In the Linux kernel, the following vulnerability has been resolved: KVM: s390: Fix _gaccess_shadow_fault() In some circumstances, it is possible… (CVE-2026-98653)

The Linux kernel KVM s390 vulnerability (CVE-2026-98653) involves a flaw in the _gaccess_shadow_fault() function where, under certain conditions, a nested guest memory page that should be shadowed is absent from the parent guest's gmap. This causes dat_entry_walk() to return -ENOENT, an error that is incorrectly propagated to userspace. The patch corrects this by explicitly invoking gmap_link() on the nested guest memory if the mapping is not already present, ensuring proper handling of shadowed memory pages.

The vulnerability causes incorrect error propagation when accessing nested guest memory in the KVM s390 virtualization environment. This could potentially disrupt nested virtualization operations by causing unexpected failures in memory access handling. No information is provided about exploitation or broader impact beyond this error propagation.

A fix has been implemented to address this vulnerability by modifying the _gaccess_shadow_fault() function to manually call gmap_link() when necessary. Users should apply the official Linux kernel patch that resolves this issue. Since this is a kernel-level fix, updating to the patched kernel version is the recommended remediation.