CVE-2026-31466

mm/huge_memory: fix folio isn't locked in softleaf_to_folio()

Published Apr 22, 2026 CVSS 3.1 · 4.7 Medium EPSS < 1% KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:

mm/huge_memory: fix folio isn't locked in softleaf_to_folio()

On arm64 server, we found folio that get from migration entry isn't locked
in softleaf_to_folio(). This issue triggers when mTHP splitting and
zap_nonpresent_ptes() races, and the root cause is lack of memory barrier
in softleaf_to_folio(). The race is as follows:

CPU0 CPU1

deferred_split_scan() zap_nonpresent_ptes()
lock folio
split_folio()
unmap_folio()
change ptes to migration entries
__split_folio_to_order() softleaf_to_folio()
set flags(including PG_locked) for tail pages folio = pfn_folio(softleaf_to_pfn(entry))
smp_wmb() VM_WARN_ON_ONCE(!folio_test_locked(folio))
prep_compound_page() for tail pages

In __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages
are visible before the tail page becomes non-compound. smp_wmb() should
be paired with smp_rmb() in softleaf_to_folio(), which is missed. As a
result, if zap_nonpresent_ptes() accesses migration entry that stores tail
pfn, softleaf_to_folio() may see the updated compound_head of tail page
before page->flags.

This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio()
because of the race between folio split and zap_nonpresent_ptes()
leading to a folio incorrectly undergoing modification without a folio
lock being held.

This is a BUG_ON() before commit 93976a20345b ("mm: eliminate further
swapops predicates"), which in merged in v6.19-rc1.

To fix it, add missing smp_rmb() if the softleaf entry is migration entry
in softleaf_to_folio() and softleaf_to_page().

[tujinjiang@huawei.com: update function name and comments]

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4561-1 linux-6.1 security update
Debian DLA Debian DLA DLA-4606-1 linux security update
Debian DSA Debian DSA DSA-6238-1 linux security update
Debian DSA Debian DSA DSA-6243-1 linux security update
Ubuntu USN Ubuntu USN USN-8567-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8574-1 Linux kernel (GCP FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8575-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8576-1 Linux kernel (NVIDIA Tegra) vulnerabilities
Ubuntu USN Ubuntu USN USN-8574-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8595-1 Linux kernel (Oracle) vulnerabilities
Ubuntu USN Ubuntu USN USN-8596-1 Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-8575-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8576-2 Linux kernel (NVIDIA Tegra) vulnerabilities
Ubuntu USN Ubuntu USN USN-8597-1 Linux kernel (IBM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8575-3 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8595-2 Linux kernel (AWS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8606-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8607-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8608-1 Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8609-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8610-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8574-3 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8595-3 Linux kernel (AWS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8619-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-8620-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8620-2 Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8620-3 Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN Ubuntu USN USN-8620-4 Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN Ubuntu USN USN-8665-1 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-8668-1 Linux kernel (GCP) vulnerabilities
Ubuntu USN Ubuntu USN USN-8668-2 Linux kernel (Raspberry Pi) vulnerabilities
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Weaknesses CWE-362
CPEs cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*
Metrics cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

Type Values Removed Values Added
Weaknesses CWE-366
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Low

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: mm/huge_memory: fix folio isn't locked in softleaf_to_folio() On arm64 server, we found folio that get from migration entry isn't locked in softleaf_to_folio(). This issue triggers when mTHP splitting and zap_nonpresent_ptes() races, and the root cause is lack of memory barrier in softleaf_to_folio(). The race is as follows: CPU0 CPU1 deferred_split_scan() zap_nonpresent_ptes() lock folio split_folio() unmap_folio() change ptes to migration entries __split_folio_to_order() softleaf_to_folio() set flags(including PG_locked) for tail pages folio = pfn_folio(softleaf_to_pfn(entry)) smp_wmb() VM_WARN_ON_ONCE(!folio_test_locked(folio)) prep_compound_page() for tail pages In __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages are visible before the tail page becomes non-compound. smp_wmb() should be paired with smp_rmb() in softleaf_to_folio(), which is missed. As a result, if zap_nonpresent_ptes() accesses migration entry that stores tail pfn, softleaf_to_folio() may see the updated compound_head of tail page before page->flags. This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio() because of the race between folio split and zap_nonpresent_ptes() leading to a folio incorrectly undergoing modification without a folio lock being held. This is a BUG_ON() before commit 93976a20345b ("mm: eliminate further swapops predicates"), which in merged in v6.19-rc1. To fix it, add missing smp_rmb() if the softleaf entry is migration entry in softleaf_to_folio() and softleaf_to_page(). [tujinjiang@huawei.com: update function name and comments]
Title mm/huge_memory: fix folio isn't locked in softleaf_to_folio()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Nov 10, 2026, 12:44 PM
Reserved
Mar 9, 2026, 3:48 PM
Status
Modified
Published
Apr 22, 2026, 2:16 PM
Modified
Nov 11, 2026, 11:10 PM
Severity
Low
Public date
Apr 22, 2026, 12:00 AM