We have just published Qubes Security Bulletin (QSB) 081: x86: MMIO Stale Data vulnerabilities (XSA-404). The text of this QSB is reproduced below. This QSB and its accompanying signatures will always be available in the Qubes Security Pack (qubes-secpack).
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---===[ Qubes Security Bulletin 081 ]===--- 2022-06-17 x86: MMIO Stale Data vulnerabilities (XSA-404) User action required --------------------- Users with appropriate hardware (see the "affected hardware" section below) must install the following specific packages in order to address the issues discussed in this bulletin: For Qubes 4.0, in dom0: - Xen packages, version 4.8.5-41 For Qubes 4.1, in dom0: - Xen packages, version 4.14.5-3 These packages will migrate from the security-testing repository to the current (stable) repository over the next two weeks after being tested by the community.  Once available, the packages are to be installed via the Qubes Update tool or its command-line equivalents.  Dom0 must be restarted afterward in order for the updates to take effect. If you use Anti Evil Maid, you will need to reseal your secret passphrase to new PCR values, as PCR18+19 will change due to the new Xen binaries. Summary -------- On 2022-06-14, the Xen Project published XSA-404, "x86: MMIO Stale Data vulnerabilities" : | This issue is related to the SRBDS, TAA and MDS vulnerabilities. | Please see: | | https://xenbits.xen.org/xsa/advisory-320.html (SRBDS) | https://xenbits.xen.org/xsa/advisory-305.html (TAA) | https://xenbits.xen.org/xsa/advisory-297.html (MDS) | | Please see Intel's whitepaper: | | https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/processor-mmio-stale-data-vulnerabilities.html Impact ------- An adversary who controls a VM with an assigned PCI device can infer the memory content of other guests or Xen itself. This could allow the adversary to read information that should be accessible only to Xen or another VM and to use that information to launch further attacks. In the default Qubes OS configuration, only sys-net and sys-usb can be used to perform this attack. Affected hardware ------------------ All Intel systems are affected. While mitigations are available, they are available only for some Intel CPU models. Normally, it should be a simple matter to look up a given CPU model number in a table to see whether it is affected and whether it is eligible for any mitigations. Indeed, Intel has published a table  that claims to serve this purpose. Unfortunately, however, we have found several inaccuracies in this table. Since we cannot rely on the table, we have had to devise an alternative method using other published Intel technical documents that appear to be more accurate. This has turned out to be quite complex. Our best evidence indicates that mitigations are available for all and only those CPUs that are both eligible for and updated with the Intel microcode update released in May 2022.  Since going through all the complicated technical steps of checking this manually would be excessively cumbersome for most users, we have written a tool that does it for you. Please note that this tool is entirely optional and is *not* required for any security updates to take effect. Rather, its intended purpose is to satisfy the curiosity of users who wish to know whether their own CPUs are eligible for mitigations and who would struggle to make that determination manually. This tool is included in the `qubes-core-dom0-linux-4.0.35` package for Qubes 4.0 and the `qubes-core-dom0-linux-4.1.23` package for Qubes 4.1. These packages will migrate from the security-testing repository to the current (stable) repository over the next two weeks after being tested by the community.  Once available, the packages are to be installed via the Qubes Update tool or its command-line equivalents.  After installing the required updates, you will be able to execute `sudo cpu-microcode-info` in a dom0 terminal. This will output a table of information about the logical CPUs (aka CPU "cores") in your system. The "F-M-S/PI" column lists the "Family-Model-Stepping/Platform ID" codes that Intel uses in its microcode documentation,  which is explained in further detail in Intel's README.  (The manual process of checking would involve extracting your CPU information, converting it to hexadecimal, and looking it up in the appropriate table in this document.) The "Loaded microcode version" column lists the microcode versions currently loaded for each CPU. The "20220510 update available" column lists whether the required May 2022 microcode update is *available* for each CPU. The "20220510 update installed" column lists whether the required May 2022 microcode update is *installed* in each CPU. In order for the updates associated with this bulletin to successfully mitigate XSA-404, a value of "yes" is required in both of these last two "20220510 update" columns. If the "available" column has a "yes" while the "installed" column has a "no," then the May 2022 microcode update must be installed first. If both columns have "no" values, then this CPU remains vulnerable, and there is no known mitigation available. If your system has such a CPU, then installing The Xen packages listed in the "user action required" section above is *not* expected to mitigate the problem described in this bulletin. Unfortunately, there is simply nothing we can do for these CPUs in terms of patching unless we receive a fix from Intel or receive new information about which CPUs are affected. Nonetheless, we still recommend installing the updates anyway (once available), since they will not make the problem any worse, keeping up-to-date with all security updates is a general best practice, and future updates will be based on the latest version. However, hope is not entirely lost for users whose CPUs are not eligible for software mitigations. Since the vulnerability discussed in this bulletin does not affect VMs without PCI passthrough devices, users still have the option of altering their habits to treat VMs like sys-usb and sys-net as more trusted. While this can be especially challenging in the case of sys-net, it at least affords users *some* latitude in working around the problem by being mindful of when such VMs are running, how trusted their templates are, and similar considerations. Further plans regarding PCI passthrough ---------------------------------------- This is yet another issue affecting only VMs with access to PCI devices. This pattern of vulnerabilities has prompted us to research more secure ways of handling such VMs in future Qubes releases. Eventually, we plan to treat them as more privileged VMs that require additional protection. Specific protective measures will be discussed with the community as part of our ongoing research and development efforts. Credits -------- See the original Xen Security Advisory. References -----------  https://www.qubes-os.org/doc/testing/  https://www.qubes-os.org/doc/how-to-update/  https://xenbits.xen.org/xsa/advisory-404.html  https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/processors-affected-consolidated-product-cpu-model.html  https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/blob/main/releasenote.md#microcode-20220510  https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files#about-processor-signature-family-model-stepping-and-platform-id -- The Qubes Security Team https://www.qubes-os.org/security/