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 9FEEAC43457 for ; Wed, 14 Oct 2020 09:36:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 377F12073A for ; Wed, 14 Oct 2020 09:36:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="rAgvuHcX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727826AbgJNJgs (ORCPT ); Wed, 14 Oct 2020 05:36:48 -0400 Received: from m42-4.mailgun.net ([69.72.42.4]:62370 "EHLO m42-4.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726361AbgJNJgs (ORCPT ); Wed, 14 Oct 2020 05:36:48 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1602668207; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=FTOEQCtqGMGUz2rk9/7VbauWsNvXRMhYgIKm7qBcvx8=; b=rAgvuHcXGKJYkhynlr3vH2LDSM/xbu024Tq+sgkqa+aAzMjhs7sZs60tIZ18+GEBQLi+TdTD kuQCBaljluG20lZ4O4e04GU2EFtHnhse6JcARyaVer1xgW8RbIEs62rBf4rHFQnQ2CJ830fr n2jH7f5Ab/dp2c/UjiYNziaVkd8= X-Mailgun-Sending-Ip: 69.72.42.4 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-n05.prod.us-east-1.postgun.com with SMTP id 5f86c69e3711fec7b15360b2 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Wed, 14 Oct 2020 09:36:30 GMT Sender: saiprakash.ranjan=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id CBEC4C4339C; Wed, 14 Oct 2020 09:36:29 +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 03487C433F1; Wed, 14 Oct 2020 09:36:28 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 14 Oct 2020 15:06:28 +0530 From: Sai Prakash Ranjan To: Suzuki K Poulose Cc: mathieu.poirier@linaro.org, mike.leach@linaro.org, coresight@lists.linaro.org, swboyd@chromium.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, denik@google.com, leo.yan@linaro.org, peterz@infradead.org Subject: Re: [PATCH 1/2] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf() In-Reply-To: <5bbb2d35-3e56-56d7-4722-bf34c5efa2fb@arm.com> References: <5bbb2d35-3e56-56d7-4722-bf34c5efa2fb@arm.com> Message-ID: <9fa4fcc25dac17b343d151a9d089b48c@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 2020-10-13 22:05, Suzuki K Poulose wrote: > On 10/07/2020 02:00 PM, Sai Prakash Ranjan wrote: >> There was a report of NULL pointer dereference in ETF enable >> path for perf CS mode with PID monitoring. It is almost 100% >> reproducible when the process to monitor is something very >> active such as chrome and with ETF as the sink and not ETR. >> Currently in a bid to find the pid, the owner is dereferenced >> via task_pid_nr() call in tmc_enable_etf_sink_perf() and with >> owner being NULL, we get a NULL pointer dereference. >> >> Looking at the ETR and other places in the kernel, ETF and the >> ETB are the only places trying to dereference the task(owner) >> in tmc_enable_etf_sink_perf() which is also called from the >> sched_in path as in the call trace. Owner(task) is NULL even >> in the case of ETR in tmc_enable_etr_sink_perf(), but since we >> cache the PID in alloc_buffer() callback and it is done as part >> of etm_setup_aux() when allocating buffer for ETR sink, we never >> dereference this NULL pointer and we are safe. So lets do the > > The patch is necessary to fix some of the issues. But I feel it is > not complete. Why is it safe earlier and not later ? I believe we are > simply reducing the chances of hitting the issue, by doing this earlier > than > later. I would say we better fix all instances to make sure that the > event->owner is valid. (e.g, I can see that the for kernel events > event->owner == -1 ?) > > struct task_struct *tsk = READ_ONCE(event->owner); > > if (!tsk || is_kernel_event(event)) > /* skip ? */ > Looking at it some more, is_kernel_event() is not exposed outside events core and probably for good reason. Why do we need to check for this and not just tsk? Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation