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CVE-2026-89920: KVM: s390: Fix memory corruption by not reinjecting CK machine checks

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-16 · updated 2026-10-30

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: s390: Fix memory corruption by not reinjecting CK machine checks Channel-subsystem damage machine checks are for the host channel subsystem. The guest channel subsystem is emulated in the userspace VMM. There is no point in forwarding such machine checks into the guest. This also simplifies the machine check reinjection and avoids kfree of a stack variable as reported by sashiko. There might be still machine checks that have the ck bit set with another bit (like instruction damage), mask out the CK bit in s390_backup_mcck_info(), like the CP and ED bits already are.

Affected products

• Linux: 4.13 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux 7.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/045f3e95a0deccb277c29bd003e1d43c0ad40c90
• https://git.kernel.org/stable/c/546dde823a36d7283dcf46127c2f3d093443860f
• https://git.kernel.org/stable/c/5c63e2ed840c85e27172ab78e7db3ac77fba281b
• https://git.kernel.org/stable/c/6ee52d3af2a1bf70349cf3f860933c8d221e229a
• https://git.kernel.org/stable/c/7077ec953996acc04b49d1dfc43df1c1a2a74395
• https://git.kernel.org/stable/c/b7631982fb65dd355acd18e62b384bc8125e9c44

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