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=-7.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 0F113C433DF for ; Mon, 24 Aug 2020 16:43:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6D5320738 for ; Mon, 24 Aug 2020 16:43:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ZOiYUyUZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728406AbgHXQnQ (ORCPT ); Mon, 24 Aug 2020 12:43:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54730 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728648AbgHXQm4 (ORCPT ); Mon, 24 Aug 2020 12:42:56 -0400 Received: from mail-pl1-x641.google.com (mail-pl1-x641.google.com [IPv6:2607:f8b0:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 204CCC061573; Mon, 24 Aug 2020 09:42:56 -0700 (PDT) Received: by mail-pl1-x641.google.com with SMTP id t11so4500153plr.5; Mon, 24 Aug 2020 09:42:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=w41OmkoPspYNv6XjOAw8ahtDnY6c9BDmvOxAxpZTttk=; b=ZOiYUyUZBx+y2twZVDLNRNj7XcDKPZeSrlH1pKR2XVXQPyltnrUiF5XIL2Pi3UOJE0 QESR928QCAsMbVv7IvrTsNl9dzQkt7ttEVo22hbkdd8dUrifgdVOREvnTvtePmoSa168 LUMoDzFfey129AAzeHQzzhMcEFJEBuPwK0iIGyg5eV7eeKQsyzjJYoSHqPx+kktCO0WP gucacHnk+svFErQYZFyKb3ISKViLF8l6FlE982tB0lCYr6KbI36mn3lZKElTno2t7VnW 88Qp4uOlQ1ROHrTxVoECzjBJHSxrk7CtSabgsYgfuVEBBLi35E8V9OKPG1xS/gAt6i3x vcgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=w41OmkoPspYNv6XjOAw8ahtDnY6c9BDmvOxAxpZTttk=; b=XWjF0UWuEodlXjHNgp8i//apwu5KIYoieQSC4toxkMu09gFzWdCQnk3rS7/xvpeNtD st+6SV3Z1J2s+bRDB4RQQbJIHEb7VVgJ0VYZJuxeTpRHHmgBKfeqEkT1xU96ZGk6ccyv Dk3w1Ez/sKQjAoPebUPk3ekkwdbf3CiHE6iFUd4M88Dtxy2ywb4mURuPKPSYLRtLuBNC FPtjfd43LhwlLAdd07FHAmmdkevC7pom7i3JkTfxVFsecOj9SpGIxlAK5/pcnicV8FWy Jnra4iO/MrFRGiQqrzopEhPbqxhgXWx9axkA9dnAdkVXwmO1gWw2lQo35G9qwdQTzm59 bgJQ== X-Gm-Message-State: AOAM532xbyb0CjwGzPbVqBnXExJ6zXrEpBj5In+HIk6sk0oV9TD5yPAy UQgr2Blrw3iSF/zN7FltwEo= X-Google-Smtp-Source: ABdhPJxoYGplA4PD2xcotuP1hn0qFIYRCnXteeEmPRirh/XXpaV6W9tmtVZLocyIxdzG6AVoTaXu5g== X-Received: by 2002:a17:90a:850b:: with SMTP id l11mr142577pjn.15.1598287375409; Mon, 24 Aug 2020 09:42:55 -0700 (PDT) Received: from [10.67.51.206] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id 2sm72768pjg.32.2020.08.24.09.42.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Aug 2020 09:42:54 -0700 (PDT) Subject: Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction To: Will Deacon Cc: Greg KH , Will Deacon , linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org, Catalin Marinas , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Mark Rutland , Mark Brown , Kristina Martsenko , Sami Tolvanen , Andrew Jones , Ard Biesheuvel , Nick Desaulniers , Fangrui Song , open list , "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" References: <20200709195034.15185-1-f.fainelli@gmail.com> <20200720130411.GB494210@kroah.com> <9c29080e-8b3a-571c-3296-e0487fa473fa@gmail.com> <20200807131429.GB664450@kroah.com> <20200821160316.GE21517@willie-the-truck> <7480435b-355d-b9f7-3a42-b72a9c4b6f63@gmail.com> <20200824163208.GA25316@willie-the-truck> From: Florian Fainelli Message-ID: Date: Mon, 24 Aug 2020 09:42:53 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.1.1 MIME-Version: 1.0 In-Reply-To: <20200824163208.GA25316@willie-the-truck> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/24/2020 9:32 AM, Will Deacon wrote: > Hi Florian, > > On Fri, Aug 21, 2020 at 10:16:23AM -0700, Florian Fainelli wrote: >> On 8/21/20 9:03 AM, Will Deacon wrote: >>> On Fri, Aug 07, 2020 at 03:14:29PM +0200, Greg KH wrote: >>>> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote: >>>>> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19? >>>>> >>>>> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/ >>>>> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/ >>>>> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/ >>>> >>>> Nope, I was waiting for Will's "ack" for these. >>> >>> This patch doesn't even build for me (the 'sb' macro is not defined in 4.9), >>> and I really wonder why we bother backporting it at all. Nobody's ever shown >>> it to be a problem in practice, and it's clear that this is just being >>> submitted to tick a box rather than anything else (otherwise it would build, >>> right?). >> >> Doh, I completely missed submitting the patch this depended on that's >> why I did not notice the build failure locally, sorry about that, what a >> shame. >> >> Would not be the same "tick a box" argument be used against your >> original submission then? Sure, I have not been able to demonstrate in >> real life this was a problem, however the same can be said about a lot >> security related fixes. > > Sort of, although I wrote the original patch because it was dead easy to do > and saved having to think too much about the problem, whereas the complexity > of backporting largerly diminishes that imo. > >> What if it becomes exploitable in the future, would not it be nice to >> have it in a 6 year LTS kernel? > > Even if people are stuck on an old LTS, they should still be taking the > regular updates for it, and we would obviously need to backport the fix if > it turned out to be exploitable (and hey, we could even test it then!). > >>> So I'm not going to Ack any of them. As with a lot of this side-channel >>> stuff the cure is far worse than the disease. >> Assuming that my v3 does build correctly, which it will, would you be >> keen on changing your position? > > Note that I'm not trying to block this patch from going in, I'm just saying > that I'm not supportive of it. Perhaps somebody from Arm can review it if > they think it's worth the effort. How about I submit the actual full series (two patches) and we take the discussion from there? Thanks for responding! -- Florian