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This article documents the Hypervisor-Specific Mitigations enablement process required to address Microarchitectural Data Sampling (MDS) Vulnerabilities identified by CVE-2018-12126, CVE-2018-12127, CVE-2018-12130, and CVE-2019-11091 in vSphere. In addition to the Hypervisor-Specific Mitigations described in this article, Hypervisor-Assisted Guest Mitigations and Operating System-Specific Mitigations are also required. These additional mitigations are documented VMSA-2019-0008. The Update History section of this article will be revised if there is a significant change. Click Subscribe to Article in the Actions box to be alerted when new information is added to this document and sign up at our Security-Announce mailing list to receive new and updated VMware Security Advisories.Introduction to MDS Intel has disclosed details on a new wave of speculative-execution vulnerabilities known collectively as “Microarchitectural Data Sampling (MDS)" that can occur on Intel microarchitecture prior to 2nd Generation Intel® Xeon® Scalable Processors (formerly known as Cascade Lake). These issues may allow a malicious user who can locally execute code on a system to infer the values of data otherwise protected by architectural mechanisms. Attack Vector Summary Sequential-context attack vector (Inter-VM): a malicious VM can potentially infer recently accessed data of a previous context (hypervisor thread or other VM thread) on either logical processor of a processor core. Concurrent-context attack vector (Inter-VM): a malicious VM can potentially infer recently accessed data of a concurrently executing context (hypervisor thread or other VM thread) on the other logical processor of the Hyper-Threading-enabled processor core. Mitigation Summary The Sequential-context attack vector (Inter-VM): is mitigated by a Hypervisor update to the product versions listed in VMSA-2019-0008 section 3a. These mitigations are dependent on Intel microcode updates (provided in separate ESXi patches for most Intel hardware platforms) also listed in the advisory. This mitigation is enabled by default and does not impose a significant performance impact. The Concurrent-context attack vector (Inter-VM): is mitigated through enablement of the ESXi Side-Channel-Aware Scheduler Version 1 or Version 2. These options may impose a non-trivial performance impact and are not enabled by default. Important: Disabling Intel Hyperthreading in firmware/BIOS (or by using VMkernel.Boot.Hyperthreading) after applying vSphere updates and patches is not recommended.
The Inter-VM mitigation process for MDS is divided into three phases: Update Phase: Apply vSphere Updates and Patches The Inter-VM Sequential-context attack vector is mitigated by a vSphere update to the product versions listed in VMware Security Advisory VMSA-2019-0008. This mitigation is dependent on Intel microcode updates (provided in separate ESXi patches for most Intel hardware platforms) which are also documented in VMSA-2019-0008. This mitigation is enabled by default and does not impose a significant performance impact. Note: As displayed in the workflow above, vCenter Server should be updated prior to applying ESXi patches. Notification messages were previously added in the patches to explain that the ESXi Side-Channel-Aware Scheduler must be enabled to mitigate Inter-VM Concurrent-context attack vectors. If ESXi is updated prior to vCenter you may receive cryptic notification messages relating to this. After vCenter has been updated, the notifications will be shown correctly. Planning Phase: Assess Your Environment Inter-VM Concurrent-context attack vectors are mitigated through enablement of the ESXi Side-Channel-Aware Scheduler which is included in the updates and patches listed in VMSA-2019-0008. This scheduler is not enabled by default. Enablement