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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 6734CC433DB for ; Fri, 15 Jan 2021 05:47:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1B250239FC for ; Fri, 15 Jan 2021 05:47:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732312AbhAOFrc (ORCPT ); Fri, 15 Jan 2021 00:47:32 -0500 Received: from m43-15.mailgun.net ([69.72.43.15]:62399 "EHLO m43-15.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730872AbhAOFra (ORCPT ); Fri, 15 Jan 2021 00:47:30 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1610689627; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=uKd60FvtWU74hmbEb+xSaAfRXFvIDWXHtourTMrbpIg=; b=Qub5SiFrK91He6a55DbzZfxC8QpBU2oQhsV8e3e+NgPhsrmtZz//a+k6ZwGuhS49lHENDD9q /YLbxOrA7Ilgqnz8xTsUF9VMOtHJFFapkFzT88vF4HedYEGck7jeoDqQ+gYimEUnfBFV3wCZ Hh1O1iUhk0Y1pZw+saH6KjKA/zM= X-Mailgun-Sending-Ip: 69.72.43.15 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-n10.prod.us-west-2.postgun.com with SMTP id 60012c323b6dceb1329ae0df (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Fri, 15 Jan 2021 05:46:26 GMT Sender: saiprakash.ranjan=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id ADD34C43461; Fri, 15 Jan 2021 05:46:25 +0000 (UTC) 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 17304C433CA; Fri, 15 Jan 2021 05:46:25 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Fri, 15 Jan 2021 11:16:24 +0530 From: Sai Prakash Ranjan To: Mathieu Poirier , Suzuki K Poulose Cc: 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, Al Grant , leo.yan@linaro.org, mnissler@google.com Subject: Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode tracing In-Reply-To: <20201015160257.GA1450102@xps15> References: <20201015124522.1876-1-saiprakash.ranjan@codeaurora.org> <20201015160257.GA1450102@xps15> Message-ID: 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 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. After this discussion, I would like to post a v2 based on Suzuki's feedback earlier. @Suzuki, I have a common config for ETM3 and ETM4 but couldn't get much idea on how to implement it for Intel PTs, if you have any suggestions there, please do share or we can have this only for Coresight ETMs. Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation