# CVE-2022-42336: xen: Mishandling of guest SSBD selection on AMD hardware The current logic to set SSBD on AMD Family 17h and Hygon Family...

CVE-2022-42336 is fixed in xen on 1 platform, first by DEBIAN-CVE-2022-42336, released May 17, 2023. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2022-42336
- Priority: Routine
- CVSS: 3.3 (low)
- EPSS: 0.0027
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 17, 2023

## Description

Mishandling of guest SSBD selection on AMD hardware The current logic to set SSBD on AMD Family 17h and Hygon Family 18h processors requires that the setting of SSBD is coordinated at a core level, as the setting is shared between threads. Logic was introduced to keep track of how many threads require SSBD active in order to coordinate it, such logic relies on using a per-core counter of threads that have SSBD active. When running on the mentioned hardware, it's possible for a guest to under or overflow the thread counter, because each write to VIRT_SPEC_CTRL.SSBD by the guest gets propagated to the helper that does the per-core active accounting. Underflowing the counter causes the value to get saturated, and thus attempts for guests running on the same core to set SSBD won't have effect because the hypervisor assumes it's already active.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | xen Debian 12.15 (bookworm) | 4.17.1+2-gb773c48e36-1 | [DEBIAN-CVE-2022-42336](https://patchblox.com/security/data/fix/linux/debian-cve-2022-42336.md) | May 17, 2023 |
| Linux | xen Debian 13.5 (trixie) | 4.17.1+2-gb773c48e36-1 | [DEBIAN-CVE-2022-42336](https://patchblox.com/security/data/fix/linux/debian-cve-2022-42336.md) | May 17, 2023 |
| Linux | xen Debian 14 | 4.17.1+2-gb773c48e36-1 | [DEBIAN-CVE-2022-42336](https://patchblox.com/security/data/fix/linux/debian-cve-2022-42336.md) | May 17, 2023 |

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