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=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 9E250C433E0 for ; Thu, 30 Jul 2020 22:45:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 871C72084D for ; Thu, 30 Jul 2020 22:45:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730458AbgG3Wpf (ORCPT ); Thu, 30 Jul 2020 18:45:35 -0400 Received: from www62.your-server.de ([213.133.104.62]:35206 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730416AbgG3Wpe (ORCPT ); Thu, 30 Jul 2020 18:45:34 -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 1k1HIo-0008Dp-IE; Fri, 31 Jul 2020 00:45:30 +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 1k1HIo-0003Zs-7C; Fri, 31 Jul 2020 00:45:30 +0200 Subject: Re: [PATCH bpf-next 1/1] arm64: bpf: Add BPF exception tables To: Jean-Philippe Brucker Cc: Qian Cai , 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> <20200730211453.GA79372@lophozonia> From: Daniel Borkmann Message-ID: <74433d9e-012d-a20f-129f-ce934e8090aa@iogearbox.net> Date: Fri, 31 Jul 2020 00:45:29 +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: <20200730211453.GA79372@lophozonia> Content-Type: text/plain; charset=utf-8; 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 11:14 PM, Jean-Philippe Brucker wrote: > On Thu, Jul 30, 2020 at 09:47:39PM +0200, Daniel Borkmann wrote: >> 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. > > Yes please squash it into the original patch, sorry for the mess Done, thanks!