From patchwork Fri Apr 17 11:54:46 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?b?SsO8cmdlbiBHcm/Dnw==?= X-Patchwork-Id: 227501 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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT 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 5E150C352BE for ; Fri, 17 Apr 2020 11:55:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42E1F2078E for ; Fri, 17 Apr 2020 11:55:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730474AbgDQLy7 (ORCPT ); Fri, 17 Apr 2020 07:54:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:40950 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730469AbgDQLy7 (ORCPT ); Fri, 17 Apr 2020 07:54:59 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 17549AFDC; Fri, 17 Apr 2020 11:54:57 +0000 (UTC) From: Juergen Gross To: security@xen.org Cc: Juergen Gross , =?utf-8?q?Marek_Marczykowski-G=C3=B3r?= =?utf-8?q?ecki?= , stable@vger.kernel.org Subject: [PATCH v3 1/9] xen/events: avoid removing an event channel while handling it Date: Fri, 17 Apr 2020 13:54:46 +0200 Message-Id: <20200417115454.24931-2-jgross@suse.com> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20200417115454.24931-1-jgross@suse.com> References: <20200417115454.24931-1-jgross@suse.com> MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Today it can happen that an event channel is being removed from the system while the event handling loop is active. This can lead to a race resulting in crashes or WARN() splats. Fix this problem by using a rwlock taken as reader in the event handling loop and as writer when removing an event channel. As the observed problem was a NULL dereference in evtchn_from_irq() make this function more robust against races by testing the irq_info pointer to be not NULL before dereferencing it. Cc: Marek Marczykowski-Górecki Cc: stable@vger.kernel.org Reported-by: Marek Marczykowski-Górecki Signed-off-by: Juergen Gross --- drivers/xen/events/events_base.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c index 3a791c8485d0..178a471906de 100644 --- a/drivers/xen/events/events_base.c +++ b/drivers/xen/events/events_base.c @@ -33,6 +33,7 @@ #include #include #include +#include #ifdef CONFIG_X86 #include @@ -70,6 +71,9 @@ const struct evtchn_ops *evtchn_ops; */ static DEFINE_MUTEX(irq_mapping_update_lock); +/* Lock protecting event handling loop against removing event channels. */ +static DEFINE_RWLOCK(evtchn_rwlock); + static LIST_HEAD(xen_irq_list_head); /* IRQ <-> VIRQ mapping. */ @@ -247,10 +251,14 @@ static void xen_irq_info_cleanup(struct irq_info *info) */ evtchn_port_t evtchn_from_irq(unsigned irq) { - if (WARN(irq >= nr_irqs, "Invalid irq %d!\n", irq)) + struct irq_info *info = NULL; + + if (likely(irq < nr_irqs)) + info = info_for_irq(irq); + if (WARN(!info, "Invalid irq %d!\n", irq)) return 0; - return info_for_irq(irq)->evtchn; + return info->evtchn; } unsigned int irq_from_evtchn(evtchn_port_t evtchn) @@ -603,6 +611,7 @@ static void __unbind_from_irq(unsigned int irq) { evtchn_port_t evtchn = evtchn_from_irq(irq); struct irq_info *info = irq_get_handler_data(irq); + unsigned long flags; if (info->refcnt > 0) { info->refcnt--; @@ -610,8 +619,10 @@ static void __unbind_from_irq(unsigned int irq) return; } + write_lock_irqsave(&evtchn_rwlock, flags); + if (VALID_EVTCHN(evtchn)) { - unsigned int cpu = cpu_from_irq(irq); + unsigned int cpu = cpu_from_irq(irq);; xen_evtchn_close(evtchn); @@ -629,6 +640,8 @@ static void __unbind_from_irq(unsigned int irq) xen_irq_info_cleanup(info); } + write_unlock_irqrestore(&evtchn_rwlock, flags); + xen_free_irq(irq); } @@ -1219,6 +1232,8 @@ static void __xen_evtchn_do_upcall(void) struct vcpu_info *vcpu_info = __this_cpu_read(xen_vcpu); int cpu = smp_processor_id(); + read_lock(&evtchn_rwlock); + do { vcpu_info->evtchn_upcall_pending = 0; @@ -1229,6 +1244,8 @@ static void __xen_evtchn_do_upcall(void) virt_rmb(); /* Hypervisor can set upcall pending. */ } while (vcpu_info->evtchn_upcall_pending); + + read_unlock(&evtchn_rwlock); } void xen_evtchn_do_upcall(struct pt_regs *regs)