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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 08E9CC433EF for ; Wed, 17 Nov 2021 11:54:09 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BA72E61154 for ; Wed, 17 Nov 2021 11:54:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org BA72E61154 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=3ayruJtl6pEJRXU9QRVH9BjeBGPtVYsMuJEsFc+E710=; b=I8M5rAV1ROyf0Q 92fvARwAUTmp2JrwYVFrS4fRFB5crC/FV/CwtLc6NgH7ZwdYUjpJHUhGeTNUIpTfYow2LlXVycqEt SR0NMhyC4rwN0Vf09p/aTkQQirm/1DUELYGrYjyy7kfeeTwE2x2TPr61obz+42M1GldCqH+6sQ6Tp MLbzjpI5HS07CJo+Vn/vgTZz/ptdYyPWJyaP1sTq4II2NNr+wZu9Ym6Kha2kjThjrAvrQHr+1joJ7 U/QFfFI1g1axVHg1mtsz7Xz/zz9BSZNKbjTAenC36lvA/GyY1oFfdCdy4WfcoLUNCma5YtOK5p3sS s2vsAyXNbxRCq9Pa9kuQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mnJUa-004ewr-4p; Wed, 17 Nov 2021 11:52:44 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mnJUV-004evb-Ml for linux-arm-kernel@lists.infradead.org; Wed, 17 Nov 2021 11:52:41 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2B860ED1; Wed, 17 Nov 2021 03:52:38 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.46.245]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 88A5A3F70D; Wed, 17 Nov 2021 03:52:36 -0800 (PST) Date: Wed, 17 Nov 2021 11:52:34 +0000 From: Mark Rutland To: Qian Cai Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, dvyukov@google.com, peterz@infradead.org, valentin.schneider@arm.com, will@kernel.org, woodylin@google.com Subject: Re: [PATCH] Reset task stack state in bringup_cpu() Message-ID: <20211117115234.GB41542@C02TD0UTHF1T.local> References: <20211115113310.35693-1-mark.rutland@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211117_035239_819445_075BB717 X-CRM114-Status: GOOD ( 23.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Nov 16, 2021 at 11:31:40AM -0500, Qian Cai wrote: > On Mon, Nov 15, 2021 at 11:33:10AM +0000, Mark Rutland wrote: > > To hot unplug a CPU, the idle task on that CPU calls a few layers of C > > code before finally leaving the kernel. When KASAN is in use, poisoned > > shadow is left around for each of the active stack frames, and when > > shadow call stacks are in use. When shadow call stacks are in use the > > task's SCS SP is left pointing at an arbitrary point within the task's > > shadow call stack. > > > > When an offlines CPU is hotlpugged back into the kernel, this stale > > state can adversely affect the newly onlined CPU. Stale KASAN shadow can > > alias new stackframes and result in bogus KASAN warnings. A stale SCS SP > > is effectively a memory leak, and prevents a portion of the shadow call > > stack being used. Across a number of hotplug cycles the task's entire > > shadow call stack can become unusable. > > > > We previously fixed the KASAN issue in commit: > > > > e1b77c92981a5222 ("sched/kasan: remove stale KASAN poison after hotplug") > > > > In commit: > > > > f1a0a376ca0c4ef1 ("sched/core: Initialize the idle task with preemption disabled") > > > > ... we broke both KASAN and SCS, with SCS being fixed up in commit: > > > > 63acd42c0d4942f7 ("sched/scs: Reset the shadow stack when idle_task_exit") > > > > ... but as this runs in the context of the idle task being offlines it's > > potentially fragile. > > > > Fix both of these consistently and more robustly by resetting the SCS SP > > and KASAN shadow immediately before we online a CPU. This ensures the > > idle task always has a consistent state, and removes the need to do so > > when initializing an idle task or when unplugging an idle task. > > > > I've tested this with both GCC and clang, with reelvant options enabled, > > offlining and online CPUs with: > > > > | while true; do > > | for C in /sys/devices/system/cpu/cpu*/online; do > > | echo 0 > $C; > > | echo 1 > $C; > > | done > > | done > > > > Link: https://lore.kernel.org/lkml/20211012083521.973587-1-woodylin@google.com/ > > Link: https://lore.kernel.org/linux-arm-kernel/YY9ECKyPtDbD9q8q@qian-HP-Z2-SFF-G5-Workstation/ > > Fixes: 1a0a376ca0c4ef1 ("sched/core: Initialize the idle task with preemption disabled") > > Reported-by: Qian Cai > > Signed-off-by: Mark Rutland > > Thanks for fixing this quickly, Mark. Triggering an user-after-free in > user namespace but don't think it is related. I'll investigate that > first since it is blocking the rest of regression testing. Cool; are you happy to provide a Tested-by tag for this patch? :) Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel