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=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 6ECB1C43461 for ; Fri, 4 Sep 2020 20:31:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 292972087C for ; Fri, 4 Sep 2020 20:31:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="bXq1pMwa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727951AbgIDUbK (ORCPT ); Fri, 4 Sep 2020 16:31:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726791AbgIDUbI (ORCPT ); Fri, 4 Sep 2020 16:31:08 -0400 Received: from mail-yb1-xb44.google.com (mail-yb1-xb44.google.com [IPv6:2607:f8b0:4864:20::b44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01530C061244; Fri, 4 Sep 2020 13:31:07 -0700 (PDT) Received: by mail-yb1-xb44.google.com with SMTP id c17so5282185ybe.0; Fri, 04 Sep 2020 13:31:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=zTe3Mx2s33ZrVvXymlinvaXGi3RaFuG6B/IAiGNQ5rs=; b=bXq1pMwaRwQVggUO4Ptcv/YIYF+DOLFLGHEurYYZP8qlgil53eWi/z0vogf2RcYCZC Ro6ThynCuvncXKHb1mTaL8eSscapbHD+mjhwFZ+rJBXaxPDZll/KYQeId9BqKWwM6nkJ RZBa4G9ZcgezwEq9fX5whvvESKtaQP7t3woLBYXIB6zw+ROCjMLqKpL/Bf4Kr0c3e+IJ 1z2Ki/Hcmm8j0n670X+kKR+06K/N5NF50tTMgVy+9zzQatGb8WKwBfpOJ0MLh/FaHe4E MCd/zIX4wYUodoCxGf8F9ldDUbp3F0IzA1CfGac/0gRQLnTNqWTOKKjOoXTW8VgLcMVQ KM3Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=zTe3Mx2s33ZrVvXymlinvaXGi3RaFuG6B/IAiGNQ5rs=; b=PHkwwjwyUaZ9/ujFNT8A4cAZhtPPNVAmArw3jF5TNFpqsZQW9PxauMqaykL0NO3t7t wXPXuzHXXI6MozuLMe/I5uZo4DzyV+P0WWdnl4EAn6oqzfgckQguf0OafoMdfrJCVxO/ qDsbzeorQyHxmVUAuRjHaNFDrtbnGG8legFnIKLRd/R0vCVmBbUOYBBQz6/24auTmBV6 X07ujARu0MRmIAHVqm2ej1JBmqLNcuwwP2iTKdHsrnbdw13NvOvLhuZvMHzOegCHPwvH 6x3nyx4YwmJwy7ksi0NEMv8JqSvH0qSbGXm7VZQW8e/eGUPrBpvbn+xGuqlqVukWsYZg 0KSA== X-Gm-Message-State: AOAM531cxBmWHgWsDbPdFxcx3jlcRcSHslmVoceLuIcJGmsK9b1H5Zrl wInVyXcn1BtV3X9aLASaprtir8kxvrOEyxNGueI= X-Google-Smtp-Source: ABdhPJwNV/A0GEf144SXS3gF1pclDXRgHiyZ0LP/quE5bcqB/zFmX5pQ9eJfnmWYUWx+1P6jj9M+jRzIkiGakYBAqOQ= X-Received: by 2002:a25:ad5a:: with SMTP id l26mr11862621ybe.510.1599251466796; Fri, 04 Sep 2020 13:31:06 -0700 (PDT) MIME-Version: 1.0 References: <20200904194900.3031319-1-yhs@fb.com> <20200904194900.3031377-1-yhs@fb.com> In-Reply-To: <20200904194900.3031377-1-yhs@fb.com> From: Andrii Nakryiko Date: Fri, 4 Sep 2020 13:30:55 -0700 Message-ID: Subject: Re: [PATCH bpf-next 1/2] bpf: permit map_ptr arithmetic with opcode add and offset 0 To: Yonghong Song Cc: bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Sep 4, 2020 at 12:49 PM Yonghong Song wrote: > > 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 > --- > kernel/bpf/verifier.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index b4e9c56b8b32..92aa985e99df 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -5317,6 +5317,9 @@ 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: > + if (known && smin_val == 0 && opcode == BPF_ADD) does smin_val imply that var_off is strictly zero? if that's the case, can you please leave a comment stating this clearly, it's hard to tell if that's enough of a check. > + break; > + /* fall-through */ > case PTR_TO_PACKET_END: > case PTR_TO_SOCKET: > case PTR_TO_SOCKET_OR_NULL: > -- > 2.24.1 >