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 2721A29A2 for ; Mon, 26 Aug 2024 09:49:21 +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=1724665762; cv=none; b=NcBJxmsNi79dayk3u12w5ehOAB0jQeCcDK4G9wf2497vjgem+0vHb8ryjWBd+9I6Twkd8YuCjOVquz5MbshipazYnRQWUnF8L80UylUx+oh6GxdgEAfFAAvfRj9AtiNRGE61ucvC4NCSWTWQ6xFOXPjEolOW0wyx0W5puCgXnp8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724665762; c=relaxed/simple; bh=UZ8wGyTtDZPkcuELuMqzkQnaOqqzcvh1xpGLIvO+5l4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HkmxHJ/mAcaNH9BJu4hLYwuW8wbzUHC5kUwO1ho+rLgrEZ4xC7p2FT1mUBvzG16J6y68mJdrv5odxP+yFCL010LPEhLaPdMIYz47W2UBX0hmAHIfhPRCDvd0cft2vwiM/HARYnzE4LJf7KmFjjjCRJu1YsW/B7K4GNtdAP7ELrg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NhK9vfK2; 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="NhK9vfK2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B2D4DC4FDFE; Mon, 26 Aug 2024 09:49:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724665761; bh=UZ8wGyTtDZPkcuELuMqzkQnaOqqzcvh1xpGLIvO+5l4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=NhK9vfK25OxxNzv31v6zZk1aOz6Lj6UuS45BmiaOGHVmqNyLn9p4HukCoclX/fY2s Y3OwH/AqgSvqGs1Yb3mOjsbU+4BYgJcGumg9urXR48j1plNdLb538fMIHwhfjAKnVb PIZ8BXHrZ5yNSm9dvyh14nq+QBlGL4STyq9GdYzqi8yMWvCnmI9Sb55vw9BvaMq+Zg 42ZxvpC6WNYTb500ADKJDB+yHNjWG5oQRQYGf/m7HOCcr12tPtBajh3BOiroraugD7 gHx0TzIy26hnpQ3wLUxXdJIA4BK1PvDi75M5aTN1O+VIjV7mCwzGsJgv80LKmaPg3H TX5GIMkOZK+RQ== Message-ID: <4787c89e-e273-41da-b7a4-d3d58d755b76@kernel.org> Date: Mon, 26 Aug 2024 11:49:18 +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> <547fdd31-a052-4274-a59e-d7177887dbbe@kernel.org> <010b2338434b7df67ac418ad7063543e91c946b9.camel@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, Martin, On 26/08/2024 11:24, Geliang Tang wrote: > Hi Matt, Martin, > > On Mon, 2024-08-26 at 10:44 +0200, Matthieu Baerts wrote: >> 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.) > > We must do the cast, otherwise, an "access beyond struct list_head" > occurs: > > ; token = subflow->token; @ mptcp_subflow.c:92 > 13: (61) r4 = *(u32 *)(r1 +524) > access beyond struct list_head at off 524 size 4 OK! > > See Martin's comment in [1]. > > [1] > https://patchwork.kernel.org/project/netdevbpf/patch/20240805-upstream-bpf-next-20240506-mptcp-subflow-test-v4-2-2b4ca6994993@kernel.org/ > >> >>>                 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. > > A read-only function will get the same error. > > I added a read-only function mptcp_subflow_get_scheduled() for testing: > > bool mptcp_subflow_get_scheduled(struct mptcp_subflow_context *subflow) Do you have the same issue if '*subflow' is marked as 'const'? > { > return subflow->scheduled; > } > > And invoke it from BPF in mptcp_for_each_subflow() loop: > > 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); > mptcp_subflow_get_scheduled(subflow); > } > return 0; > } > > The same "arg#0 is untrusted_ptr_ expected ptr_ or socket" occurs. > > Hope Martin can give us a solution for this issue. > > Thanks, > -Geliang > >> >> 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 > Cheers, Matt -- Sponsored by the NGI0 Core fund.