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Andrew Cooper
3c04c258ab
The Microarchitectural Data Sampling vulnerability is split into categories with subtly different properties: MLPDS - Microarchitectural Load Port Data Sampling MSBDS - Microarchitectural Store Buffer Data Sampling MFBDS - Microarchitectural Fill Buffer Data Sampling MDSUM - Microarchitectural Data Sampling Uncacheable Memory MDSUM is a special case of the other three, and isn't distinguished further. These issues pertain to three microarchitectural buffers. The Load Ports, the Store Buffers and the Fill Buffers. Each of these structures are flushed by the new enhanced VERW functionality, but the conditions under which flushing is necessary vary. For this concise overview of the issues and default logic, the abbreviations SP (Store Port), FB (Fill Buffer), LP (Load Port) and HT (Hyperthreading) are used for brevity: * Vulnerable hardware is divided into two categories - parts which suffer from SP only, and parts with any other combination of vulnerabilities. * SP only has an HT interaction when the thread goes idle, due to the static partitioning of resources. LP and FB have HT interactions at all points, due to the competitive sharing of resources. All issues potentially leak data across the return-to-guest transition. * The microcode which implements VERW flushing also extends MSR_FLUSH_CMD, so we don't need to do both on the HVM return-to-guest path. However, some parts are not vulnerable to L1TF (therefore have no MSR_FLUSH_CMD), but are vulnerable to MDS, so do require VERW on the HVM path. Note that we deliberately support mds=1 even without MD_CLEAR in case the microcode has been updated but the feature bit not exposed. This is part of XSA-297, CVE-2018-12126, CVE-2018-12127, CVE-2018-12130, CVE-2019-11091. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>
Remus provides fault tolerance for virtual machines by sending continuous checkpoints to a backup, which will activate if the target VM fails. See the website at http://wiki.xen.org/wiki/Remus for details. Using Remus with libxl on Xen 4.5 and higher: To enable network buffering, you need libnl 3.2.8 or higher along with the development headers and command line utilities. If your distro does not have the appropriate libnl3 version, you can find the latest source tarball of libnl3 at http://www.carisma.slowglass.com/~tgr/libnl/ Disk replication: VMs protected by Remus need to use DRBD based disk backends. Specifically, you need a compile and install a custom version of DRBD, that is available publicly at https://github.com/rshriram/remus-drbd This code is based on DRBD 8.3.11 and uses a new replication protocol (named protocol D) for asynchronous disk checkpoint replication. A protected VM's DRBD disks on the primary and backup hosts need to be configured to use protocol D as the replication protocol. An example resource configuration file can be found in the aforementioned github repository.