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 A16B9C433B4 for ; Fri, 23 Apr 2021 16:18:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 71921611ED for ; Fri, 23 Apr 2021 16:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229931AbhDWQT3 (ORCPT ); Fri, 23 Apr 2021 12:19:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229519AbhDWQT2 (ORCPT ); Fri, 23 Apr 2021 12:19:28 -0400 Received: from mail-lf1-x12d.google.com (mail-lf1-x12d.google.com [IPv6:2a00:1450:4864:20::12d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1A269C061574; Fri, 23 Apr 2021 09:18:52 -0700 (PDT) Received: by mail-lf1-x12d.google.com with SMTP id r128so51336110lff.4; Fri, 23 Apr 2021 09:18:52 -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=nfGb5ogijPuDmXHwl7Pp4S+pfB7oeOGlVBJbleVgWig=; b=k26jh6sJdWKIhUIfW+ZWjFKWD5WIcJJXyoi4EDs/YlZRtblNGNdsZZMuNe3lKzoqmq DGMzzC3v+09cnKgMvFzRYGFTyTJ6wHbqeSi4QBiXo3lTqd+7yusq3P3elSLghZ8Lsd1v SN///YDz3G5hkl9dyIQC7direx/ItDMN2pOexKf6RfNxWwfDgMYfWbRSs1wCmeQwLeFy dA30VbM+N39JQdgvYZhfAcBwna7mpSfslPGVxZPDk2ezGjVc1yxQRgDli5IFp6KFaVpW kJhuv/P5arpPad0UrBmZ+4MusAfHo01xMOC9bU6zWhmT/tKowv/D2IK9+qgkFGhPSZMn mmBw== 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=nfGb5ogijPuDmXHwl7Pp4S+pfB7oeOGlVBJbleVgWig=; b=B0EaChIf/b3K6UzAB8DWd4tqUsJJ8Pg7mQ0hquosP8He5r3v8WAtVBB0Yi2q50FyVK zj2AZsEp+oNWHm4urbdezIHwrsA0qcBk6rGToG+IFXr0RUyl/3zuxPRy3JXxZZKgEhFV 5XhIzSkuvDeyTxGdjG1FjZ/MVMP2D7lW4p05x0bZ2/zODO1dQZ5sITwhWXIWKMFeIg2m XJKmqtge2hWOR29aFmfs8Y1Ap3iTX1n/FyWGtzbUk4YRW77ocueDNpGxb2OBU6tgo1TD 0PgT9ZGrR7Ox9/IEai1DoCREJtcHabYuyjWIeanBmredhh3jhB50XLC3JlLjrvRdQ40p InDQ== X-Gm-Message-State: AOAM530d9oSQs/smhsl0mwDH+OmfzEzlVXlP5WmWB1UX7PiEnp4bfYZh hwU2lKHDwUCJdiWFPWmH+E7/i1dp/VN2oB7QZvI= X-Google-Smtp-Source: ABdhPJwOEyiRALe1ACS/53iWPwPZsA+xQW1OjN6+bpp359brRJa+Wb4/rksowVu5nwEf7C6H0oGhoYH66Itfl023NOo= X-Received: by 2002:ac2:491a:: with SMTP id n26mr3512100lfi.539.1619194730603; Fri, 23 Apr 2021 09:18:50 -0700 (PDT) MIME-Version: 1.0 References: <20210416202404.3443623-1-andrii@kernel.org> <20210416202404.3443623-11-andrii@kernel.org> In-Reply-To: From: Alexei Starovoitov Date: Fri, 23 Apr 2021 09:18:39 -0700 Message-ID: Subject: Re: [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking To: Andrii Nakryiko 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 9:09 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 ? > /* 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; > }