From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4D1AC13B59E for ; Mon, 26 Aug 2024 08:44:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724661877; cv=none; b=bpREV3SHUqIig53l4b8Ks6vzQa1HHpbT2ura5pm9lnZtQ3hdn9OJf3qgr8gTtlfW3rUS4KLx7/qe84cNqpmaqi7XgcJpsgrRiy9piNBVm32BmlL56vr8uGX1c738HrULROsqigS7QXUVafEQAh0a5YxsP52GsC4+Zn2hK/NCTLM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724661877; c=relaxed/simple; bh=4IdDiSTDfdWjDVsdlyV32q2YiCZWaFF03eVWQZDf4T4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EBXjKV6Gmdfd/odIol8ymLkpIwdVyr/ps4JTBEnAHF3UfrooQHrE00NGwZTxnmb8J7e+7vvNPmq3O6YYmKRunnhEgAWQ7kTMv3daa4FichSJ89F1scEdDZeuh22TxI3tGkUUgS8046L8Rz1JTvwRsUNtYXeL9mhorVp7qg+O1yI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DR67tMGc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DR67tMGc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD7E7C91B7D; Mon, 26 Aug 2024 08:44:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724661876; bh=4IdDiSTDfdWjDVsdlyV32q2YiCZWaFF03eVWQZDf4T4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=DR67tMGciQjhqHYr7sNd3KLuMN6t7cG+d0NrjsVAlRYUawLFnp54blyZJmKMReQck 2akUtN4BT92mf6iJ5wWosGY45eh1gp6nSV2Wv8pMTrJZmx0KXGxDz9xdyI08jUo4vG 2KN6MOAsummjQE+MzG8XFOgiQwmMqdxHwWKlYC0CmZz/9SAUD3qAWpsId6nOHgJRm1 9HQ3fMAMaKK0QdgDL+sgSKyFW6O2t3CskgdZg4OiNtE455TNGnp8s/ZjVgsgnx9dNr 5mDm98iV1C9DbGvc7l7R9SgUa5VAD8xtJxuWDM7ZSDueznobLul2jomjnPkarb/Lx3 X16gk7cDhu2og== Message-ID: <547fdd31-a052-4274-a59e-d7177887dbbe@kernel.org> Date: Mon, 26 Aug 2024 10:44:33 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-next 2/2] selftests/bpf: Add getsockopt to inspect mptcp subflow Content-Language: en-GB To: Geliang Tang , Martin KaFai Lau Cc: Geliang Tang , mptcp@lists.linux.dev References: <3788544d841aa372a810f2d3dce905612063e872.1724142917.git.tanggeliang@kylinos.cn> <407f6a6a-344e-4f12-9293-e43b9a97f8d4@kernel.org> <23cffc2904df37874f35f106975fccc962d6cb8e.camel@kernel.org> <689e3694-d8f9-4511-8363-6f83a3bb1a1d@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Geliang, On 26/08/2024 04:57, Geliang Tang wrote: > On Wed, 2024-08-21 at 11:37 +0200, Matthieu Baerts wrote: >> On 21/08/2024 10:00, Geliang Tang wrote: >>> On Tue, 2024-08-20 at 11:48 +0200, Matthieu Baerts wrote: >>>> On 20/08/2024 10:44, Geliang Tang wrote: (...) >>>>> + mptcp_for_each_subflow(msk, subflow) { >>>> >>>> (might be better to use this helper in our WIP MPTCP BPF packets >>>> scheduler examples, instead of converting them to a fixed array) >>> >>> Yes, but there are still some access permission issues that need to >>> be >>> resolved. >> >> OK, because structures cannot be modified I suppose. > > No, it seems the subflow cast by bpf_core_cast() can't be passed to a > kernel function, regardless of whether this function modifies the > subflow or not. An "arg#0 is untrusted_ptr_ expected ptr_" error > occurs. > > For example, mptcp_subflow_active() is a kernel function, and pass the > subflow to it in progs/mptcp_bpf_first.c like this: > > ''' > ... ... > extern bool mptcp_subflow_active(struct mptcp_subflow_context *subflow) > __ksym; > > ... ... > SEC("struct_ops") > int BPF_PROG(bpf_first_get_subflow, struct mptcp_sock *msk, > struct mptcp_sched_data *data) > { > struct mptcp_subflow_context *subflow, *tmp; > > mptcp_for_each_subflow(msk, tmp) { > subflow = bpf_core_cast(tmp, struct > mptcp_subflow_context); (Why do you need to cast "tmp" (struct mptcp_subflow_context *) in the same type of pointer? I don't think it changes anything for the error you got (see below), but it looks strange.) > if (!mptcp_subflow_active(subflow)) > continue; > } > return 0; > } > > ''' > > An "arg#0 is untrusted_ptr_ expected ptr_" error occurs: > > ''' > ; mptcp_for_each_subflow(msk, tmp) { @ mptcp_bpf_first.c:27 > 21: (e5) may_goto pc+1 > 22: R1=2488 R2=2488 R6=trusted_ptr_mptcp_sock(off=2488) R7=0 > R8=trusted_ptr_mptcp_sock(off=2488) R9=0 R10=fp0 > ; mptcp_for_each_subflow(msk, tmp) { @ mptcp_bpf_first.c:27 > 22: (05) goto pc-14 > 9: (79) r6 = *(u64 *)(r6 +0) ; R6_w=ptr_list_head() > 10: (1f) r6 -= r7 ; R6_w=ptr_list_head() R7=0 > 11: (bf) r1 = r6 ; R1_w=ptr_list_head() > R6_w=ptr_list_head() > 12: (0f) r1 += r7 ; R1=ptr_list_head() R7=0 > 13: (1d) if r1 == r8 goto pc+9 ; R1=ptr_list_head() > R8=trusted_ptr_mptcp_sock(off=2488) > ; subflow = bpf_core_cast(tmp, struct mptcp_subflow_context); @ > mptcp_bpf_first.c:28 > 14: (bf) r1 = r6 ; R1_w=ptr_list_head() > R6=ptr_list_head() > 15: (18) r2 = 0x6d14 ; R2_w=27924 > 17: (85) call bpf_rdonly_cast#159867 ; > R0_w=untrusted_ptr_mptcp_subflow_context() > ; if (!mptcp_subflow_active(subflow)) @ mptcp_bpf_first.c:29 > 18: (bf) r1 = r0 ; > R0_w=untrusted_ptr_mptcp_subflow_context() > R1_w=untrusted_ptr_mptcp_subflow_context() > 19: (85) call mptcp_subflow_active#111397 > arg#0 is untrusted_ptr_ expected ptr_ or socket > processed 23 insns (limit 1000000) max_states_per_insn 0 total_states 2 > peak_states 2 mark_read 2 > -- END PROG LOAD LOG -- > ''' > > How can I fix this? I need your advice. I'm not an expert in this, but I guess it means you cannot use 'mptcp_subflow_active()', because it can modify the 'subflow' structure that you got with bpf_core_cast() for a read-only usage. I guess it means we cannot iterate through the list and modify items from the list "directly" with BPF. Except if there is something else we can use, and I don't know about (which is very likely), we might have to continue extracting the subflows into an array of a fixed size. Cheers, Matt -- Sponsored by the NGI0 Core fund.