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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1691DC433EF for ; Sat, 22 Jan 2022 03:31:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232338AbiAVDbh (ORCPT ); Fri, 21 Jan 2022 22:31:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50348 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231519AbiAVDbg (ORCPT ); Fri, 21 Jan 2022 22:31:36 -0500 Received: from mail-pj1-x1044.google.com (mail-pj1-x1044.google.com [IPv6:2607:f8b0:4864:20::1044]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA34CC06173B for ; Fri, 21 Jan 2022 19:31:36 -0800 (PST) Received: by mail-pj1-x1044.google.com with SMTP id s61-20020a17090a69c300b001b4d0427ea2so14958251pjj.4 for ; Fri, 21 Jan 2022 19:31:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=5MHDu14fQSpZJz7j+Zy4IPZMZTay0OWmUvOWDxBw93A=; b=INKQo1YbvsJ0nUiqtkfzWKb8Vtrx3tcW5M0oMJk99lgsN/zaaP15TvAobfvdllaybJ OH0K9EBScLHP0LzJ8vVllteyICpk7IKtpoKaCdAtcFVoP6rVATpMLqGAdaMM6meB+nA+ fSuXb/5i8qH1uvt/FvSQX+4O8tAK4q/mUU2gAOvZnTa0PjvWoPiTJkB+SbdZ8qFviiHu CXF7KA6+pboxfnqBKYVO/+CsEbBshyJJs+YYoSHWTau5DsiXzzk9bsOrYbuRbY3z5KL7 9GNCLxff/BWgOHAjDbiy+MnYVhejglZxOhnSZA4EgfMi65FVA+dXJocvOS4fQYiNQ+mA fBlg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=5MHDu14fQSpZJz7j+Zy4IPZMZTay0OWmUvOWDxBw93A=; b=mAqWcuTjW+CEQfDLE7G22vJjg6PBSgRfesaXc0oUiZTdjzJvtFJymdAgBHuTfpbphI bXJDUl+qQucMOnFmL/bGZzWJ12kIfe2Fl5MA/z0nUpBt4ciq3YkEFCyhDGPT3LyKn7M/ bUje/KldrDqZEMPlg1ScDsy3s7EHmh2vCHQEdGOKKd+AW6aDKC4UjEjAVem0CadorTXK lhv1kQgDYAqHnQ5f9FadKOCcSgyFhnUMgWAFTWuFVcT4hYsXySjEcDjVJ2bZn/I4BxUY e0BFBFRfrETlJE6r5tz5PcOW2xB91I6JOPovSmvwnePT7IZgKmzWQ7gPv5Q6mrjFGsrh K/uw== X-Gm-Message-State: AOAM5336Ys77qDovGhnPAXWl2MLd2bXvaQvamIOLmRxpWfJPkMC1Gddb +PM55DOVZzuFv02luZcDib8= X-Google-Smtp-Source: ABdhPJzOC1oJASmXXkHRQiiIeRJmSfYlycRr4p49rgXdlGYXVTYICxrME2lwg70Waw7n768spFrwsQ== X-Received: by 2002:a17:902:854b:b0:14a:dd78:479e with SMTP id d11-20020a170902854b00b0014add78479emr6477535plo.86.1642822296011; Fri, 21 Jan 2022 19:31:36 -0800 (PST) Received: from localhost ([2405:201:6014:d064:1fb1:21a:3dae:742c]) by smtp.gmail.com with ESMTPSA id u30sm8691464pfg.199.2022.01.21.19.31.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Jan 2022 19:31:35 -0800 (PST) Date: Sat, 22 Jan 2022 09:01:33 +0530 From: Kumar Kartikeya Dwivedi To: Usama Arif Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii.nakryiko@gmail.com, fam.zheng@bytedance.com, cong.wang@bytedance.com, song@kernel.org Subject: Re: [RFC bpf-next 2/3] bpf: add support for module helpers in verifier Message-ID: <20220122033133.ph4wrxcorl5uvspy@thp> References: <20220121193956.198120-1-usama.arif@bytedance.com> <20220121193956.198120-3-usama.arif@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220121193956.198120-3-usama.arif@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Sat, Jan 22, 2022 at 01:09:55AM IST, Usama Arif wrote: > After the kernel module registers the helper, its BTF id > and func_proto are available during verification. During > verification, it is checked to see if insn->imm is available > in the list of module helper btf ids. If it is, > check_helper_call is called, otherwise check_kfunc_call. > The module helper function proto is obtained in check_helper_call > via get_mod_helper_proto function. > > Signed-off-by: Usama Arif > --- > kernel/bpf/verifier.c | 50 +++++++++++++++++++++++++++++++++---------- > 1 file changed, 39 insertions(+), 11 