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CVE-2026-89927— KVM: x86: hyper-v: Clamp stimer deadline to avoid livelock

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

以下是该漏洞描述的中文翻译： 在 Linux 内核中，以下漏洞已得到修复： KVM: x86: hyper-v: 将 stimer 截止时间钳位以避免活锁（Livelock） 修复了用户空间或客户机通过整数溢出将 Hyper-V 合成定时器（synthetic timer）编程为具有“过去”截止时间的问题，该问题会导致 CPU 无法取得进展并触发 RCU 卡顿。 Hyper-V 的 SynIC 向客户机暴露了 4 个每 vCPU 的合成定时器，这些定时器由 KVM 进行仿真。每个定时器通过 和 MSR 进行编程。根

CVSS 7.1 · High EPSS 0.19% · P8

Possible ATT&CK Techniques 1 AI

T1022

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 1f4b34f825e8cef6f493d06b46605384785b3d16< a4665762388750e08df99baabe5fce2a21d1423e affected
1f4b34f825e8cef6f493d06b46605384785b3d16< 61954727ee08f026f5e1c9ee69e1b404a68f2f7a affected
1f4b34f825e8cef6f493d06b46605384785b3d16< 8aa467fe757d8cb2278e98d7fbf44fc05eb0dbf8 affected
1f4b34f825e8cef6f493d06b46605384785b3d16< 8e19ded84336891646b31375720717635f0fdd90 affected
1f4b34f825e8cef6f493d06b46605384785b3d16< 6a8ba9213cce613455b1502ee0fd178656bf617b affected
1f4b34f825e8cef6f493d06b46605384785b3d16< 3097582b73a8ed1cd6f6790fa78706f4a79b5a49 affected
1f4b34f825e8cef6f493d06b46605384785b3d16< bdb732ebee545b7e3bee7060efc754a8d99818b9 affected
1f4b34f825e8cef6f493d06b46605384785b3d16< 0ca49fbd2883cd53d32d85b50feef17fa04d0fbf affected
… +10 more rows
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I. Basic Information for CVE-2026-89927

Vulnerability Information
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Vulnerability Title
KVM: x86: hyper-v: Clamp stimer deadline to avoid livelock
Source: CVE Program / CVE List V5
Vulnerability 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)) This can result in a CPU livelock. stimer_start() arms the timer via hrtimer_start() with a deadline in the past, which causes it to immediately fire. The stimer callback then raises KVM_RQ_HV_STIMER, with the intention of causing KVM to deliver a synthetic interrupt on the next vCPU guest enter. Then, once userspace issues KVM_RUN, vcpu_enter_guest() consumes the request, calling kvm_hv_process_stimers(). This would normally disable the timer via stimer_expiration() once the deadline is in the past. However, the deadline comparison is done between the KVM reference counter and stime->exp_time, which is a big value close to U64_MAX, so this never happens for a few thousand years. kvm_hv_process_timers() then re-arms the timer via stimer_start(), since it was not disabled, which again fires immediately. Before entering the guest, kvm_vcpu_exit_request() checks kvm_request_pending(), which returns true due to the newly raised KVM_REQ_HV_STIMER. Then vcpu_enter_guest() aborts the guest entry, returning early into vcpu_run(), which loops back again into vcpu_enter_guest(), restarting the cycle. Since there are no manual yields in this loop, a task with SCHED_FIFO may starve RCU grace-period kthreads, which exposes the stalls found by syzcaller: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: (detected by 1, t=10502 jiffies, g=14269, q=1142 ncpus=2) rcu: All QSes seen, last rcu_preempt kthread activity 10500 (4294965239-4294954739), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread starved for 10500 jiffies! g14269 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0 rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior. ( ... ) Call Trace: <IRQ> __run_hrtimer kernel/time/hrtimer.c:1773 [inline] __hrtimer_run_queues+0x408/0xc30 kernel/time/hrtimer.c:1841 hrtimer_interrupt+0x45b/0xaa0 kernel/time/hrtimer.c:1903 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1045 [inline] __sysvec_apic_timer_interrupt+0x102/0x3e0 arch/x86/kernel/apic/apic.c:1062 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline] sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1056 </IRQ> <TASK> asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697 RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline] RIP: 0010:_raw_spin_unlock_irqrestore+0xa8/0x110 kernel/locking/spinlock.c:194 Code: 74 05 e8 0b f4 5f f6 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4f f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 23 6b 27 f6 65 8b 05 7c 60 5a 07 85 c0 74 40 48 c7 04 24 0e 36 RSP: 0018:ffffc900040a7320 EFLAGS: 00000206 RAX: 5de15cb931505900 RBX: 0000000000000a06 RCX: 5de15cb931505900 RDX: 0000000000000007 RSI: ffffffff8daa9dc3 RDI: 0000000000000001 RBP: ffffc900040a73b0 R08: ffffffff8fc3d0 ---truncated---
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 1f4b34f825e8cef6f493d06b46605384785b3d16 ~ a4665762388750e08df99baabe5fce2a21d1423e -
Linux Linux 4.5 -

II. Public POCs for CVE-2026-89927

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III. Intelligence Information for CVE-2026-89927

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Other References for CVE-2026-89927 (8)

Same Patch Batch · Linux · 2026-09-16 · 276 CVEs total

CVE-2026-90048 9.8 CRITICAL fs/ntfs3: fix slab-out-of-bounds write in ni_create_attr_list()
CVE-2026-90012 9.8 CRITICAL spi: Fix DMA mapping ownership on partial map failure
CVE-2026-89970 9.8 CRITICAL nvmet-auth: Synchronize timeout work during SQ teardown
CVE-2026-89857 9.8 CRITICAL scsi: qla2xxx: Hold qpair lock when sending NVMe LS reject
CVE-2026-89969 9.8 CRITICAL nvmet-tcp: fix out-of-bounds write when receiving an over-long PDU
CVE-2026-89847 9.8 CRITICAL scsi: qla2xxx: Avoid double completion in async IOCB timeout
CVE-2026-89972 9.8 CRITICAL nvme: add missing SRCU grace period in error path
CVE-2026-89990 9.8 CRITICAL ceph: lock mutex in ceph_mds_check_access()
CVE-2026-90036 9.8 CRITICAL NFSD: Prevent client use-after-free during blocked-lock reaping
CVE-2026-90038 9.8 CRITICAL NFSD: Prevent client use-after-free during export state revocation
CVE-2026-90037 9.8 CRITICAL NFSD: Prevent client use-after-free during close_lru reaping
CVE-2026-89788 9.8 CRITICAL ksmbd: fix tree connection use-after-free in smb2_tree_connect()
CVE-2026-89783 9.8 CRITICAL xfrm6: fix out-of-bounds write in xfrm6_input_addr() when secpath is full
CVE-2026-90042 9.8 CRITICAL ceph: properly decrypt filenames in vmalloc() buffers
CVE-2026-89778 9.8 CRITICAL isofs: fix out-of-bounds page array access on empty zisofs block
CVE-2026-89915 9.3 CRITICAL KVM: arm64: Remove VM-wide VNCR mapping counter
CVE-2026-90049 9.3 CRITICAL net: skbuff: don't skb_tx_error() the source skb in skb_zerocopy()
CVE-2026-89775 9.3 CRITICAL KVM: arm64: Handle negative S1 walk levels in VNCR TLB size evaluation
CVE-2026-89916 9.3 CRITICAL KVM: arm64: Make VNCR invalidation participate in MMU invalidation retry
CVE-2026-89930 9.3 CRITICAL KVM: nVMX: Service local TLB flushes on failed nested VM-Enter

Showing top 20 of 276 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

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