From mboxrd@z Thu Jan 1 00:00:00 1970 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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 56600CA9EC0 for ; Mon, 28 Oct 2019 12:29:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3317220717 for ; Mon, 28 Oct 2019 12:29:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389070AbfJ1M3Y (ORCPT ); Mon, 28 Oct 2019 08:29:24 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:28708 "EHLO mx0b-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727503AbfJ1M3X (ORCPT ); Mon, 28 Oct 2019 08:29:23 -0400 Received: from pps.filterd (m0127361.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x9SCRmfu136956 for ; Mon, 28 Oct 2019 08:29:22 -0400 Received: from e06smtp02.uk.ibm.com (e06smtp02.uk.ibm.com [195.75.94.98]) by mx0a-001b2d01.pphosted.com with ESMTP id 2vvgy37km4-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 28 Oct 2019 08:29:21 -0400 Received: from localhost by e06smtp02.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 28 Oct 2019 12:29:19 -0000 Received: from b06cxnps4076.portsmouth.uk.ibm.com (9.149.109.198) by e06smtp02.uk.ibm.com (192.168.101.132) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 28 Oct 2019 12:29:16 -0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x9SCTEwu41943278 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 28 Oct 2019 12:29:14 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D098C11C05B; Mon, 28 Oct 2019 12:29:14 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8237311C054; Mon, 28 Oct 2019 12:29:14 +0000 (GMT) Received: from white.boeblingen.de.ibm.com (unknown [9.152.97.44]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 28 Oct 2019 12:29:14 +0000 (GMT) From: Ilya Leoshkevich To: Daniel Borkmann , Alexei Starovoitov Cc: bpf@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Andrey Ignatov , Ilya Leoshkevich Subject: [PATCH bpf] bpf: allow narrow loads of bpf_sysctl fields with offset > 0 Date: Mon, 28 Oct 2019 13:29:02 +0100 X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19102812-0008-0000-0000-0000032860AF X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19102812-0009-0000-0000-00004A479EA4 Message-Id: <20191028122902.9763-1-iii@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-10-28_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910280128 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org "ctx:file_pos sysctl:read read ok narrow" works on s390 by accident: it reads the wrong byte, which happens to have the expected value of 0. Improve the test by seeking to the 4th byte and expecting 4 instead of 0. This makes the latent problem apparent: the test attempts to read the first byte of bpf_sysctl.file_pos, assuming this is the least-significant byte, which is not the case on big-endian machines: a non-zero offset is needed. The point of the test is to verify narrow loads, so we cannot cheat our way out by simply using BPF_W. The existence of the test means that such loads have to be supported, most likely because llvm can generate them. Fix the test by adding a big-endian variant, which uses an offset to access the least-significant byte of bpf_sysctl.file_pos. This reveals the final problem: verifier rejects accesses to bpf_sysctl fields with offset > 0. Such accesses are already allowed for a wide range of structs: __sk_buff, bpf_sock_addr and sk_msg_md to name a few. Extend this support to bpf_sysctl by using bpf_ctx_range instead of offsetof when matching field offsets. Fixes: 7b146cebe30c ("bpf: Sysctl hook") Fixes: e1550bfe0de4 ("bpf: Add file_pos field to bpf_sysctl ctx") Fixes: 9a1027e52535 ("selftests/bpf: Test file_pos field in bpf_sysctl ctx") Signed-off-by: Ilya Leoshkevich --- kernel/bpf/cgroup.c | 4 ++-- tools/testing/selftests/bpf/test_sysctl.c | 8 +++++++- 2 files changed, 9 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index ddd8addcdb5c..a3eaf08e7dd3 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -1311,12 +1311,12 @@ static bool sysctl_is_valid_access(int off, int size, enum bpf_access_type type, return false; switch (off) { - case offsetof(struct bpf_sysctl, write): + case bpf_ctx_range(struct bpf_sysctl, write): if (type != BPF_READ) return false; bpf_ctx_record_field_size(info, size_default); return bpf_ctx_narrow_access_ok(off, size, size_default); - case offsetof(struct bpf_sysctl, file_pos): + case bpf_ctx_range(struct bpf_sysctl, file_pos): if (type == BPF_READ) { bpf_ctx_record_field_size(info, size_default); return bpf_ctx_narrow_access_ok(off, size, size_default); diff --git a/tools/testing/selftests/bpf/test_sysctl.c b/tools/testing/selftests/bpf/test_sysctl.c index a320e3844b17..7c6e5b173f33 100644 --- a/tools/testing/selftests/bpf/test_sysctl.c +++ b/tools/testing/selftests/bpf/test_sysctl.c @@ -161,9 +161,14 @@ static struct sysctl_test tests[] = { .descr = "ctx:file_pos sysctl:read read ok narrow", .insns = { /* If (file_pos == X) */ +#if __BYTE_ORDER == __LITTLE_ENDIAN BPF_LDX_MEM(BPF_B, BPF_REG_7, BPF_REG_1, offsetof(struct bpf_sysctl, file_pos)), - BPF_JMP_IMM(BPF_JNE, BPF_REG_7, 0, 2), +#else + BPF_LDX_MEM(BPF_B, BPF_REG_7, BPF_REG_1, + offsetof(struct bpf_sysctl, file_pos) + 3), +#endif + BPF_JMP_IMM(BPF_JNE, BPF_REG_7, 4, 2), /* return ALLOW; */ BPF_MOV64_IMM(BPF_REG_0, 1), @@ -176,6 +181,7 @@ static struct sysctl_test tests[] = { .attach_type = BPF_CGROUP_SYSCTL, .sysctl = "kernel/ostype", .open_flags = O_RDONLY, + .seek = 4, .result = SUCCESS, }, { -- 2.23.0