---
id: "CVE-2026-98464"
kind: "vulnerability"
aliases: ["CVE-2026-98464"]
title: "Linux KVM RISC-V: timer callback can use a freed vCPU during teardown"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "kvm", "linux-kernel", "riscv", "self-hosted"]
not_affected_if: ["kvm-not-used", "no-riscv-hosts"]
published_at: "2026-10-18T16:16:56+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:27:14+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98464", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux KVM RISC-V: timer callback can use a freed vCPU during teardown

In the RISC-V KVM timer code, a timer callback can run after the guest vCPU has been freed during VM shutdown, causing a use-after-free in the kernel. A guest that arms the SBI timer and requests shutdown can trigger the race when the VMM destroys the VM, and the sources do not state a confirmed attacker outcome beyond the memory corruption.

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

## How to check

- Check whether the host runs a Linux kernel with RISC-V KVM enabled (`CONFIG_KVM` on a riscv64 host).
- Compare the running kernel with the fixed upstream version: `uname -r`; the sources do not name a fixed version.
- Check whether a VMM runs RISC-V guests with KVM: unknown.

## Fix

- Update the Linux kernel to a release that includes the upstream fix (the sources do not name a version: unknown).
- Until patched, avoid running RISC-V KVM guests on untrusted workloads: unknown.

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98464

## From the sources

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

RISC-V: KVM: Synchronize hrtimer callback during teardown

The non-Sstc hrtimer callback clears next_set before its final uses of
the enclosing vCPU.  If teardown observes next_set as false while the
callback is still running, kvm_riscv_vcpu_timer_cancel() skips
hrtimer_cancel() and kvm_destroy_vcpus() can free the vCPU before the
callback enters kvm_riscv_vcpu_set_interrupt().

A guest can arm the timer with SBI TIME and request shutdown with SBI
legacy shutdown or SRST.  A VMM that honors KVM_EXIT_SYSTEM_EVENT and
destroys the VM supplies the teardown side of the race; no post-launch
host ioctl is needed to arm or request teardown.

On upstream master 62cc90241548, generic KASAN reported:

  BUG: KASAN: slab-use-after-free in do_raw_spin_lock
  Write of size 4 at addr ff60000005e58898

  kvm_riscv_vcpu_set_interrupt
  kvm_riscv_vcpu_hrtimer_expired
  __hrtimer_run_queues
  hrtimer_interrupt

The object was allocated by KVM_CREATE_VCPU and freed concurrently by:

  kvm_destroy_vcpus
  kvm_arch_destroy_vm
  kvm_destroy_vm
  __fput

For deterministic validation, I added mdelay(1000) immediately after
the existing next_set = false assignment.  This only widens the
existing post-clear callback window.  A no-delay trace build naturally
reached the callback-after-teardown-start/before-deinit ordering in 12
of 200 runs, but 1,500 stock-kernel stress iterations did not produce a
KASAN report, so natural reproduction is timing-sensitive.

Always invoke hrtimer_cancel() for an initialized timer.  Preserve the
existing -EINVAL result when the timer is no longer set, but only after
synchronizing with a running callback.

With this patch, hrtimer_cancel() blocked for the full widened callback
window before vCPU destruction.  KASAN reported no error in 100
fixed-and-widened runs or 200 fix-only timing-sweep runs.

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