In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of _PAGE_UNUSED pte bit The _PAGE_UNUSED softbit should… (CVE-2026-72412)
In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of _PAGE_UNUSED pte bit The _PAGE_UNUSED softbit should not really be lying around. Its sole purpose is to signal to try_to_unmap_one() and try_to_migrate_one() 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 set_ptes() 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 _PAGE_UNUSED bit for present ptes in set_pte(), i.e. whenever a present pte is getting set. The check in set_ptes() is then redundant and can be removed. Also fix gmap_helper_try_set_pte_unused() to only set the bit if the pte is present; the _PAGE_UNUSED bit is only defined for present ptes and thus should not be set for non-present ptes.
In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of _PAGE_UNUSED pte bit The _PAGE_UNUSED softbit should… (CVE-2026-72412)
Description
In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of _PAGE_UNUSED pte bit The _PAGE_UNUSED softbit should not really be lying around. Its sole purpose is to signal to try_to_unmap_one() and try_to_migrate_one() 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 set_ptes() 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 _PAGE_UNUSED bit for present ptes in set_pte(), i.e. whenever a present pte is getting set. The check in set_ptes() is then redundant and can be removed. Also fix gmap_helper_try_set_pte_unused() to only set the bit if the pte is present; the _PAGE_UNUSED bit is only defined for present ptes and thus should not be set for non-present ptes.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-94jh-p9fj-qxf8
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-72412"]
- Ecosystems
- []
- Database Specific Severity
- null
- Cvss Version
- null
Threat ID: 6a808b6fbf8831d5394fa4e3
Added to database: 08/15/2026, 15:53:19 UTC
Last updated: 08/15/2026, 15:54:49 UTC
Views: 1
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