CVE-2025-38733: s390/mm: Do not map lowcore with identity mapping

Severity: medium (CVSS 5.5 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: 2025-09-05 · updated 2026-10-19
Weakness: CWE-476

Description

In the Linux kernel, the following vulnerability has been resolved: s390/mm: Do not map lowcore with identity mapping Since the identity mapping is pinned to address zero the lowcore is always also mapped to address zero, this happens regardless of the relocate_lowcore command line option. If the option is specified the lowcore is mapped twice, instead of only once. This means that NULL pointer accesses will succeed instead of causing an exception (low address protection still applies, but covers only parts). To fix this never map the first two pages of physical memory with the identity mapping.

Affected products

Linux kernel: from 6.10.11 before 6.11; from 6.11.1 before 6.12.44; from 6.13 before 6.16.4; 6.11, 6.11-rc5, 6.11-rc6, 6.11-rc7, 6.17-rc1, 6.17-rc2 — fixed in 6.11, 6.12.44, 6.16.4

How to fix

Upgrade to a fixed version: Linux kernel 6.11, 6.12.44, 6.16.4. Check the vendor advisory for mitigations.

References

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