of this scheduler may impose a non-trivial performance impact on applications running in a vSphere environment. The goal of the Planning Phase is to understand if your current environment has sufficient CPU capacity to enable the scheduler without operational impact. The following list summarizes potential problem areas after enabling the ESXi Side-Channel-Aware Scheduler: VMs configured with vCPUs greater than the physical cores available on the ESXi host VMs configured with custom affinity or NUMA settings VMs with latency-sensitive configuration ESXi hosts with Average CPU Usage greater than 70% Hosts with custom CPU resource management options enabled HA Clusters where a rolling upgrade will increase Average CPU Usage above 100% Important: The above list is meant to be a brief overview of potential problem areas related to enablement of the ESXi Side-Channel-Aware Scheduler. The VMware Performance Team has provided an in-depth guide as well as performance data in KB55767. It is strongly suggested to thoroughly review this document prior to enablement of the scheduler. Note: It may be necessary to acquire additional hardware, or rebalance existing workloads, before enablement of the ESXi Side-Channel-Aware Scheduler. Organizations can choose not to enable the ESXi Side-Channel-Aware Scheduler after by accepting the risk posed by the Concurrent-context attack vector. This is NOT RECOMMENDED and VMware cannot make this decision on behalf of an organization. Scheduler-Enablement Phase: Enable the ESXi Side-Channel-Aware Scheduler in ESXi 5.5, 6.0, 6.5, and 6.7 prior to 6.7u2. After addressing the potential problem areas described above during the Planning Phase, the ESXi Side-Channel-Aware Scheduler must be enabled to mitigate Inter-VM Concurrent-context attack vectors. The scheduler can be enabled on an individual ESXi host via the advanced configuration option hyperthreadingMitigation. Note: Enabling this option will result in the vSphere UI reporting only a single logical processor per physical core; halving the number of logical processors if Hyperthreading was previously enabled. In addition Hyperthreading may be reported as 'Disabled' in various configuration tabs. Enabling the ESXi Side-Channel-Aware Scheduler using the vSphere Web Client or vSphere Client Connect to the vCenter Server using either the vSphere Web or vSphere Client. Select an ESXi host in the inventory. Click the Manage (5.5/6.0) or Configure (6.5/6.7) tab. Click the Settings sub-tab (5.5/6.0) or find the System section in the middle panel (6.5/6.7). Under the System heading, click Advanced System Settings. Click in the Filter box and search for VMkernel.Boot.hyperthreadingMitigation Select the setting by name and click the Edit pencil icon. Change the configuration option to true (default: false). Click OK. Reboot the ESXi host for the configuration change to go into effect. Enabling the ESXi Side-Channel-Aware Scheduler using ESXi Embedded Host Client Connect to the ESXi host by opening a web browser to https://HOSTNAME. Click the Manage tab.Click the Advanced settings sub-tab Click in the Filter box and search for VMkernel.Boot.hyperthreadingMitigation Select the setting by name and click the Edit pencil icon Change the configuration option to true (default: false) Click Save. Reboot the ESXi host for the configuration change to go into effect. Enable ESXi Side-Channel-Aware Scheduler setting using ESXCLI SSH to an ESXi host or open a console where the remote ESXCLI is installed. For more information, see the http://www.vmware.com/support/developer/vcli/Check the current runtime value of the HTAware Mitigation Setting by running esxcli system settings kernel list -o hyperthreadingMitigation To enable HT Aware Mitigation, run this command: esxcli system settings kernel set -s hyperthreadingMitigation -v TRUE Reboot the ESXi host for the configuration change to go into effect. Enable the ESXi Side-Channel-Aware Scheduler (SCAv1) or the ESXi Side-Channel-Aware Scheduler v2 (SCAv2) in ESXi 6.7u2 (13006603) or later Note: ESXi 6.7u2 (13006603) and future release lines of ESXi include the ESXi Side-Channel-Aware Scheduler v2. Prior release lines such as 6.5, 6.0, and 5.5 cannot accommodate this new scheduler. VMware has published a white paper entitled Performance of vSphere 6.7 Scheduling Options which provides a more detailed look into the performance differences between SCAv1 and SCAv2. Please review this document before continuing. Enabling the ESXi Side-Channel-Aware Scheduler (SCAv1) using the vSphere Web Client or vSphere Client Connect to the vCenter Server using either the vSphere Web or vSphere Client. Select an ESXi host in the inventory. Click the Configure tab.Under the System heading, click Advanced System Settings. Click Edit.Click in the Filter box and search for VMkernel.Boot.hyperthreadingMitigation Select the setting by name Change the configuration option to true (default: false). Click in the Filter box and search for VMkernel.Boot.hyperthreadingMitigationIntraVM Change the configuration option to true (default: true). Click OK.Reboot the ESXi host for the configuration change to go into effect. Enabling the ESXi Side-Channel-Aware Scheduler (SCAv1) using ESXi Embedded Host Client Connect to the ESXi host by opening a web browser to https://HOSTNAME. Click Manage under host navigator Click the Advanced settings Tab Use the search box to find VMkernel.Boot.hyperthreadingMitigation Select the VMkernel.Boot.hyperthreadingMitigation setting and click the Edit Option Change the configuration option to true (default: false) Click Save.Use the search box to find VMkernel.Boot.hyperthreadingMitigationIntraVMSelect the VMkernel.Boot.hyperthreadingMitigationIntraVM setting and click the Edit OptionChange the configuration option to true (default: true). Click Save.Reboot the ESXi host for the configuration change to go into effect. Enable ESXi Side-Channel-Aware Scheduler (SCAv1) using ESXCLI SSH to an ESXi host or open a console where the remote ESXCLI is installed. For more information, see the http://www.vmware.com/support/developer/vcli/. Check the current runtime values by running esxcli system settings kernel list -o hyperthreadingMitigation and esxcli system settings kernel list -o hyperthreadingMitigationIntraVM To enable the ESXi Side-Channel-Aware Scheduler Version 1, run these commands: esxcli system settings kernel set -s hyperthreadingMitigation -v TRUE esxcli system settings kernel set -s hyperthreadingMitigationIntraVM -v TRUE Reboot the ESXi host for the configuration change to go into effect. Enabling the ESXi Side-Channel-Aware Scheduler Version 2 (SCAv2) using the vSphere Web Client or vSphere Client Connect to the vCenter Server using either the vSphere Web or vSphere Client. Select an ESXi host in the inventory. Click the Configure tab. Under the System heading, click Advanced System Settings. Click Edit.Click in the Filter box and search for VMkernel.Boot.hyperthreadingMitigation Select the setting by name Change the configuration option to true (default: false). Click in the Filter box and search for VMkernel.Boot.hyperthreadingMitigationIntraVM Change the configuration option to false (default: true). Click OK.Reboot the ESXi host for the configuration change to go into effect. Enabling the ESXi Side-Channel-Aware Scheduler Version 2 (SCAv2) using ESXi Embedded Host Client Connect to the ESXi host by opening a web browser to https://HOSTNAME. Click Manage under host navigator Click the Advanced Settings tab Use the search box to find VMkernel.Boot.hyperthreadingMitigation Select the VMkernel.Boot.hyperthreadingMitigation setting and click the Edit option Change the configuration option to true (default: false) Click Save.Use the