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 24455C433EF for ; Tue, 7 Jun 2022 20:28:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359473AbiFGUZA (ORCPT ); Tue, 7 Jun 2022 16:25:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355053AbiFGTcW (ORCPT ); Tue, 7 Jun 2022 15:32:22 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A1EFE113B78; Tue, 7 Jun 2022 11:12:54 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id C0C85B82182; Tue, 7 Jun 2022 18:12:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29E8AC385A2; Tue, 7 Jun 2022 18:12:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1654625571; bh=GqappdJ46XNiKfc/847FHFLyVCNgfObnyezwpSKixLM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y2jl+YxIT4p64kTCsGael6CLyK8JYuoUGnIsdvmpy60atvZ9eMJBpuJO1CiksadwE eU6T8ljSB11G3czBQ7+vlDgRM0yvPm6jnsVcB+4XSlnuOtCcJdTt1cXJXW42fg2Ibl F1JjJ+tknTMJZk3hHzDnefG2fZPhb8y33tRJsKbU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Runqing Yang , Andrii Nakryiko , Sasha Levin Subject: [PATCH 5.17 065/772] libbpf: Fix a bug with checking bpf_probe_read_kernel() support in old kernels Date: Tue, 7 Jun 2022 18:54:17 +0200 Message-Id: <20220607164950.955107013@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220607164948.980838585@linuxfoundation.org> References: <20220607164948.980838585@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Runqing Yang [ Upstream commit d252a4a499a07bec21c65873f605c3a1ef52ffed ] Background: Libbpf automatically replaces calls to BPF bpf_probe_read_{kernel,user} [_str]() helpers with bpf_probe_read[_str](), if libbpf detects that kernel doesn't support new APIs. Specifically, libbpf invokes the probe_kern_probe_read_kernel function to load a small eBPF program into the kernel in which bpf_probe_read_kernel API is invoked and lets the kernel checks whether the new API is valid. If the loading fails, libbpf considers the new API invalid and replaces it with the old API. static int probe_kern_probe_read_kernel(void) { struct bpf_insn insns[] = { BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), /* r1 = r10 (fp) */ BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8), /* r1 += -8 */ BPF_MOV64_IMM(BPF_REG_2, 8), /* r2 = 8 */ BPF_MOV64_IMM(BPF_REG_3, 0), /* r3 = 0 */ BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_probe_read_kernel), BPF_EXIT_INSN(), }; int fd, insn_cnt = ARRAY_SIZE(insns); fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL", insns, insn_cnt, NULL); return probe_fd(fd); } Bug: On older kernel versions [0], the kernel checks whether the version number provided in the bpf syscall, matches the LINUX_VERSION_CODE. If not matched, the bpf syscall fails. eBPF However, the probe_kern_probe_read_kernel code does not set the kernel version number provided to the bpf syscall, which causes the loading process alwasys fails for old versions. It means that libbpf will replace the new API with the old one even the kernel supports the new one. Solution: After a discussion in [1], the solution is using BPF_PROG_TYPE_TRACEPOINT program type instead of BPF_PROG_TYPE_KPROBE because kernel does not enfoce version check for tracepoint programs. I test the patch in old kernels (4.18 and 4.19) and it works well. [0] https://elixir.bootlin.com/linux/v4.19/source/kernel/bpf/syscall.c#L1360 [1] Closes: https://github.com/libbpf/libbpf/issues/473 Signed-off-by: Runqing Yang Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220409144928.27499-1-rainkin1993@gmail.com Signed-off-by: Sasha Levin --- tools/lib/bpf/libbpf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 94a6a8543cbc..41515a770e3a 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -4564,7 +4564,7 @@ static int probe_kern_probe_read_kernel(void) }; int fd, insn_cnt = ARRAY_SIZE(insns); - fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL", insns, insn_cnt, NULL); + fd = bpf_prog_load(BPF_PROG_TYPE_TRACEPOINT, NULL, "GPL", insns, insn_cnt, NULL); return probe_fd(fd); } -- 2.35.1