# CVE-2026-89459: s390/percpu: Fix MVIY_PERCPU() with older binutils

> A build-time assembler bug on s390x with older binutils prevents proper per-CPU exception handling, potentially causing instability or crashes.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-mqmh-f84h-6j7h, UBUNTU-CVE-2026-89459

## What is CVE-2026-89459?

CVE-2026-89459 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

s390/percpu: Fix MVIY_PERCPU() with older binutils

Commit a737737cdb9c ("s390/percpu: Infrastructure for more efficient
this_cpu operations") introduced MVIY_PERCPU(), which stringifies
arguments that are already C string literals. This generates an
assembler macro invocation with whitespace-separated quoted arguments:

  GEN_MVIY "459712" "%r3"

GNU as versions prior to binutils 2.39 drop the separating whitespace
between quoted macro arguments during input scrubbing. They
consequently parse the invocation as a single argument and emit
repeated warnings:

  Warning: missing closing `"'

The .ifc in GEN_MVIY never matches and GNU as exits successfully
without emitting the mviy instruction. As a result, the interrupted
per-CPU sequence is not marked in lowcore and the exception return
path cannot repair the per-CPU address register after migration.

All MVIY_PERCPU() callers pass C string literals. Use them directly
and separate the assembler macro arguments with an explicit comma. The
resulting invocation is:

  GEN_MVIY 459712, %r3

This form is unambiguous for GNU as and LLVM's integrated assembler.
This behavior was fixed in GNU as from binutils 2.39, but Linux
supports binutils 2.30.

## Which versions are affected by CVE-2026-89459?


## How do I fix CVE-2026-89459?

Apply the vendor's patch.

## Is CVE-2026-89459 being exploited?

There is no known exploitation of CVE-2026-89459 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89459 and fix it if it is affected.

What it is: CVE-2026-89459 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89459 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-2026-89459/ (Markdown: https://insights.sbomify.com/CVE-2026-89459/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89459
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89459
- OSV: https://osv.dev/vulnerability/CVE-2026-89459

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89459/
Summaries are generated and may contain mistakes; the official description above is the record.