UBUNTU-CVE-2026-72412: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of PAGEUNUSED pte bit The PAGEUNUSED softbit should not really be lying around. Its sole purpose is to signal to trytounmapone() and trytomigrateone() that the page can be discarded instead of being moved / swapped. KVM has no way to know why a page is being unmapped, so it sets the bit on userspace ptes corresponding to unused guest pages every time they get unmapped. KVM has no reasonable way to clear the bit once the page is in use again. While setptes() checks and clears the bit, other paths that set new ptes did not. This led to used pages being thrown out as if they were unused, causing guest corruption. Fix the issue by clearing the PAGEUNUSED bit for present ptes in setpte(), i.e. whenever a present pte is getting set. The check in setptes() is then redundant and can be removed. Also fix gmaphelpertrysetpteunused() to only set the bit if the pte is present; the PAGEUNUSED bit is only defined for present ptes and thus should not be set for non-present ptes.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1013.13~24.04.1 - Upgrade
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ubuntu/linux-azure-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17~24.04.1 - Upgrade
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ubuntu/linux-azure-fde-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1016.16~24.04.1 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1013.13~24.04.1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-34.34~24.04.1 - Upgrade
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ubuntu/linux-nvidia-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1024.25~24.04.1 - Upgrade
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ubuntu/linux-oracle-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1012.12~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-34.34.1~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-34.34 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1007.8 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-nvidia-bosto a version that resolves this vulnerability.Fixed in 7.0.0-2022.23 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1012.12 - Upgrade
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ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 7.0.0-1020.20 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-34.34.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-34.34.1 - Compensating control
In the Linux kernel s390/mm code, update set_pte() to clear _PAGE_UNUSED whenever a present PTE is set, and update gmap_helper_try_set_pte_unused() to set _PAGE_UNUSED only when the PTE is present.
Event History
Frequently Asked Questions
Which systems are most likely to be affected?
The affected code is in the s390 memory-management path. The issue is relevant where KVM manages userspace page-table entries for guest pages that are unmapped and later used again.
What sequence leads to corruption?
KVM can mark a userspace PTE as unused when a guest page is unmapped, but cannot reliably clear that mark when the page is reused. If another path installs a present PTE without clearing the stale _PAGE_UNUSED bit, the used page may be discarded rather than moved or swapped.
What access does the published severity vector indicate?
The vector indicates local attack access, low privileges required, no user interaction, and additional attack conditions. It assigns no confidentiality impact, low integrity impact, and high availability impact.