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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9102CC433EF for ; Thu, 10 Mar 2022 10:03:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240832AbiCJKEy (ORCPT ); Thu, 10 Mar 2022 05:04:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43020 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231982AbiCJKEy (ORCPT ); Thu, 10 Mar 2022 05:04:54 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 57C14D31C8 for ; Thu, 10 Mar 2022 02:03:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646906630; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xoEM/zTIrA+ouqqkKilQrOU6RwpehsCB4XrQR1QepKk=; b=UNxCFxloHb13cwsAC1nbP+ER3sUigKltAYEtzO1oWj336gY3/bVOxAH0NBHbsiIs/H0xk8 3KptAQCOqAPfoM3EKdRDw0/rHcgYzqFTueiNfdLHnvKSTIrUU1Qa8cojQqav0sBv+48ARe xbPLwK6HuT59wDgRiZeI5Soxddiwr0E= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-622-jKPEPVuMNaqr-75wMDCglQ-1; Thu, 10 Mar 2022 05:03:49 -0500 X-MC-Unique: jKPEPVuMNaqr-75wMDCglQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 18AE9801AB2; Thu, 10 Mar 2022 10:03:48 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.68]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B172B100692D; Thu, 10 Mar 2022 10:03:34 +0000 (UTC) Date: Thu, 10 Mar 2022 10:03:31 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Chenyi Qiang Cc: Paolo Bonzini , Richard Henderson , Eduardo Habkost , Marcelo Tosatti , Xiaoyao Li , kvm@vger.kernel.org, qemu-devel@nongnu.org Subject: Re: [PATCH 2/2] i386: Add notify VM exit support Message-ID: Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20220310090205.10645-1-chenyi.qiang@intel.com> <20220310090205.10645-3-chenyi.qiang@intel.com> <43c55ff9-eab6-7dc5-c634-9817b5a523cd@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <43c55ff9-eab6-7dc5-c634-9817b5a523cd@intel.com> User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Mar 10, 2022 at 05:53:05PM +0800, Chenyi Qiang wrote: > > > On 3/10/2022 5:17 PM, Daniel P. BerrangĂ© wrote: > > On Thu, Mar 10, 2022 at 05:02:05PM +0800, Chenyi Qiang wrote: > > > There are cases that malicious virtual machine can cause CPU stuck (due > > > to event windows don't open up), e.g., infinite loop in microcode when > > > nested #AC (CVE-2015-5307). No event window means no event (NMI, SMI and > > > IRQ) can be delivered. It leads the CPU to be unavailable to host or > > > other VMs. Notify VM exit is introduced to mitigate such kind of > > > attacks, which will generate a VM exit if no event window occurs in VM > > > non-root mode for a specified amount of time (notify window). > > > > > > A new KVM capability KVM_CAP_X86_NOTIFY_VMEXIT is exposed to user space > > > so that the user can query the capability and set the expected notify > > > window when creating VMs. > > > > > > If notify VM exit happens with VM_INVALID_CONTEXT, hypervisor should > > > exit to user space with the exit reason KVM_EXIT_NOTIFY to inform the > > > fatal case. Then user space can inject a SHUTDOWN event to the target > > > vcpu. This is implemented by defining a new bit in flags field of > > > kvm_vcpu_event in KVM_SET_VCPU_EVENTS ioctl. > > > > > > Signed-off-by: Chenyi Qiang > > > --- > > > hw/i386/x86.c | 24 ++++++++++++++++++ > > > include/hw/i386/x86.h | 3 +++ > > > target/i386/kvm/kvm.c | 58 ++++++++++++++++++++++++++++--------------- > > > 3 files changed, 65 insertions(+), 20 deletions(-) > > > > > > diff --git a/hw/i386/x86.c b/hw/i386/x86.c > > > index b84840a1bb..25e6c50b1e 100644 > > > --- a/hw/i386/x86.c > > > +++ b/hw/i386/x86.c > > > @@ -1309,6 +1309,23 @@ static void machine_set_sgx_epc(Object *obj, Visitor *v, const char *name, > > > qapi_free_SgxEPCList(list); > > > } > > > +static void x86_machine_get_notify_window(Object *obj, Visitor *v, > > > + const char *name, void *opaque, Error **errp) > > > +{ > > > + X86MachineState *x86ms = X86_MACHINE(obj); > > > + int32_t notify_window = x86ms->notify_window; > > > + > > > + visit_type_int32(v, name, ¬ify_window, errp); > > > +} > > > + > > > +static void x86_machine_set_notify_window(Object *obj, Visitor *v, > > > + const char *name, void *opaque, Error **errp) > > > +{ > > > + X86MachineState *x86ms = X86_MACHINE(obj); > > > + > > > + visit_type_int32(v, name, &x86ms->notify_window, errp); > > > +} > > > + > > > static void x86_machine_initfn(Object *obj) > > > { > > > X86MachineState *x86ms = X86_MACHINE(obj); > > > @@ -1319,6 +1336,7 @@ static void x86_machine_initfn(Object *obj) > > > x86ms->oem_id = g_strndup(ACPI_BUILD_APPNAME6, 6); > > > x86ms->oem_table_id = g_strndup(ACPI_BUILD_APPNAME8, 8); > > > x86ms->bus_lock_ratelimit = 0; > > > + x86ms->notify_window = -1; > > > } > > > > IIUC from the kernel patch, this negative value leaves the protection > > disabled, and thus the host remains vulnerable to the CVE. I would > > expect this ought to set a suitable default value to fix the flaw. > > > > Hum, I missed some explanation in commit message. > We had some discussion about the default behavior of this feature. There are > some concerns. e.g. > There's a possibility, however small, that a notify VM exit happens > with VM_CONTEXT_INVALID set in exit qualification, which means VM > context is corrupted. To avoid the false positive and a well-behaved > guest gets killed, we decide to make this feature opt-in. That is unfortunate. It is not going to be much benefit to add this feature, if users are discouraged from using it because of the danger of it killing non-malicious guests :-( Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|