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=-14.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 C6DD2C433DF for ; Thu, 30 Jul 2020 19:47:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A08CA20838 for ; Thu, 30 Jul 2020 19:47:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728636AbgG3Tro (ORCPT ); Thu, 30 Jul 2020 15:47:44 -0400 Received: from www62.your-server.de ([213.133.104.62]:36664 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726857AbgG3Tro (ORCPT ); Thu, 30 Jul 2020 15:47:44 -0400 Received: from sslproxy03.your-server.de ([88.198.220.132]) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1k1EWi-0007ew-B5; Thu, 30 Jul 2020 21:47:40 +0200 Received: from [178.196.57.75] (helo=pc-9.home) by sslproxy03.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1k1EWi-000C0T-0x; Thu, 30 Jul 2020 21:47:40 +0200 Subject: Re: [PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables To: Jean-Philippe Brucker , Qian Cai Cc: linux-arm-kernel@lists.infradead.org, bpf@vger.kernel.org, songliubraving@fb.com, andriin@fb.com, catalin.marinas@arm.com, john.fastabend@gmail.com, ast@kernel.org, zlim.lnx@gmail.com, kpsingh@chromium.org, yhs@fb.com, will@kernel.org, kafai@fb.com, sfr@canb.auug.org.au, linux-next@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200728152122.1292756-1-jean-philippe@linaro.org> <20200728152122.1292756-2-jean-philippe@linaro.org> <20200730122855.GA3773@lca.pw> <20200730142213.GB1529030@myrica> From: Daniel Borkmann Message-ID: Date: Thu, 30 Jul 2020 21:47:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20200730142213.GB1529030@myrica> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.3/25889/Thu Jul 30 17:03:53 2020) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 7/30/20 4:22 PM, Jean-Philippe Brucker wrote: > On Thu, Jul 30, 2020 at 08:28:56AM -0400, Qian Cai wrote: >> On Tue, Jul 28, 2020 at 05:21:26PM +0200, Jean-Philippe Brucker wrote: >>> When a tracing BPF program attempts to read memory without using the >>> bpf_probe_read() helper, the verifier marks the load instruction with >>> the BPF_PROBE_MEM flag. Since the arm64 JIT does not currently recognize >>> this flag it falls back to the interpreter. >>> >>> Add support for BPF_PROBE_MEM, by appending an exception table to the >>> BPF program. If the load instruction causes a data abort, the fixup >>> infrastructure finds the exception table and fixes up the fault, by >>> clearing the destination register and jumping over the faulting >>> instruction. >>> >>> To keep the compact exception table entry format, inspect the pc in >>> fixup_exception(). A more generic solution would add a "handler" field >>> to the table entry, like on x86 and s390. >>> >>> Signed-off-by: Jean-Philippe Brucker >> >> This will fail to compile on arm64, >> >> https://gitlab.com/cailca/linux-mm/-/blob/master/arm64.config >> >> arch/arm64/mm/extable.o: In function `fixup_exception': >> arch/arm64/mm/extable.c:19: undefined reference to `arm64_bpf_fixup_exception' > > Thanks for the report, I attached a fix. Daniel, can I squash it and > resend as v2 or is it too late? If you want I can squash your attached snippet into the original patch of yours. If you want to send a v2 that is fine as well of course. Let me know. Thanks, Daniel