# CVE-2026-72043: LoongArch: Fix missing dirty page tracking in {pte,pmd}_wrprotect()


- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-72043, DEBIAN-CVE-2026-72043, GHSA-f7xg-fgxp-p6w3, UBUNTU-CVE-2026-72043

## What is CVE-2026-72043?

CVE-2026-72043 is a high-severity vulnerability in Linux, published on 15 Aug 2026. 

### Official description

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

LoongArch: Fix missing dirty page tracking in {pte,pmd}_wrprotect()

When hardware page table walker (PTW) is enabled on LoongArch, the CPU
may set _PAGE_DIRTY directly in the page table entry during a write TLB
miss, without going through the software TLB store handler. The software
TLB store handler (tlbex.S:254) sets both _PAGE_DIRTY and_PAGE_MODIFIED
together:

    ori t0, t0, (_PAGE_VALID | _PAGE_DIRTY | _PAGE_MODIFIED)

Since hardware PTW only sets _PAGE_DIRTY, the software-only bit, i.e.
_PAGE_MODIFIED is left unchanged. This creates a window where a PTE has
_PAGE_DIRTY set (hardware knows the page is dirty) but _PAGE_MODIFIED
clear (software is unaware).

When fork()/clone() triggers copy-on-write, __copy_present_ptes() calls
pte_wrprotect(), which unconditionally clears both the _PAGE_WRITE and
_PAGE_DIRTY bits:

    pte_val(pte) &= ~(_PAGE_WRITE | _PAGE_DIRTY);

Since _PAGE_MODIFIED was never set, the dirtiness information is lost
completely. Subsequently, when memory pressure triggers page reclaim,
page_mkclean() / try_to_unmap() sees the page as clean (i.e. pte_dirty()
returns false) and the page may be freed without writeback, causing data
corruption.

Fix this by propagating the _PAGE_DIRTY bit to the _PAGE_MODIFIED bit in
both pte_wrprotect() and pmd_wrprotect() before clearing writeable bits:

    if (pte_val(pte) & _PAGE_DIRTY)
        pte_val(pte) |= _PAGE_MODIFIED;

The pmd_wrprotect() fix handles the CONFIG_TRANSPARENT_HUGEPAGE case,
where pmd entries need the same treatment.

This ensures the software dirty tracking bit (checked by pte_dirty() and
pmd_dirty(), which read both the _PAGE_DIRTY and _PAGE_MODIFIED bits) is
preserved across fork COW write-protection.

The issue was found by the LTP madvise09 test case, which exercises page
reclaim after "madvise(MADV_FREE), write and fork" operation sequence on
private anonymous mappings.

## Which versions are affected by CVE-2026-72043?


## How do I fix CVE-2026-72043?

Upgrade to a fixed version.

## Is CVE-2026-72043 being exploited?

There is no known exploitation of CVE-2026-72043 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72043 and fix it if it is affected.

What it is: CVE-2026-72043 is a high-severity vulnerability in Linux, published on 15 Aug 2026. 
Exploitation: There is no known exploitation of CVE-2026-72043 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72043/ (Markdown: https://insights.sbomify.com/CVE-2026-72043/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72043
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72043
- OSV: https://osv.dev/vulnerability/CVE-2026-72043

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72043/
Summaries are generated and may contain mistakes; the official description above is the record.