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=-6.6 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,T_DKIM_INVALID,URIBL_BLOCKED autolearn=ham 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 537A4ECE561 for ; Tue, 18 Sep 2018 06:09:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3B39204EC for ; Tue, 18 Sep 2018 06:09:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="QOYXGoHj"; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="cEl/OVUM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E3B39204EC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727404AbeIRLk3 (ORCPT ); Tue, 18 Sep 2018 07:40:29 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:41394 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726254AbeIRLk3 (ORCPT ); Tue, 18 Sep 2018 07:40:29 -0400 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 3850B60558; Tue, 18 Sep 2018 06:09:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1537250966; bh=t2vlNqcVKj13MR4CKgxUIzX4J2eZTym2aUZZIkt70Vw=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=QOYXGoHj6VS106UgrYZD9Cq+g4OvTaQ7Op5Wejhn+ewT5EeHtK1LOlQ6Uvn78S8lC 6af1n3W1uZqwjM412KDn471R50sWEJURb3hH9g1hvMy5zCE4scA79/cABoREgS59nm z7qCqcLuf4oMJlSywA1/AGNUbtxr2jDr3fkr+RGg= Received: from [10.79.129.80] (blr-bdr-fw-01_globalnat_allzones-outside.qualcomm.com [103.229.18.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan@smtp.codeaurora.org) by smtp.codeaurora.org (Postfix) with ESMTPSA id D2D846020A; Tue, 18 Sep 2018 06:09:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1537250965; bh=t2vlNqcVKj13MR4CKgxUIzX4J2eZTym2aUZZIkt70Vw=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=cEl/OVUMyR09M30LeRwv/g78SXESvHaMxo5zSTAUrnC12IyPdXBu7SJrU1xmuWOw3 86FWYWNbx5QXwVSuXusQkHOArbM47/VzeGDXAx1fuKaQDa1xnBmzAyguLtkRRev4WN GA3lkIgmbzEUVTplxPd5GSYMyIA1DLltvfYJZA90= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org D2D846020A Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=saiprakash.ranjan@codeaurora.org Subject: Re: [PATCH] tty/sysrq: Make local variable 'killer' in sysrq_handle_crash() global To: Matthias Kaehlcke , Greg Kroah-Hartman , Jiri Slaby Cc: linux-kernel@vger.kernel.org, Evan Green , Douglas Anderson , Stephen Boyd , Manoj Gupta , Nick Desaulniers References: <20180917213304.44476-1-mka@chromium.org> From: Sai Prakash Ranjan Message-ID: <98e5a46b-d7db-14c2-320e-f8f6c3c063bf@codeaurora.org> Date: Tue, 18 Sep 2018 11:39:20 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180917213304.44476-1-mka@chromium.org> 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 9/18/2018 3:03 AM, Matthias Kaehlcke wrote: > sysrq_handle_crash() dereferences a NULL pointer on purpose to force > an exception, the local variable 'killer' is assigned to NULL and > dereferenced later. Clang detects the NULL pointer dereference at compile > time and emits a BRK instruction (on arm64) instead of the expected NULL > pointer exception. Change 'killer' to a global variable (and rename it > to 'sysrq_killer' to avoid possible clashes) to prevent Clang from > detecting the condition. By default global variables are initialized > with zero/NULL in C, therefore an explicit initialization is not needed. > > Reported-by: Sai Prakash Ranjan > Suggested-by: Evan Green > Signed-off-by: Matthias Kaehlcke > --- > drivers/tty/sysrq.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c > index 06ed20dd01ba..49fa8e758690 100644 > --- a/drivers/tty/sysrq.c > +++ b/drivers/tty/sysrq.c > @@ -132,10 +132,10 @@ static struct sysrq_key_op sysrq_unraw_op = { > #define sysrq_unraw_op (*(struct sysrq_key_op *)NULL) > #endif /* CONFIG_VT */ > > +char *sysrq_killer; > + > static void sysrq_handle_crash(int key) > { > - char *killer = NULL; > - > /* we need to release the RCU read lock here, > * otherwise we get an annoying > * 'BUG: sleeping function called from invalid context' > @@ -144,7 +144,7 @@ static void sysrq_handle_crash(int key) > rcu_read_unlock(); > panic_on_oops = 1; /* force panic */ > wmb(); > - *killer = 1; > + *sysrq_killer = 1; > } > static struct sysrq_key_op sysrq_crash_op = { > .handler = sysrq_handle_crash, > Tested-by: Sai Prakash Ranjan -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation