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 11755C433B4 for ; Fri, 23 Apr 2021 04:25:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC04B6120D for ; Fri, 23 Apr 2021 04:25:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229456AbhDWE0V (ORCPT ); Fri, 23 Apr 2021 00:26:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229454AbhDWE0U (ORCPT ); Fri, 23 Apr 2021 00:26:20 -0400 Received: from mail-yb1-xb36.google.com (mail-yb1-xb36.google.com [IPv6:2607:f8b0:4864:20::b36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D028DC061574; Thu, 22 Apr 2021 21:25:44 -0700 (PDT) Received: by mail-yb1-xb36.google.com with SMTP id z1so54128370ybf.6; Thu, 22 Apr 2021 21:25:44 -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=lXAkZ+YAfZxx+0potAZ3BS9XSrbIjZz3+t1gWmWYx8E=; b=ROY51KI4bd0cl+G7KqbfkP0iEZvpAPke82VK5GEY3SolBNThtD52USP8a8Lwh/kqfA CGPXTPQG+X1msmuf4iZgQt5Kkotm2MZ2wuiZA1dYEy+f5lxP8gI2OobnaHURBX8llHXm VdTfl9LWpqkiOzvURI7hYgZu/gnSfyGdb1dvHDSs+DnqVcCMHqUrzhpRsMh2zbHXc/aC 1Kq/CvxqduN2UA57XaUZ4w4R4S+P0xBGnthtRCc874/lSJyD6Ku57KGqWsraM1GRFIoa B6O+UR6Kc4qBmiUpm1l2E35cJIX3wUV9+dk7UqxlLyhs3aNgrGkNuRuA9dpIGAuL+bQI Dd2g== 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=lXAkZ+YAfZxx+0potAZ3BS9XSrbIjZz3+t1gWmWYx8E=; b=AgCL7ks6tO2+w+Z72R0XRdcbMbSc+8FLGz4pFd1Km3EqbrWVSXmmtBzjVYRfUrb9Xz qffZFGwBVSfTdVGiu6cmWe7aUzUxq6EaoKoYtTo0StaHiAx3BYYTZIBUxvfiHUbnSxXT qwozbAnWSIgASLebVkRlFDzo8eB9/cqXw73tTEdPHkiD9W6gF5Zyho9X6DcUnkHKl8do u9OLls8I58MRA6IdTmmdsK6RLLFMaGwxfVt380s6r/Th4xJax8cqDxPt1/exi9cn4xcj a4cb7mTJ/QFtwLFY7Zt2HtOu2ugtxRlQ4S2ceNKJfmw/GYonltSvsb9KlWUAJ4olEl9e SjaA== X-Gm-Message-State: AOAM531/mu8X95KEoihrz7KhRxIK9fDz7EEwbq+Fmgr/7C8R93MhkvAu f2PRklXbxeFxtNkFTChSzIHx1pJ+FRPSvg2zz48= X-Google-Smtp-Source: ABdhPJwzmYEOdTE5Nbpxjxl6GfbRVsn2LVnXoVrZeoFIRLKY09JqugoYkk6hCG17XUmVklbzCKs0tDxcw7vBrVQOqlc= X-Received: by 2002:a25:2a0a:: with SMTP id q10mr1767484ybq.403.1619151944053; Thu, 22 Apr 2021 21:25:44 -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: Thu, 22 Apr 2021 21:25:33 -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 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. > 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). > My reading that it will abort the whole linking process and > this linker bug will be reported back to us. > So it's good. Right, it will be propagated all the way up.