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 8c5a46d41f28..bf7605664b95 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -6532,19 +6532,39 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn > int insn_idx = *insn_idx_p; > bool changes_data; > int i, err, func_id; > + const struct btf_type *func; > + const char *func_name; > + struct btf *desc_btf; > > /* find function prototype */ > func_id = insn->imm; > - if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID) { > - verbose(env, "invalid func %s#%d\n", func_id_name(func_id), > - func_id); > - return -EINVAL; > - } > > if (env->ops->get_func_proto) > fn = env->ops->get_func_proto(func_id, env->prog); > - if (!fn) { > - verbose(env, "unknown func %s#%d\n", func_id_name(func_id), > + > + if (func_id >= __BPF_FUNC_MAX_ID) { > + desc_btf = find_kfunc_desc_btf(env, insn->imm, insn->off); I am not sure this is right, even if we reached this point. add_kfunc_call would not be called for a helper call, which means the kfunc_btf_tab will not be populated. I think this code is not reachable from your test, which is why you didn't see this. More below. > + if (IS_ERR(desc_btf)) > + return PTR_ERR(desc_btf); > + > + fn = get_mod_helper_proto(desc_btf, func_id); > + if (!fn) { > + func = btf_type_by_id(desc_btf, func_id); > + func_name = btf_name_by_offset(desc_btf, func->name_off); > + verbose(env, "unknown module helper func %s#%d\n", func_name, > + func_id); > + return -EACCES; > + } > + } else if (func_id >= 0) { > + if (env->ops->get_func_proto) > + fn = env->ops->get_func_proto(func_id, env->prog); > + if (!fn) { > + verbose(env, "unknown in-kernel helper func %s#%d\n", func_id_name(func_id), > + func_id); > + return -EINVAL; > + } > + } else { > + verbose(env, "invalid func %s#%d\n", func_id_name(func_id), > func_id); > return -EINVAL; > } > @@ -11351,6 +11371,7 @@ static int do_check(struct bpf_verifier_env *env) > int insn_cnt = env->prog->len; > bool do_print_state = false; > int prev_insn_idx = -1; > + struct btf *desc_btf; > > for (;;) { > struct bpf_insn *insn; > @@ -11579,10 +11600,17 @@ static int do_check(struct bpf_verifier_env *env) > } > if (insn->src_reg == BPF_PSEUDO_CALL) > err = check_func_call(env, insn, &env->insn_idx); > - else if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) > - err = check_kfunc_call(env, insn, &env->insn_idx); > - else > - err = check_helper_call(env, insn, &env->insn_idx); > + else { > + desc_btf = find_kfunc_desc_btf(env, insn->imm, insn->off); > + if (IS_ERR(desc_btf)) > + return PTR_ERR(desc_btf); > + I didn't get this part at all. At this point src_reg can be BPF_PSEUDO_KFUNC_CALL, or 0 (for helper call). If it is a helper call, then find_kfunc_desc_btf using insn->imm and insn->off would be a bug. > + if (insn->src_reg == BPF_K || Why are you comparing it to BPF_K? I think your patch is not going through your logic in check_helper_call at all. In your selftest, you declare it using __ksym. This means src_reg will be encoded as BPF_PSEUDO_KFUNC_CALL (2), this if condition will never be hit (because BPF_K is 0), and you will do check_kfunc_call for it. TLDR; I think it is being checked as a normal kfunc call by the verifier. What am I missing? > + get_mod_helper_proto(desc_btf, insn->imm)) > + err = check_helper_call(env, insn, &env->insn_idx); > + else > + err = check_kfunc_call(env, insn, &env->insn_idx); > + } > if (err) > return err; > } else if (opcode == BPF_JA) { > -- > 2.25.1 >