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=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 95166C433E2 for ; Thu, 17 Sep 2020 09:00:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D15220770 for ; Thu, 17 Sep 2020 09:00:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600333250; bh=YUpRAK2hv+ZY1z1wbFM4JkS3zRWCKMAo84o8MPgEdMQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=T11loPz64UQjvf3CYpnwOYF6O2kOA3sBm9tDFZisaTfCw593wBlUUP8G5huWL8Mr7 MszRY6CbsP2f3bTSEvdvdLbzYTR5VgbGI4bX1Twfh/8LqaNLgmtzIB3sCj2Zi4nkFf qRnXY6iacqA46cKwYtGaiH/gp1OqIC4909XEmR+s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726411AbgIQJAr (ORCPT ); Thu, 17 Sep 2020 05:00:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:46148 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726211AbgIQJAr (ORCPT ); Thu, 17 Sep 2020 05:00:47 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C15D4206A2; Thu, 17 Sep 2020 09:00:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600333246; bh=YUpRAK2hv+ZY1z1wbFM4JkS3zRWCKMAo84o8MPgEdMQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bFHSbW5XHotn8JY5ZnNn9TTbo2v6ZKKSh9rAJoC2UJ7zPFR9YEc0twYS9BVjaxD2d 0Ss3X7SUKCXfsanrIt1RQCTKYkHv3eIDttPkH5CFIT8aju8WbiOAZ7oC11xn9lzm+d +4cYKUx/dtIFP1IJnAlq/Hv8zV6GSvWAITQvDPBE= Date: Thu, 17 Sep 2020 10:00:38 +0100 From: Will Deacon To: Ilias Apalodimas Cc: bpf@vger.kernel.org, ardb@kernel.org, naresh.kamboju@linaro.org, xi.wang@gmail.com, luke.r.nels@gmail.com, Jiri Olsa , Jean-Philippe Brucker , Yauheni Kaliuta , Daniel Borkmann , Alexei Starovoitov , Zi Shen Lim , Catalin Marinas , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , John Fastabend , KP Singh , "David S. Miller" , Jakub Kicinski , Jesper Dangaard Brouer , netdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] arm64: bpf: Fix branch offset in JIT Message-ID: <20200917090037.GA29556@willie-the-truck> References: <20200917084925.177348-1-ilias.apalodimas@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200917084925.177348-1-ilias.apalodimas@linaro.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 17, 2020 at 11:49:25AM +0300, Ilias Apalodimas wrote: > Running the eBPF test_verifier leads to random errors looking like this: > > [ 6525.735488] Unexpected kernel BRK exception at EL1 > [ 6525.735502] Internal error: ptrace BRK handler: f2000100 [#1] SMP > [ 6525.741609] Modules linked in: nls_utf8 cifs libdes libarc4 dns_resolver fscache binfmt_misc nls_ascii nls_cp437 vfat fat aes_ce_blk crypto_simd cryptd aes_ce_cipher ghash_ce gf128mul efi_pstore sha2_ce sha256_arm64 sha1_ce evdev efivars efivarfs ip_tables x_tables autofs4 btrfs blake2b_generic xor xor_neon zstd_compress raid6_pq libcrc32c crc32c_generic ahci xhci_pci libahci xhci_hcd igb libata i2c_algo_bit nvme realtek usbcore nvme_core scsi_mod t10_pi netsec mdio_devres of_mdio gpio_keys fixed_phy libphy gpio_mb86s7x > [ 6525.787760] CPU: 3 PID: 7881 Comm: test_verifier Tainted: G W 5.9.0-rc1+ #47 > [ 6525.796111] Hardware name: Socionext SynQuacer E-series DeveloperBox, BIOS build #1 Jun 6 2020 > [ 6525.804812] pstate: 20000005 (nzCv daif -PAN -UAO BTYPE=--) > [ 6525.810390] pc : bpf_prog_c3d01833289b6311_F+0xc8/0x9f4 > [ 6525.815613] lr : bpf_prog_d53bb52e3f4483f9_F+0x38/0xc8c > [ 6525.820832] sp : ffff8000130cbb80 > [ 6525.824141] x29: ffff8000130cbbb0 x28: 0000000000000000 > [ 6525.829451] x27: 000005ef6fcbf39b x26: 0000000000000000 > [ 6525.834759] x25: ffff8000130cbb80 x24: ffff800011dc7038 > [ 6525.840067] x23: ffff8000130cbd00 x22: ffff0008f624d080 > [ 6525.845375] x21: 0000000000000001 x20: ffff800011dc7000 > [ 6525.850682] x19: 0000000000000000 x18: 0000000000000000 > [ 6525.855990] x17: 0000000000000000 x16: 0000000000000000 > [ 6525.861298] x15: 0000000000000000 x14: 0000000000000000 > [ 6525.866606] x13: 0000000000000000 x12: 0000000000000000 > [ 6525.871913] x11: 0000000000000001 x10: ffff8000000a660c > [ 6525.877220] x9 : ffff800010951810 x8 : ffff8000130cbc38 > [ 6525.882528] x7 : 0000000000000000 x6 : 0000009864cfa881 > [ 6525.887836] x5 : 00ffffffffffffff x4 : 002880ba1a0b3e9f > [ 6525.893144] x3 : 0000000000000018 x2 : ffff8000000a4374 > [ 6525.898452] x1 : 000000000000000a x0 : 0000000000000009 > [ 6525.903760] Call trace: > [ 6525.906202] bpf_prog_c3d01833289b6311_F+0xc8/0x9f4 > [ 6525.911076] bpf_prog_d53bb52e3f4483f9_F+0x38/0xc8c > [ 6525.915957] bpf_dispatcher_xdp_func+0x14/0x20 > [ 6525.920398] bpf_test_run+0x70/0x1b0 > [ 6525.923969] bpf_prog_test_run_xdp+0xec/0x190 > [ 6525.928326] __do_sys_bpf+0xc88/0x1b28 > [ 6525.932072] __arm64_sys_bpf+0x24/0x30 > [ 6525.935820] el0_svc_common.constprop.0+0x70/0x168 > [ 6525.940607] do_el0_svc+0x28/0x88 > [ 6525.943920] el0_sync_handler+0x88/0x190 > [ 6525.947838] el0_sync+0x140/0x180 > [ 6525.951154] Code: d4202000 d4202000 d4202000 d4202000 (d4202000) > [ 6525.957249] ---[ end trace cecc3f93b14927e2 ]--- > > The reason is the offset[] creation and later usage, while building > the eBPF body. The code currently omits the first instruction, since > build_insn() will increase our ctx->idx before saving it. > That was fine up until bounded eBPF loops were introduced. After that > introduction, offset[0] must be the offset of the end of prologue which > is the start of the 1st insn while, offset[n] holds the > offset of the end of n-th insn. > > When "taken loop with back jump to 1st insn" test runs, it will > eventually call bpf2a64_offset(-1, 2, ctx). Since negative indexing is > permitted, the current outcome depends on the value stored in > ctx->offset[-1], which has nothing to do with our array. > If the value happens to be 0 the tests will work. If not this error > triggers. > > commit 7c2e988f400e ("bpf: fix x64 JIT code generation for jmp to 1st insn") > fixed an indentical bug on x86 when eBPF bounded loops were introduced. > > So let's fix it by creating the ctx->offset[] differently. Track the > beginning of instruction and account for the extra instruction while > calculating the arm instruction offsets. > > Fixes: 2589726d12a1 ("bpf: introduce bounded loops") > Reported-by: Naresh Kamboju > Reported-by: Jiri Olsa > Co-developed-by: Jean-Philippe Brucker > Signed-off-by: Jean-Philippe Brucker > Co-developed-by: Yauheni Kaliuta > Signed-off-by: Yauheni Kaliuta > Signed-off-by: Ilias Apalodimas Acked-by: Will Deacon Catalin -- do you want to take this as a fix? Will