Google: sys-kernel/cchost-kernel-6_18, sys-kernel/csql-kernel-6_18, sys-kernel/lakitu-kernel-6_18, sys-kernel/lakitu-nc-kernel-6_18: security update to 20198.0.0

medium Tenable Cloud Security Plugin ID 475671

Description

There are packages installed that are affected by a vulnerability referenced in the following CVE:

- In the Linux kernel, the following vulnerability has been resolved: x86/mm: Fix user-space data loss with
MADV_FREE and THP Some of users of Polars (a data analytics library) have lost production data from this
bug. They seem to have just the right combination of huge pages, MADV_FREE and heavy reclaim pressure.
pmd_modify() masks the old value with (_HPAGE_CHG_MASK & ~_PAGE_DIRTY), silently discarding the hardware
dirty bit. The subsequent pmd_mksaveddirty() call is supposed to transfer _PAGE_DIRTY into
_PAGE_SAVED_DIRTY when write-protecting, but the dirty bit was already stripped from the value, so there
is nothing left to transfer. Contrast with pte_modify(), which keeps _PAGE_DIRTY_BITS in its mask, and
pud_modify(), which keeps _HPAGE_CHG_MASK untouched: pmd_modify() is the odd one out. Any pmd_modify() on
a writable, dirty PMD loses the dirty state. One visible consequence is data loss with MADV_FREE on PMD-
mapped THP: memset(buf, 0x5A, size); // PMD-mapped THP, PMD dirty madvise(buf, size, MADV_FREE); // PMD
cleaned but left writable, // folio marked lazyfree memset(buf, 0x5A, size); // hardware sets _PAGE_DIRTY
again mprotect(buf, size, PROT_READ); // pmd_modify() drops the dirty bit mprotect(buf, size,
PROT_READ|PROT_WRITE); // ... memory pressure ... Reclaim (e.g. under memcg pressure) then finds the
lazyfree folio with no dirty bit set anywhere and frees it in __discard_anon_folio_pmd_locked(), even
though the data was rewritten after MADV_FREE; subsequent reads fault in fresh zero pages. NUMA hinting
alone can trigger the same loss, as do_huge_pmd_numa_page() restores the PMD through pmd_modify() as well.
PMD-mapped file THPs are affected too: mprotect()/NUMA hinting dropping the dirty bit means rewritten data
is never written back. Fix it by keeping _PAGE_DIRTY in the preserved mask, exactly like pte_modify() and
pud_modify() do. The existing pmd_mksaveddirty()/pmd_clear_saveddirty() pair then performs the hardware-
dirty <-> saved-dirty transition based on the write bit, preserving the shadow-stack encoding rules.
(CVE-2026-97945)

Solution

Update the sys-kernel/cchost-kernel-6_18 library and its related packages to version 20198.0.0 or later.

Plugin Details

Severity: Medium

ID: 475671

Version: Revision 1.1

Type: Local

Family: Google COS Security Checks

Published: 10/16/2026

Updated: 10/16/2026

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.6

Vendor

Vendor Severity: LOW

CVSS v2

Risk Factor: Medium

Base Score: 4.6

Temporal Score: 3.4

Vector: CVSS2#AV:L/AC:L/Au:S/C:N/I:N/A:C

CVSS Score Source: CVE-2026-97945

CVSS v3

Risk Factor: Medium

Base Score: 5.5

Temporal Score: 4.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 9/25/2026

Reference Information

CVE: CVE-2026-97945

Detections

Analytics