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=-17.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 E7A2AC433E3 for ; Sat, 22 Aug 2020 00:44:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C328521775 for ; Sat, 22 Aug 2020 00:44:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="KxL3pP6y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726688AbgHVAoC (ORCPT ); Fri, 21 Aug 2020 20:44:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726871AbgHVAoB (ORCPT ); Fri, 21 Aug 2020 20:44:01 -0400 Received: from mail-ej1-x641.google.com (mail-ej1-x641.google.com [IPv6:2a00:1450:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6F86C061755 for ; Fri, 21 Aug 2020 17:44:00 -0700 (PDT) Received: by mail-ej1-x641.google.com with SMTP id g19so4578021ejc.9 for ; Fri, 21 Aug 2020 17:44:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ZiWSg+hYBkj5lzGxjv3JQWa7cVF6R88j6OVrhK2uYBA=; b=KxL3pP6yAfeMPoV7fDm3WekUknERTlN3sAOsvzQLQkyjAPp1Ai0394nLI+3h8BstI4 cru5zfAnacjkVdbkWZKptmu3nH5JmOdHq/mZXKeEkjrRDTiAPESIhswWFmdGY3J3Wa0P UWl9N6os5BIvy5xbJnvxPZmeQbI3R7rd6k1q7pNY7Tn0FRXChLTOaTf9z26toa3XC+rX B+M6JjoDPmc77B3lGYxP5YOv95QMIWagwMZI0jCVHBVP4f4UgBhs3qNZKNUBKW6x5Du6 ETkB8bZ2VZcINjgFqM8Zrqv7t7K19MHiNn0g0GmZ4j+YXBirIjRiZ8Ob8CZkBUtAISYa /hCA== 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=ZiWSg+hYBkj5lzGxjv3JQWa7cVF6R88j6OVrhK2uYBA=; b=tPZT+gHVsd1uV26+C4E+u3rqbNYYwU3Yk/E/OSoQ7lOQZRxqOwVOsZ/wFhuCjYAri6 4AXRBFV5sOhebuPLqxmC0tvGdHMwJuFW56oSg+qAX+7wQ8x+oYdpC9OAGDB50+CFnLuT 7Lqrw2UupdnMTR19hJqG0mogtNQZ75KMP7KnFzhOIJR11woa+ROzvB+xsltHIH0kpvzX uQsJ6ZDiNFGmb0zMdsA5w6zjEQsEuxoKwYvJJgpIHFd2RRhJTwweYyUMYLd1aLhCyjZD OUmTyg1uhtF7bGANwoCQPfF6tST1K0lH0kKNIR+SyhHVnnRycVPNm/ZBV8JsdP4vg/yy mmIg== X-Gm-Message-State: AOAM5305tXY7yXBL5erBwxf4XHog0Gk/fs13viwKCqHf1dtkgGzpeqUr 3R+AxVbPSjKdMNWVt8v94pxseQvdz4MZvSVLiTIEEQ== X-Google-Smtp-Source: ABdhPJzATvG66iDiWsnk9V+x2N0xgxATTIy14bazridH8+hJaAYN1Kl5IRln8g1MlvHdvXBuspRm0Pdsx3RKb+HBTR8= X-Received: by 2002:a17:906:54d3:: with SMTP id c19mr5711543ejp.408.1598057038351; Fri, 21 Aug 2020 17:43:58 -0700 (PDT) MIME-Version: 1.0 References: <20200819224030.1615203-1-haoluo@google.com> <20200819224030.1615203-4-haoluo@google.com> In-Reply-To: From: Hao Luo Date: Fri, 21 Aug 2020 17:43:47 -0700 Message-ID: Subject: Re: [PATCH bpf-next v1 3/8] bpf: Introduce help function to validate ksym's type. To: Andrii Nakryiko Cc: Yonghong Song , Networking , bpf , open list , "open list:KERNEL SELFTEST FRAMEWORK" , Shuah Khan , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Song Liu , John Fastabend , KP Singh , Quentin Monnet , Steven Rostedt , Ingo Molnar , Andrey Ignatov , Jakub Sitnicki Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Aug 21, 2020 at 2:50 PM Andrii Nakryiko wrote: > > On Thu, Aug 20, 2020 at 10:22 AM Yonghong Song wrote: > > > > > > > > On 8/19/20 3:40 PM, Hao Luo wrote: > > > For a ksym to be safely dereferenced and accessed, its type defined in > > > bpf program should basically match its type defined in kernel. Implement > > > a help function for a quick matching, which is used by libbpf when > > > resolving the kernel btf_id of a ksym. > > > > > > Signed-off-by: Hao Luo > > > --- [...] > > > +/* > > > + * Match a ksym's type defined in bpf programs against its type encoded in > > > + * kernel btf. > > > + */ > > > +bool btf_ksym_type_match(const struct btf *ba, __u32 id_a, > > > + const struct btf *bb, __u32 id_b) > > > +{ > > [...] > > > > + } > > > + } > > > > I am wondering whether this is too strict and how this can co-work with > > CO-RE. Forcing users to write almost identical structure definition to > > the underlying kernel will not be user friendly and may not work cross > > kernel versions even if the field user cares have not changed. > > > > Maybe we can relax the constraint here. You can look at existing > > libbpf CO-RE code. > > Right. Hao, can you just re-use bpf_core_types_are_compat() instead? > See if semantics makes sense, but I think it should. BPF CO-RE has > been permissive in terms of struct size and few other type aspects, > because it handles relocations so well. This approach allows to not > have to exactly match all possible variations of some struct > definition, which is a big problem with ever-changing kernel data > structures. > I have to say I hate myself writing another type comparison instead of reusing the existing one. The issue is that when bpf_core_types_compat compares names, it uses t1->name_off == t2->name_off. It is also used in bpf_equal_common(). In my case, because these types are from two different BTFs, their name_off are not expected to be the same, right? I didn't find a good solution to refactor before posting this patch. I think I can adapt bpf_core_type_compat() and pay more attention to CO-RE. > > > > > + break; > > > + } > > [...] > > > > + > > > struct btf_ext_sec_setup_param { > > > __u32 off; > > > __u32 len; > > > diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h > > > index 91f0ad0e0325..5ef220e52485 100644 > > > --- a/tools/lib/bpf/btf.h > > > +++ b/tools/lib/bpf/btf.h > > > @@ -52,6 +52,8 @@ LIBBPF_API int btf__get_map_kv_tids(const struct btf *btf, const char *map_name, > > > __u32 expected_key_size, > > > __u32 expected_value_size, > > > __u32 *key_type_id, __u32 *value_type_id); > > > +LIBBPF_API bool btf_ksym_type_match(const struct btf *ba, __u32 id_a, > > > + const struct btf *bb, __u32 id_b); > > > > > > LIBBPF_API struct btf_ext *btf_ext__new(__u8 *data, __u32 size); > > > LIBBPF_API void btf_ext__free(struct btf_ext *btf_ext); > > > > The new API function should be added to libbpf.map. > > My question is why does this even have to be a public API? I can fix. Please pardon my ignorance, what is the difference between public and internal APIs? I wasn't sure, so used it improperly. Thanks, Hao