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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 87CDAC433B4 for ; Fri, 23 Apr 2021 16:31:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5238261445 for ; Fri, 23 Apr 2021 16:31:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231312AbhDWQbl (ORCPT ); Fri, 23 Apr 2021 12:31:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41186 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229549AbhDWQbl (ORCPT ); Fri, 23 Apr 2021 12:31:41 -0400 Received: from mail-yb1-xb2a.google.com (mail-yb1-xb2a.google.com [IPv6:2607:f8b0:4864:20::b2a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DBF25C061574; Fri, 23 Apr 2021 09:31:04 -0700 (PDT) Received: by mail-yb1-xb2a.google.com with SMTP id 82so56312555yby.7; Fri, 23 Apr 2021 09:31:04 -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=OgrthcEtekllzUoIdanX94ftCwR+7KLBAecNGPW6Ieo=; b=ut788sapQ6VgOIcNhwX37wW1uxJ7kIEzO4V3T06HkoHpa88vLRipZZDxYnUinUPLOt 2lsrGFDodu+pf+JS6Z5MKfokq2z6AhpezY5R6ji6KzvPOEuTBWi5icGAoALdvJiEjNaG 3tTNq8tecDT2dMEjhocgbiOmgrjCfmG09unI1P0zYoTrU8M/lOeeGvvgBB7/eY5cBA9C hDrv8hFK5D6OWwW6QLAzloSJ+cyiIenn3GM9GcCkvOXx1NPrg7+pWuxmYirFLCk0w1/6 LdW1yya2wObONKTrh5JQv6Lqrndz54JsX6hS0qn0ApCL8Mi9HXIHIORj3fPiAoT37mN4 BRpw== 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=OgrthcEtekllzUoIdanX94ftCwR+7KLBAecNGPW6Ieo=; b=Ykfjny48z6uQy32j0PuXXlrhUqYeJqQy/G5U13KRlrNx01/22wQwboRSQf0ZBN8tcl SYOvC5J2hQm1Q88V3Mlfuw6jLN6d4JzfXg0qY97tXyOyzpSOnL/Iu0BFPp7bUhTGalhb aHRMx8AQ3tvV0J9LzNXV+3XFA48AFrEW/1R4CPfDyQp+GNP42+iV6zvELdXcW2hKGOPE zDZ0ZAGZtxbZtxVitcr6TgUav9U6wOaAoaWFYUg7EcOeY/cchlEkMq4f+YAp4OZW57Bb JjHljfpEt06sV8F8aM9DndYsMglmaV0N7eFMXjGKgm2AgSwuko3P/CqDaZ6EZynf0utR 1Vjg== X-Gm-Message-State: AOAM5302s8dv/jM4RXOeIKPfhZ56+T7jrKuqWK6Ia96WjzJQ6PXtlShd t+ftDUf67TztGpIJBIUZrboQDmc8ryO+ssRV5MU= X-Google-Smtp-Source: ABdhPJzXGgzHlpjGlRdmvRSAL0QEisKhqG+ZHwUPaIrt76q3acRlKn/tkNmdTSISUdFKsoZKDm1pOB9vmvVWMgiy5M4= X-Received: by 2002:a25:3357:: with SMTP id z84mr6481666ybz.260.1619195464100; Fri, 23 Apr 2021 09:31:04 -0700 (PDT) MIME-Version: 1.0 References: <20210416202404.3443623-1-andrii@kernel.org> <20210416202404.3443623-11-andrii@kernel.org> In-Reply-To: From: Andrii Nakryiko Date: Fri, 23 Apr 2021 09:30:52 -0700 Message-ID: Subject: Re: [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking To: Alexei Starovoitov Cc: Yonghong Song , Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Apr 23, 2021 at 9:18 AM Alexei Starovoitov wrote: > > On Fri, Apr 23, 2021 at 9:09 AM Andrii Nakryiko > wrote: > > > > On Thu, Apr 22, 2021 at 10:11 PM Alexei Starovoitov > > wrote: > > > > > > On Thu, Apr 22, 2021 at 9:25 PM Andrii Nakryiko > > > wrote: > > > > > > > > On Thu, Apr 22, 2021 at 7:54 PM Alexei Starovoitov > > > > wrote: > > > > > > > > > > On Thu, Apr 22, 2021 at 11:24 AM Andrii Nakryiko > > > > > wrote: > > > > > > > > > > > > On Thu, Apr 22, 2021 at 9:50 AM Yonghong Song wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 4/16/21 1:23 PM, Andrii Nakryiko wrote: > > > > > > > > It should never fail, but if it does, it's better to know about this rather > > > > > > > > than end up with nonsensical type IDs. > > > > > > > > > > > > > > So this is defensive programming. Maybe do another round of > > > > > > > audit of the callers and if you didn't find any issue, you > > > > > > > do not need to check not-happening condition here? > > > > > > > > > > > > It's far from obvious that this will never happen, because we do a > > > > > > decently complicated BTF processing (we skip some types altogether > > > > > > believing that they are not used, for example) and it will only get > > > > > > more complicated with time. Just as there are "verifier bug" checks in > > > > > > kernel, this prevents things from going wild if non-trivial bugs will > > > > > > inevitably happen. > > > > > > > > > > I agree with Yonghong. This doesn't look right. > > > > > > > > I read it as Yonghong was asking about the entire patch. You seem to > > > > be concerned with one particular check, right? > > > > > > > > > The callback will be called for all non-void types, right? > > > > > so *type_id == 0 shouldn't never happen. > > > > > If it does there is a bug somewhere that should be investigated > > > > > instead of ignored. > > > > > > > > See btf_type_visit_type_ids() and btf_ext_visit_type_ids(), they call > > > > callback for every field that contains type ID, even if it points to > > > > VOID. So this can happen and is expected. > > > > > > I see. So something like 'extern cosnt void foo __ksym' would > > > point to void type? > > > But then why is it not a part of the id_map[] and has > > > to be handled explicitly? > > > > const void foo will be VAR -> CONST -> VOID. But any `void *` anywhere > > will be PTR -> VOID. Any void bla(int x) would have return type VOID > > (0), and so on. There are a lot of cases when we use VOID as type_id. > > VOID always is handled specially, because it stays zero despite any > > transformation: during BTF concatenation, BTF dedup, BTF generation, > > etc. > > > > > > > > > > The > > > > > if (new_id == 0) pr_warn > > > > > bit makes sense. > > > > > > > > Right, and this is the point of this patch. id_map[] will have zeroes > > > > for any unmapped type, so I just need to make sure I'm not false > > > > erroring on id_map[0] (== 0, which is valid, but never used). > > > > > > Right, id_map[0] should be 0. > > > I'm still missing something in this combination of 'if's. > > > May be do it as: > > > if (new_id == 0 && *type_id != 0) { pr_warn > > > ? > > > That was the idea? > > > > That's the idea, there is just no need to do VOID -> VOID > > transformation, but I'll rewrite it to a combined if if it makes it > > easier to follow. Here's full source of remap_type_id with few > > comments to added: > > > > static int remap_type_id(__u32 *type_id, void *ctx) > > { > > int *id_map = ctx; > > int new_id = id_map[*type_id]; > > > > > > /* Here VOID stays VOID, that's all */ > > > > if (*type_id == 0) > > return 0; > > Does it mean that id_map[0] is a garbage value? > and all other code that might be doing id_map[idx] might be reading > garbage if it doesn't have a check for idx == 0 ? No, id_map[0] == 0 by construction (id_map is obj->btf_type_map and is calloc()'ed) and can be used as id_map[idx]. > > > /* This means whatever type we are trying to remap didn't get a new ID > > assigned in linker->btf and that's an error */ > > if (new_id == 0) { > > pr_warn("failed to find new ID mapping for original > > BTF type ID %u\n", *type_id); > > return -EINVAL; > > } > > > > *type_id = id_map[*type_id]; > > > > return 0; > > }