# CVE-2026-93259: powerpc/irq: Fix missing r2 clobber in PCREL inline assembly

> A missing register clobber in PowerPC kernel interrupt handling causes crashes and boot failures when PCREL mode is enabled.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-93259, DEBIAN-CVE-2026-93259, GHSA-8h7f-5wc3-64cf, UBUNTU-CVE-2026-93259

## What is CVE-2026-93259?

CVE-2026-93259 is a denial of service vulnerability in Linux, published on 24 Sep 2026. 

### Official description

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

powerpc/irq: Fix missing r2 clobber in PCREL inline assembly

In CONFIG_PPC_KERNEL_PCREL mode, r2 is no longer reserved for the TOC
pointer and is available as a caller-saved register [0].

Both call_do_irq() and call_do_softirq() use inline assembly to call
functions with stack switching, but fail to list r2 in their clobber
lists. This causes the compiler to assume r2 is preserved across these
calls, leading to register corruption when the called functions
(__do_irq and __do_softirq) clobber r2.

As a result of this kernel crash during interrupt handling is seen and
the kernel fails to boot:

BUG: Unable to handle kernel data access on write at 0xc000000404697638
Faulting instruction address: 0xc0000000000181ec
Oops: Kernel access of bad area, sig: 11 [#1]
NIP [c0000000000181ec] __do_IRQ+0x6c/0xc0

With older GCC, the compiler would conservatively allocate
callee-saved registers (like r31) for values spanning function calls,
accidentally avoiding the bug:

<__do_IRQ>:
00 00 00 60 	nop
a6 02 08 7c 	mflr    r0
f8 ff e1 fb 	std     r31,-8(r1)
f0 ff c1 fb 	std     r30,-16(r1)
2d 03 10 06 	pla     r31,53297316

...

3d e8 ff 4b 	bl      c0000000000165ac <__do_irq>
00 00 21 e8 	ld      r1,0(r1)
28 00 4d e9 	ld      r10,40(r13)
40 00 21 38 	addi    r1,r1,64
2a f9 aa 7f 	stdx    r29,r10,r31

With newer GCC 14, the compiler uses r2 for such values, exposing the
missing clobber specification:

<__do_IRQ>:
00 00 00 60     nop
a6 02 08 7c     mflr    r0
f0 ff c1 fb     std     r30,-16(r1)
f8 ff e1 fb     std     r31,-8(r1)
29 02 10 06     pla     r2,36252592     # c0000000022aadc0 <__irq_regs>

...

85 dc ff 4b 	bl      c000000000015ee0 <__do_irq>
00 00 21 e8 	ld      r1,0(r1)
28 00 2d e9 	ld      r9,40(r13)
30 00 21 38 	addi    r1,r1,48
2a 11 c9 7f 	stdx    r30,r9,r2

Fix this by adding r2 to the clobber list for both call_do_irq() and
call_do_softirq() when CONFIG_PPC_KERNEL_PCREL is enabled.

[0]: https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg313226.html

## Which versions are affected by CVE-2026-93259?


## How do I fix CVE-2026-93259?

Apply the vendor's patch.

## Is CVE-2026-93259 being exploited?

There is no known exploitation of CVE-2026-93259 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93259 and fix it if it is affected.

What it is: CVE-2026-93259 is a denial of service vulnerability in Linux, published on 24 Sep 2026. 
Exploitation: There is no known exploitation of CVE-2026-93259 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-2026-93259/ (Markdown: https://insights.sbomify.com/CVE-2026-93259/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93259
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93259
- OSV: https://osv.dev/vulnerability/CVE-2026-93259

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93259/
Summaries are generated and may contain mistakes; the official description above is the record.