search box to find VMkernel.Boot.hyperthreadingMitigationIntraVM Select the VMkernel.Boot.hyperthreadingMitigationIntraVM setting and click the Edit option.Change the configuration option to false (default: true). Click Save.Reboot the ESXi host for the configuration change to go into effect. Enable ESXi Side-Channel-Aware Scheduler Version 2 (SCAv2) using ESXCLI SSH to an ESXi host or open a console where the remote ESXCLI is installed. For more information, see the http://www.vmware.com/support/developer/vcli/Check the current runtime values by running esxcli system settings kernel list -o hyperthreadingMitigation and esxcli system settings kernel list -o hyperthreadingMitigationIntraVM To enable the ESXi Side-Channel-Aware Scheduler Version 2 run these commands: esxcli system settings kernel set -s hyperthreadingMitigation -v TRUE esxcli system settings kernel set -s hyperthreadingMitigationIntraVM -v FALSE Reboot the ESXi host for the configuration change to go into effect. ESXi 6.7u2 (and later) Scheduler Configuration Summary hyperthreadingMitigation hyperthreadingMitigationIntraVM Scheduler Enabled FALSE TRUE or FALSE Default scheduler (unmitigated) TRUE TRUE SCAv1 TRUE FALSE SCAv2 HTAware Mitigation Tool VMware has provided a tool to assist in performing both the Planning Phase and the Scheduler-Enablement Phase at scale. This tool has been updated to include SCAv2 support and can be found in KB56931 along with detailed instructions on its usage, capabilities, and limitations. Table 1: Affected Intel Processors Supported by ESXi Intel Code Name FMS Intel Brand Names Nehalem-EP 0x106a5 Intel Xeon 35xx Series; Intel Xeon 55xx Series Lynnfield 0x106e5 Intel Xeon 34xx Lynnfield Series Clarkdale 0x20652 Intel i3/i5 Clarkdale Series; Intel Xeon 34xx Clarkdale Series Arrandale 0x20655 Intel Core i7-620LE Processor Sandy Bridge DT 0x206a7 Intel Xeon E3-1100 Series; Intel Xeon E3-1200 Series; Intel i7-2655-LE Series; Intel i3-2100 Series Westmere EP 0x206c2 Intel Xeon 56xx Series; Intel Xeon 36xx Series Sandy Bridge EP 0x206d7 Intel Pentium 1400 Series; Intel Xeon E5-1400 Series; Intel Xeon E5-1600 Series; Intel Xeon E5-2400 Series; Intel Xeon E5-2600 Series; Intel Xeon E5-4600 Series Nehalem EX 0x206e6 Intel Xeon 65xx Series; Intel Xeon 75xx Series Westmere EX 0x206f2 Intel Xeon E7-8800 Series; Intel Xeon E7-4800 Series; Intel Xeon E7-2800 Series Ivy Bridge DT 0x306a9 Intel i3-3200 Series; Intel i7-3500-LE/UE, Intel i7-3600-QE, Intel Xeon E3-1200-v2 Series; Intel Xeon E3-1100-C-v2 Series; Intel Pentium B925C Haswell DT 0x306c3 Intel Xeon E3-1200-v3 Series Ivy Bridge EP 0x306e4 Intel Xeon E5-4600-v2 Series; Intel Xeon E5-2400-v2 Series; Intel Xeon E5-2600-v2 Series; Intel Xeon E5-1400-v2 Series; Intel Xeon E5-2600-v2 Series Ivy Bridge EX 0x306e7 Intel Xeon E7-8800/4800/2800-v2 Series Haswell EP 0x306f2 Intel Xeon E5-2400-v3 Series; Intel Xeon E5-1400-v3 Series; Intel Xeon E5-1600-v3 Series; Intel Xeon E5-2600-v3 Series; Intel Xeon E5-4600-v3 Series Haswell EX 0x306f4 Intel Xeon E7-8800/4800-v3 Series Broadwell H 0x40671 Intel Core i7-5700EQ; Intel Xeon E3-1200-v4 Series Avoton 0x406d8 Intel Atom C2300 Series; Intel Atom C2500 Series; Intel Atom C2700 Series Broadwell EP/EX 0x406f1 Intel Xeon E7-8800/4800-v4 Series; Intel Xeon E5-4600-v4 Series; Intel Xeon E5-2600-v4 Series; Intel Xeon E5-1600-v4 Series Skylake SP 0x50654 Intel Xeon Platinum 8100 (Skylake-SP) Series; Intel Xeon Gold 6100/5100 (Skylake-SP) Series Intel Xeon Silver 4100, Bronze 3100 (Skylake-SP) Series Broadwell DE 0x50662 Intel Xeon D-1500 Series Broadwell DE 0x50663 Intel Xeon D-1500 Series Broadwell DE 0x50664 Intel Xeon D-1500 Series Broadwell NS 0x50665 Intel Xeon D-1500 Series Skylake H/S 0x506e3 Intel Xeon E3-1500-v5 Series; Intel Xeon E3-1200-v5 Series Kaby Lake H/S/X 0x906e9 Intel Xeon E3-1200-v6
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