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 C8F83C433EF for ; Mon, 15 Nov 2021 11:33:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A2F2761C15 for ; Mon, 15 Nov 2021 11:33:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229962AbhKOLgY (ORCPT ); Mon, 15 Nov 2021 06:36:24 -0500 Received: from foss.arm.com ([217.140.110.172]:54250 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230126AbhKOLgT (ORCPT ); Mon, 15 Nov 2021 06:36:19 -0500 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 EB04B6D; Mon, 15 Nov 2021 03:33:21 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 963D63F70D; Mon, 15 Nov 2021 03:33:20 -0800 (PST) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: catalin.marinas@arm.com, dvyukov@google.com, mark.rutland@arm.com, peterz@infradead.org, quic_qiancai@quicinc.com, valentin.schneider@arm.com, will@kernel.org, woodylin@google.com Subject: [PATCH] Reset task stack state in bringup_cpu() Date: Mon, 15 Nov 2021 11:33:10 +0000 Message-Id: <20211115113310.35693-1-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: Catalin Marinas Cc: Dmitry Vyukov Cc: Peter Zijlstra Cc: Valentin Schneider Cc: Will Deacon Cc: Woody Lin --- kernel/cpu.c | 7 +++++++ kernel/sched/core.c | 4 ---- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/cpu.c b/kernel/cpu.c index 192e43a87407..407a2568f35e 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -31,6 +31,7 @@ #include #include #include +#include #include #include @@ -588,6 +589,12 @@ static int bringup_cpu(unsigned int cpu) int ret; /* + * Reset stale stack state from the last time this CPU was online. + */ + scs_task_reset(idle); + kasan_unpoison_task_stack(idle); + + /* * Some architectures have to walk the irq descriptors to * setup the vector space for the cpu which comes online. * Prevent irq alloc/free across the bringup. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3c9b0fda64ac..76f9deeaa942 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8619,9 +8619,6 @@ void __init init_idle(struct task_struct *idle, int cpu) idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY; kthread_set_per_cpu(idle, cpu); - scs_task_reset(idle); - kasan_unpoison_task_stack(idle); - #ifdef CONFIG_SMP /* * It's possible that init_idle() gets called multiple times on a task, @@ -8777,7 +8774,6 @@ void idle_task_exit(void) finish_arch_post_lock_switch(); } - scs_task_reset(current); /* finish_cpu(), as ran on the BP, will clean up the active_mm state */ } -- 2.11.0