Received: by 2002:a05:6a10:8c0a:0:0:0:0 with SMTP id go10csp773829pxb; Wed, 20 Jan 2021 22:08:15 -0800 (PST) X-Google-Smtp-Source: ABdhPJz2CHgit8Xjdyw/TdwsCmie87g7Pw+KgDAszgIAIO/AHNmKbJUnjYF2Gx3wzLeNlCgRal8y X-Received: by 2002:a05:6402:3186:: with SMTP id di6mr7113897edb.45.1611209294836; Wed, 20 Jan 2021 22:08:14 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1611209294; cv=none; d=google.com; s=arc-20160816; b=j0Ty0MUJp2NW6q7L+9lKLIrJMIxUPmQqtBknPLeAbznONXAPYntT7Nydp8WOVjmSP/ tvZPkSoB/hT9Wzi1W68LCbr4KlRG2yRRwXSrY2c+bj3XNt1c238L7Y04QEhwPyiHb2j0 KK7hSx1FkofxjG6+QS0sbTDamCyiHsUi1tFB1kawVCQpAoR8flhyypSAGlGSHjVIeqnB vEMj/UpqEjZ5NmVsrGmFm7f1Ty66x5SVm5KEfr41Jd2aWxCb0W0dLMmANMz63vhN3RjT 5OFp+p5LGKbUCANlyDjm5HKAN2pWdfb6MrPthlgHGyfImsifW8WIcmkr/ce4MlcUZrZ9 5p/A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:user-agent:message-id:references:in-reply-to :subject:cc:to:from:date:content-transfer-encoding:mime-version :sender:dkim-signature; bh=vMMS0y9cspIupZ5HdJuclFp1qJwYkuG3sETR3tQ2Syg=; b=OgppK/7Z+q5ZIkZZjeHInr9Y1GNA3xbKtcTR4rUzty1W6YjDWdJF1EdaYZ06FEUpr6 yRznXwsAa+pv8OBNBNNnMFzQHw4XFMFlXVF/lEHs3A5OP0p8wPetI8+du6eE9oM34HNV rfsEG8xMtELvoNA7bLpXB3lvc0oKVw96rYJEWEb/ARCaio8VK74ufwZSztc++H+hbi+s lTD+kLly7uThnvejfZBM5yYPn69hxY/kxWQ6WgDwViMa4x+dt8M8Ff4bOkxYi9XObSYu RC+EC/rfJ67OxSQBwOwSaDdW4k9jfQtUP39SJAtmME0OB6unP8poYu5nuBXMhzgclXjQ vZ9w== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@mg.codeaurora.org header.s=smtp header.b=MJ7LiTpv; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id v24si1741385eds.230.2021.01.20.22.07.50; Wed, 20 Jan 2021 22:08:14 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@mg.codeaurora.org header.s=smtp header.b=MJ7LiTpv; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726363AbhAUGFM (ORCPT + 99 others); Thu, 21 Jan 2021 01:05:12 -0500 Received: from a1.mail.mailgun.net ([198.61.254.60]:61813 "EHLO a1.mail.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726513AbhAUGEa (ORCPT ); Thu, 21 Jan 2021 01:04:30 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1611209032; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=vMMS0y9cspIupZ5HdJuclFp1qJwYkuG3sETR3tQ2Syg=; b=MJ7LiTpv0xap6xaU1VQ4Xk5sKH1T9LYbhC19//GTGLiZBotBXRIucUt/H9Wce/7eVdCFlljf SGUoDxphMwS1i0v3ztA+bjBHmrOR24zFvnOBNruVBOB6iZhIN5oemt+pwH6mqIxIiJyY8cU+ WijihSVChgMdLdRbVCMXRuO/Rsg= X-Mailgun-Sending-Ip: 198.61.254.60 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n01.prod.us-east-1.postgun.com with SMTP id 6009192ad75e1218e33a4cd6 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Thu, 21 Jan 2021 06:03:22 GMT Sender: saiprakash.ranjan=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id D9666C43461; Thu, 21 Jan 2021 06:03:21 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-caf-mail-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=ALL_TRUSTED,BAYES_00, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id D7656C433CA; Thu, 21 Jan 2021 06:03:20 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 21 Jan 2021 11:33:20 +0530 From: Sai Prakash Ranjan To: Mathieu Poirier Cc: Al Grant , Suzuki Poulose , Mike Leach , coresight@lists.linaro.org, Stephen Boyd , Denis Nikitin , linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, leo.yan@linaro.org, mnissler@google.com Subject: Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode tracing In-Reply-To: <20210120184839.GB708905@xps15> References: <20201015124522.1876-1-saiprakash.ranjan@codeaurora.org> <20201015160257.GA1450102@xps15> <20210118202354.GC464579@xps15> <32216e9fa5c9ffb9df1123792d40eafb@codeaurora.org> <20210120184839.GB708905@xps15> Message-ID: <45b0c83833ac0e2e8d231da3c4bb8e0e@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-01-21 00:18, Mathieu Poirier wrote: > On Tue, Jan 19, 2021 at 08:36:22AM +0000, Al Grant wrote: >> Hi Sai, >> >> > From: saiprakash.ranjan=codeaurora.org@mg.codeaurora.org >> > Hi Mathieu, >> > >> > On 2021-01-19 01:53, Mathieu Poirier wrote: >> > > On Fri, Jan 15, 2021 at 11:16:24AM +0530, Sai Prakash Ranjan wrote: >> > >> Hello Mathieu, Suzuki >> > >> >> > >> On 2020-10-15 21:32, Mathieu Poirier wrote: >> > >> > On Thu, Oct 15, 2020 at 06:15:22PM +0530, Sai Prakash Ranjan wrote: >> > >> > > On production systems with ETMs enabled, it is preferred to >> > >> > > exclude kernel mode(NS EL1) tracing for security concerns and >> > >> > > support only userspace(NS EL0) tracing. So provide an option via >> > >> > > kconfig to exclude kernel mode tracing if it is required. >> > >> > > This config is disabled by default and would not affect the >> > >> > > current configuration which has both kernel and userspace tracing >> > >> > > enabled by default. >> > >> > > >> > >> > >> > >> > One requires root access (or be part of a special trace group) to >> > >> > be able to use the cs_etm PMU. With this kind of elevated access >> > >> > restricting tracing at EL1 provides little in terms of security. >> > >> > >> > >> >> > >> Apart from the VM usecase discussed, I am told there are other >> > >> security concerns here regarding need to exclude kernel mode tracing >> > >> even for the privileged users/root. One such case being the ability >> > >> to analyze cryptographic code execution since ETMs can record all >> > >> branch instructions including timestamps in the kernel and there may >> > >> be other cases as well which I may not be aware of and hence have >> > >> added Denis and Mattias. Please let us know if you have any questions >> > >> further regarding this not being a security concern. >> > > >> > > Even if we were to apply this patch there are many ways to compromise >> > > a system or get the kernel to reveal important information using the >> > > perf subsystem. I would perfer to tackle the problem at that level >> > > rather than concentrating on coresight. >> > > >> > >> > Sorry but I did not understand your point. We are talking about the capabilities >> > of coresight etm tracing which has the instruction level tracing and a lot more. >> > Perf subsystem is just the framework used for it. >> > In other words, its not the perf subsystem which does instruction level tracing, >> > its the coresight etm. Why the perf subsystem should be modified to lockdown >> > kernel mode? If we were to let perf handle all the trace filtering for different >> > exception levels, then why do we need the register settings in coresight etm >> > driver to filter out NS EL* tracing? And more importantly, how do you suppose >> > we handle sysfs mode of coresight tracing with perf subsystem? >> >> You both have good points. Mathieu is right that this is not a >> CoreSight >> issue specifically, it is a matter of kernel security policy, and >> other hardware >> tracing mechanisms ought to be within its scope. There should be a >> general >> "anti kernel exfiltration" config that applies to all mechanisms >> within >> its scope, and we'd definitely expect that to include Intel PT as well >> as ETM. >> >> A kernel config that forced exclude_kernel on all perf events would >> deal with >> ETM and PT in one place, but miss the sysfs interface to ETM. >> >> On the other hand, doing it in the ETM drivers would cover the perf >> and sysfs >> interfaces to ETM, but would miss Intel PT. >> >> So I think what is needed is a general config option that is both >> implemented >> in perf (excluding all kernel tracing events) and by any drivers that >> provide >> an alternative interface to hardware tracing events. >> > > I also think this is the right solution. > Thanks for confirming, I will be working on this suggestion. Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation