CVE-2026-89927

/// Technical description

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

KVM: x86: hyper-v: Clamp stimer deadline to avoid livelock

Fix an issue where userspace or the guest can program an Hyper-V

synthetic timer to have a deadline in the past via integer overflow,

preventing the CPU from making progress and triggering an RCU stall.

Hyper-V's SynIC exposes 4 per-vCPU synthetic timers to the

guest, which are emulated by KVM. Each is programmed through the

HV_X64_MSR_STIMERi_CONFIG and HV_X64_MSR_STIMERi_COUNT MSRs. Depending

on CONFIG, COUNT represents either the absolute expiration time or the

period of a periodic timer, both expressed in 100ns ticks. These timers

may be set both by the guest (WRMSR) and the host (KVM_SET_MSRS).

When the timer is enabled, stimer_start() translates COUNT to an

absolute monotonic deadline and arms an hrtimer. If COUNT is set to a

value close to U64_MAX, the deadline calculation can overflow.

ktime_add_ns(ktime_now, 100 * (stimer->exp_time - time_now)

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References