---
id: CVE-2026-80893
title: 'mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork()

  copy_hugetlb_page_range() clears the uffd-wp bit of migration and hwpoison
  entries with huge_pte_…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 <
    f1b1311c0352873137768bac5a126e491271a747
  - >-
    Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 <
    69cb5825d9988c7944bc9f1dc08cb233655405a7
  - >-
    Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 <
    8b0de7005b148738d79d6c45594d566489948a68
  - >-
    Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 <
    2b9a07002c2f296aa6a9c591213933d3492e3089
  - >-
    Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 <
    2fa11c60c9c06bafc19cf4d9efdaa36a38079e87
  - >-
    Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 <
    83abe2fd5b3aeb3123b5408a5a91709c5538fb23
  - Linux 5.19
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-06T17:04:44.937840Z'
published: '2026-09-04'
updated: '2026-11-06'
sourceUpdated: '2026-11-06T17:05:56.363Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-80893'
references:
  - url: 'https://git.kernel.org/stable/c/f1b1311c0352873137768bac5a126e491271a747'
  - url: 'https://git.kernel.org/stable/c/69cb5825d9988c7944bc9f1dc08cb233655405a7'
  - url: 'https://git.kernel.org/stable/c/8b0de7005b148738d79d6c45594d566489948a68'
  - url: 'https://git.kernel.org/stable/c/2b9a07002c2f296aa6a9c591213933d3492e3089'
  - url: 'https://git.kernel.org/stable/c/2fa11c60c9c06bafc19cf4d9efdaa36a38079e87'
  - url: 'https://git.kernel.org/stable/c/83abe2fd5b3aeb3123b5408a5a91709c5538fb23'
tags:
  - cve.org
epss: 0.00173
epssPercentile: 0.06691
ingestedAt: '2026-11-06T18:00:12.526Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork()

copy_hugetlb_page_range() clears the uffd-wp bit of migration and hwpoison
entries with huge_pte_clear_uffd_wp(), which operates on the present-PTE
bit position.  Swap entries keep the uffd-wp state elsewhere -- the
migration branch reads and sets it with pte_swp_uffd_wp() and
pte_swp_mkuffd_wp() -- and the present-PTE position falls into the swap
payload.  On x86-64 it lands in the inverted swap offset, where a
naturally-aligned hugetlb PFN always has the affected bit set, so the
clear advances the encoded PFN by two pages.

No userfaultfd needs to be involved: the clear is guarded only by the
child VMA not being uffd-wp registered, so a plain fork() with an
in-flight hugetlb migration entry (or a poisoned hugetlb page) corrupts
the entry copied into the child.  Instrumenting the clear and forking
after MADV_HWPOISON on a 2MB anon hugetlb page shows:

  offset before=120e00
  offset after =120e02

The fallout is mostly latent: rmap walks match migration entries by folio
range and remove_migration_pte() rebuilds the PTE from the folio, so a
within-folio PFN skew heals once migration completes.  But any path that
re-encodes the corrupted offset -- e.g.  hugetlb_change_protection()
rewriting a writable migration entry via
make_readable_migration_entry(swp_offset(entry)) -- propagates it.

Migration entries legitimately carry uffd-wp, so clear it with
pte_swp_clear_uffd_wp(), matching copy_nonpresent_pte() and
move_huge_pte().

A hwpoison entry, on the other hand, never carries the uffd-wp bit: it is
installed fresh by make_hwpoison_entry() (try_to_unmap_one() does not
preserve uffd-wp on the hwpoison path) and hugetlb_change_protection()
leaves hwpoison entries untouched.  There was nothing to clear there, only
the corruption, so drop the clear entirely.

## Affected

- `Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 < f1b1311c0352873137768bac5a126e491271a747`
- `Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 < 69cb5825d9988c7944bc9f1dc08cb233655405a7`
- `Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 < 8b0de7005b148738d79d6c45594d566489948a68`
- `Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 < 2b9a07002c2f296aa6a9c591213933d3492e3089`
- `Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 < 2fa11c60c9c06bafc19cf4d9efdaa36a38079e87`
- `Linux >= bc70fbf269fdff410b0b6d75c3770b9f59117b90 < 83abe2fd5b3aeb3123b5408a5a91709c5538fb23`
- `Linux 5.19`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.