END_RAW, + }, + BTF_STR_SEC("\0.rodata"), + .map_type = BPF_MAP_TYPE_ARRAY, + .key_size = sizeof(int), + .value_size = sizeof(int), + .key_type_id = 1, + .value_type_id = 1, + .max_entries = 1, +}, }; /* struct btf_raw_test raw_tests[] */