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=-15.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=no 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 8E4F8C433DB for ; Sun, 17 Jan 2021 17:26:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 480082250F for ; Sun, 17 Jan 2021 17:26:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729880AbhAQR00 (ORCPT ); Sun, 17 Jan 2021 12:26:26 -0500 Received: from linux.microsoft.com ([13.77.154.182]:39950 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729877AbhAQR0Y (ORCPT ); Sun, 17 Jan 2021 12:26:24 -0500 Received: from [192.168.254.32] (unknown [47.187.219.45]) by linux.microsoft.com (Postfix) with ESMTPSA id A8F0120B7192; Sun, 17 Jan 2021 09:25:42 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com A8F0120B7192 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1610904343; bh=dSxgyZILd6ePeQFGFSfItK/jBXk7vqxGoh5JR1/STnU=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=NaeBDi7O+56Gh0KonoBTBOjzfe3hfWYRl6mCpb1uojoZiibtZgwkuczXfumqIW1Xm qLblMkxvZUO1VO/QuGbp2KyGbuFyRon9vp3BruaNST8Hd5OpKIg1DLmuMYc+LN2Pre JQ1/PqvGORj1UhGIMXUax1j8+WP3nJY/6SRq7ObU= Subject: Re: Live patching on ARM64 To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, Mark Brown , Julien Thierry , jpoimboe@redhat.com, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210115123347.GB39776@C02TD0UTHF1T.local> From: "Madhavan T. Venkataraman" Message-ID: Date: Sun, 17 Jan 2021 11:25:41 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210115123347.GB39776@C02TD0UTHF1T.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 1/15/21 6:33 AM, Mark Rutland wrote: >> It looks like the most recent work in this area has been from the >> following folks: >> >> Mark Brown and Mark Rutland: >> Kernel changes to providing reliable stack traces. >> >> Julien Thierry: >> Providing ARM64 support in objtool. >> >> Torsten Duwe: >> Ftrace with regs. > > IIRC that's about right. I'm also trying to make arm64 patch-safe (more > on that below), and there's a long tail of work there for anyone > interested. > OK. >> I apologize if I have missed anyone else who is working on Live Patching >> for ARM64. Do let me know. >> >> Is there any work I can help with? Any areas that need investigation, any code >> that needs to be written, any work that needs to be reviewed, any testing that >> needs to done? You folks are probably super busy and would not mind an extra >> hand. > > One general thing that I believe we'll need to do is to rework code to > be patch-safe (which implies being noinstr-safe too). For example, we'll > need to rework the instruction patching code such that this cannot end > up patching itself (or anything that has instrumented it) in an unsafe > way. > OK. > Once we have objtool it should be possible to identify those cases > automatically. Currently I'm aware that we'll need to do something in at > least the following places: > > * The entry code -- I'm currently chipping away at this. > OK. > * The insn framework (which is used by some patching code), since the > bulk of it lives in arch/arm64/kernel/insn.c and isn't marked noinstr. > > We can probably shift the bulk of the aarch64_insn_gen_*() and > aarch64_get_*() helpers into a header as __always_inline functions, > which would allow them to be used in noinstr code. As those are > typically invoked with a number of constant arguments that the > compiler can fold, this /might/ work out as an optimization if the > compiler can elide the error paths. > > * The alternatives code, since we call instrumentable and patchable > functions between updating instructions and performing all the > necessary maintenance. There are a number of cases within > __apply_alternatives(), e.g. > > - test_bit() > - cpus_have_cap() > - pr_info_once() > - lm_alias() > - alt_cb, if the callback is not marked as noinstr, or if it calls > instrumentable code (e.g. from the insn framework). > - clean_dcache_range_nopatch(), as read_sanitised_ftr_reg() and > related code can be instrumented. > > This might need some underlying rework elsewhere (e.g. in the > cpufeature code, or atomics framework). > OK. > So on the kernel side, maybe a first step would be to try to headerize > the insn generation code as __always_inline, and see whether that looks > ok? With that out of the way it'd be a bit easier to rework patching > code depending on the insn framework. > OK. I have an understanding of some of the above already. I will come up to speed on the others. I will email you any questions I might have. > I'm not sure about the objtool side, so I'll leave that to Julien and co > to answer. > Thanks for the information. Madhavan