---
id: "CVE-2026-98638"
kind: "vulnerability"
aliases: ["CVE-2026-98638"]
title: "Linux kernel KVM arm64: invalid SVE vector length can crash the hypervisor"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["arm64", "infrastructure", "kvm", "linux-kernel", "pkvm"]
not_affected_if: ["non-arm64-hardware", "pkvm-not-enabled"]
published_at: "2026-10-18T16:17:16+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:20:57+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98638", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux kernel KVM arm64: invalid SVE vector length can crash the hypervisor

In the Linux kernel's arm64 KVM, pkvm_vcpu_init_sve() checks only the upper bound of the host-provided SVE vector length, so an invalid length reaches a WARN_ON() that is fatal at EL2. The sources do not state what an attacker can do beyond triggering that failure.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- unknown

## Fix

- Apply the kernel fix that validates the SVE vector length with sve_vl_valid() before deriving the state size in pkvm_vcpu_init_sve(); the sources do not name fixed kernel versions.

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98638

## From the sources

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

KVM: arm64: Validate the SVE vector length in pkvm_vcpu_init_sve()

pkvm_vcpu_init_sve() clamps only the upper bound of the host-provided
sve_max_vl, so an invalid vector length reaches sve_state_size_from_vl()
and the WARN_ON() there, which is fatal at EL2. The existing
!sve_state_size test rejects such a length, but only after the macro has
run.

Check sve_vl_valid() before deriving the state size. A valid length
cannot yield a zero size, so the !sve_state_size test goes with it.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_