CVE-2026-64369

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Revert DCACHE_WORD_ACCESS Support in Linux Kernel

Publication date: 2026-07-25

Last updated on: 2026-08-11

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: s390: Revert support for DCACHE_WORD_ACCESS load_unaligned_zeropad() reads eight bytes from unaligned addresses and may cross page boundaries. It handles exceptions which may happen if reading from the second page results in an exception. For pages which are donated to the Ultravisor for secure execution purposes the do_secure_storage_access() exception handler however does not handle such exceptions correctly. Such an exception may result in an endless exception loop which will never be resolved. An attempt to fix this [1] turned out to be not sufficient. For now revert load_unaligned_zeropad() until this problem has been resolved in a proper way. Note that the implementation of load_unaligned_zeropad() itself is correct. The revert is just a temporary workaround until there is complete fix for secure storage access exceptions. [1] commit b00be77302d7 ("s390/mm: Add missing secure storage access fixups for donated memory")

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Meta Information

Published

2026-07-25

Last Modified

2026-08-11

Generated

2026-08-14

AI Q&A

2026-07-25

EPSS Evaluated

2026-08-13

NVD

CVE-2026-64369

EUVD

EUVD-2026-48913

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability affects the Linux kernel on s390 architecture. It involves a function called load_unaligned_zeropad() which reads eight bytes from unaligned memory addresses and may cross page boundaries. When handling exceptions from secure storage access, the system fails to resolve them correctly, leading to an endless exception loop.

Detection Guidance

This vulnerability is specific to the Linux kernel's s390 architecture and involves issues with load_unaligned_zeropad() and secure storage access. Detection requires checking kernel logs for exceptions related to DCACHE_WORD_ACCESS or secure storage access loops. Commands like dmesg or journalctl may show repeated exceptions or loops in kernel logs.

Impact Analysis

The vulnerability can cause system instability by triggering an endless exception loop. This may lead to crashes or unresponsive systems, particularly when secure storage access is involved. It does not directly expose data but disrupts normal operations.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards as it pertains to a low-level kernel memory access issue in the Linux s390 architecture. Compliance impacts would depend on system-specific implementations and mitigations rather than the vulnerability itself.

Mitigation Strategies

Immediate mitigation involves updating the Linux kernel to a patched version that reverts load_unaligned_zeropad() support for DCACHE_WORD_ACCESS. Check your distribution's security advisories for kernel updates. If no patch is available, consider disabling s390 architecture features temporarily until a fix is released.

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