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KVM: x86: Fix VM hard lockup after prolonged inactivity with periodic HV timer

Linux kernel · CVE-2025-71104
0 news outlets0 CERTs and agencies0 researchers

What is it?

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Fix VM hard lockup after prolonged inactivity with periodic HV timer When advancing the target expiration for the guest's APIC timer in periodic mode, set the expiration to "now" if the target expiration is in the past (similar to what is done in update_target_expiration()). Blindly adding the period to the previous target expiration can result in KVM generating a practically unbounded number of hrtimer IRQs due to programming an expired timer over and over. In extreme scenarios, e.g. if userspace pauses/suspends a VM for an extended duration, this can even cause hard lockups in the host. Currently, the bug only affects Intel CPUs when using the hypervisor timer (HV timer), a.k.a. the VMX preemption timer. Unlike the software timer, a.k.a. hrtimer, which KVM keeps running even on exits to userspace, the HV timer only runs while the guest is active. As a result, if the vCPU does not run for an extended duration, there will be a huge gap between the target expiration and the current time the vCPU resumes running. Because the target expiration is incremented by only one period on each timer expiration

Evidence

No coverage recorded yet.

Exploitation

  • Public proof of concept
  • Exploited in the wild
  • Listed as known exploited
CVSS
Not scored
EPSS
0.1%
First seen
7 h ago
Status
corroborated

All Linux vulnerabilities