From patchwork Tue Sep 8 17:57:02 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yonghong Song X-Patchwork-Id: 1359878 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: incoming-bpf@patchwork.ozlabs.org Delivered-To: patchwork-incoming-bpf@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=bpf-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=reject dis=none) header.from=fb.com Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=fb.com header.i=@fb.com header.a=rsa-sha256 header.s=facebook header.b=Qux6/HX6; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4BmCXg49qwz9sTX for ; Wed, 9 Sep 2020 03:57:23 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732064AbgIHR5T (ORCPT ); Tue, 8 Sep 2020 13:57:19 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:45778 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729802AbgIHR5K (ORCPT ); Tue, 8 Sep 2020 13:57:10 -0400 Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 088HtdEW016449 for ; Tue, 8 Sep 2020 10:57:09 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding : content-type; s=facebook; bh=sX1lDjbtcr4lFFYhSncUWs+xJYEs/aYPfXw8eZepxVs=; b=Qux6/HX6X1AuBjD7LNpeKdFEXi4ELxXuKHfjGmqOOoAT9Ipao/3CSW1/J/lPhb28cT1+ uIB3dEG2rSS3leZNlR2RdvyU7yC8jHdFGJL8ETtqXjNAbW9ioEHNIzng/u0Cc+ocxvRe av0cpMpSjEFVXbfdT+JiGcq98nvvWwGbvLc= Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com with ESMTP id 33ctr6aqy1-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 08 Sep 2020 10:57:09 -0700 Received: from intmgw002.03.ash8.facebook.com (2620:10d:c085:108::8) by mail.thefacebook.com (2620:10d:c085:11d::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1979.3; Tue, 8 Sep 2020 10:57:08 -0700 Received: by devbig003.ftw2.facebook.com (Postfix, from userid 128203) id A91643704E21; Tue, 8 Sep 2020 10:57:02 -0700 (PDT) From: Yonghong Song To: , CC: Alexei Starovoitov , Daniel Borkmann , Subject: [PATCH bpf-next v3 1/2] bpf: permit map_ptr arithmetic with opcode add and offset 0 Date: Tue, 8 Sep 2020 10:57:02 -0700 Message-ID: <20200908175702.2463625-1-yhs@fb.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200908175702.2463416-1-yhs@fb.com> References: <20200908175702.2463416-1-yhs@fb.com> MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-09-08_09:2020-09-08,2020-09-08 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 mlxscore=0 mlxlogscore=999 phishscore=0 bulkscore=0 malwarescore=0 clxscore=1015 adultscore=0 suspectscore=8 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009080170 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Commit 41c48f3a98231 ("bpf: Support access to bpf map fields") added support to access map fields with CORE support. For example, struct bpf_map { __u32 max_entries; } __attribute__((preserve_access_index)); struct bpf_array { struct bpf_map map; __u32 elem_size; } __attribute__((preserve_access_index)); struct { __uint(type, BPF_MAP_TYPE_ARRAY); __uint(max_entries, 4); __type(key, __u32); __type(value, __u32); } m_array SEC(".maps"); SEC("cgroup_skb/egress") int cg_skb(void *ctx) { struct bpf_array *array = (struct bpf_array *)&m_array; /* .. array->map.max_entries .. */ } In kernel, bpf_htab has similar structure, struct bpf_htab { struct bpf_map map; ... } In the above cg_skb(), to access array->map.max_entries, with CORE, the clang will generate two builtin's. base = &m_array; /* access array.map */ map_addr = __builtin_preserve_struct_access_info(base, 0, 0); /* access array.map.max_entries */ max_entries_addr = __builtin_preserve_struct_access_info(map_addr, 0, 0); max_entries = *max_entries_addr; In the current llvm, if two builtin's are in the same function or in the same function after inlining, the compiler is smart enough to chain them together and generates like below: base = &m_array; max_entries = *(base + reloc_offset); /* reloc_offset = 0 in this case */ and we are fine. But if we force no inlining for one of functions in test_map_ptr() selftest, e.g., check_default(), the above two __builtin_preserve_* will be in two different functions. In this case, we will have code like: func check_hash(): reloc_offset_map = 0; base = &m_array; map_base = base + reloc_offset_map; check_default(map_base, ...) func check_default(map_base, ...): max_entries = *(map_base + reloc_offset_max_entries); In kernel, map_ptr (CONST_PTR_TO_MAP) does not allow any arithmetic. The above "map_base = base + reloc_offset_map" will trigger a verifier failure. ; VERIFY(check_default(&hash->map, map)); 0: (18) r7 = 0xffffb4fe8018a004 2: (b4) w1 = 110 3: (63) *(u32 *)(r7 +0) = r1 R1_w=invP110 R7_w=map_value(id=0,off=4,ks=4,vs=8,imm=0) R10=fp0 ; VERIFY_TYPE(BPF_MAP_TYPE_HASH, check_hash); 4: (18) r1 = 0xffffb4fe8018a000 6: (b4) w2 = 1 7: (63) *(u32 *)(r1 +0) = r2 R1_w=map_value(id=0,off=0,ks=4,vs=8,imm=0) R2_w=invP1 R7_w=map_value(id=0,off=4,ks=4,vs=8,imm=0) R10=fp0 8: (b7) r2 = 0 9: (18) r8 = 0xffff90bcb500c000 11: (18) r1 = 0xffff90bcb500c000 13: (0f) r1 += r2 R1 pointer arithmetic on map_ptr prohibited To fix the issue, let us permit map_ptr + 0 arithmetic which will result in exactly the same map_ptr. Signed-off-by: Yonghong Song Acked-by: Andrii Nakryiko --- kernel/bpf/verifier.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b4e9c56b8b32..814bc6c1ad16 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5317,6 +5317,10 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, dst, reg_type_str[ptr_reg->type]); return -EACCES; case CONST_PTR_TO_MAP: + /* smin_val represents the known value */ + if (known && smin_val == 0 && opcode == BPF_ADD) + break; + /* fall-through */ case PTR_TO_PACKET_END: case PTR_TO_SOCKET: case PTR_TO_SOCKET_OR_NULL: