# CVE-2020-8834: Linux kernel KVM Power8 conflicting use of HSTATE_HOST_R1

> A guest VM attacker can trigger a host kernel panic via a race condition in KVM Power8 transactional memory state handling.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/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:** 9 Apr 2020
- **Updated:** 16 Sep 2024
- **Also known as:** DEBIAN-CVE-2020-8834, GHSA-7fx7-755p-qmjj, UBUNTU-CVE-2020-8834

## What is CVE-2020-8834?

CVE-2020-8834 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 9 Apr 2020. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

KVM in the Linux kernel on Power8 processors has a conflicting use of HSTATE_HOST_R1 to store r1 state in kvmppc_hv_entry plus in kvmppc_{save,restore}_tm, leading to a stack corruption. Because of this, an attacker with the ability run code in kernel space of a guest VM can cause the host kernel to panic. There were two commits that, according to the reporter, introduced the vulnerability: f024ee098476 ("KVM: PPC: Book3S HV: Pull out TM state save/restore into separate procedures") 87a11bb6a7f7 ("KVM: PPC: Book3S HV: Work around XER[SO] bug in fake suspend mode") The former landed in 4.8, the latter in 4.17. This was fixed without realizing the impact in 4.18 with the following three commits, though it's believed the first is the only strictly necessary commit: 6f597c6b63b6 ("KVM: PPC: Book3S PR: Add guest MSR parameter for kvmppc_save_tm()/kvmppc_restore_tm()") 7b0e827c6970 ("KVM: PPC: Book3S HV: Factor fake-suspend handling out of kvmppc_save/restore_tm") 009c872a8bc4 ("KVM: PPC: Book3S PR: Move kvmppc_save_tm/kvmppc_restore_tm to separate file")

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization), CWE-368 (Context Switching Race Condition)

## Which versions are affected by CVE-2020-8834?

It affects 3 products.


Products: Canonical Ubuntu Linux, Linux kernel, Opensuse Leap.

## How do I fix CVE-2020-8834?

Apply the vendor's patch.

## Is CVE-2020-8834 being exploited?

There is no known exploitation of CVE-2020-8834 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-8834 and fix it if it is affected.

What it is: CVE-2020-8834 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 9 Apr 2020. 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-2020-8834 in the wild and no public exploit code.

Affected product: Canonical Ubuntu 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-2020-8834/ (Markdown: https://insights.sbomify.com/CVE-2020-8834/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-8834
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-8834
- OSV: https://osv.dev/vulnerability/CVE-2020-8834

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-8834/
Summaries are generated and may contain mistakes; the official description above is the record.