{ "affected": [ { "ranges": [ { "events": [ { "introduced": "1f4b34f825e8cef6f493d06b46605384785b3d16" }, { "fixed": "a4665762388750e08df99baabe5fce2a21d1423e" }, { "fixed": "61954727ee08f026f5e1c9ee69e1b404a68f2f7a" }, { "fixed": "8aa467fe757d8cb2278e98d7fbf44fc05eb0dbf8" }, { "fixed": "8e19ded84336891646b31375720717635f0fdd90" }, { "fixed": "6a8ba9213cce613455b1502ee0fd178656bf617b" }, { "fixed": "3097582b73a8ed1cd6f6790fa78706f4a79b5a49" }, { "fixed": "bdb732ebee545b7e3bee7060efc754a8d99818b9" }, { "fixed": "0ca49fbd2883cd53d32d85b50feef17fa04d0fbf" } ], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "type": "GIT" } ] }, { "package": { "ecosystem": "Linux", "name": "Kernel" }, "ranges": [ { "events": [ { "introduced": "4.5.0" }, { "fixed": "5.10.270" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "5.11.0" }, { "fixed": "5.15.221" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "5.16.0" }, { "fixed": "6.1.188" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.2.0" }, { "fixed": "6.6.157" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.7.0" }, { "fixed": "6.12.110" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.13.0" }, { "fixed": "6.18.51" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.19.0" }, { "fixed": "7.2.5" } ], "type": "ECOSYSTEM" } ] } ], "database_specific": { "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89927.json" }, "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: hyper-v: Clamp stimer deadline to avoid livelock\n\nFix an issue where userspace or the guest can program an Hyper-V\nsynthetic timer to have a deadline in the past via integer overflow,\npreventing the CPU from making progress and triggering an RCU stall.\n\nHyper-V's SynIC exposes 4 per-vCPU synthetic timers to the\nguest, which are emulated by KVM. Each is programmed through the\nHV_X64_MSR_STIMERi_CONFIG and HV_X64_MSR_STIMERi_COUNT MSRs. Depending\non CONFIG, COUNT represents either the absolute expiration time or the\nperiod of a periodic timer, both expressed in 100ns ticks. These timers\nmay be set both by the guest (WRMSR) and the host (KVM_SET_MSRS).\n\nWhen the timer is enabled, stimer_start() translates COUNT to an\nabsolute monotonic deadline and arms an hrtimer. If COUNT is set to a\nvalue close to U64_MAX, the deadline calculation can overflow.\n\n ktime_add_ns(ktime_now, 100 * (stimer-\u003eexp_time - time_now))\n\nThis can result in a CPU livelock. stimer_start() arms the timer\nvia hrtimer_start() with a deadline in the past, which causes it to\nimmediately fire. The stimer callback then raises KVM_RQ_HV_STIMER, with\nthe intention of causing KVM to deliver a synthetic interrupt on the\nnext vCPU guest enter.\n\nThen, once userspace issues KVM_RUN, vcpu_enter_guest() consumes the\nrequest, calling kvm_hv_process_stimers(). This would normally disable\nthe timer via stimer_expiration() once the deadline is in the past.\nHowever, the deadline comparison is done between the KVM reference\ncounter and stime-\u003eexp_time, which is a big value close to U64_MAX, so\nthis never happens for a few thousand years.\n\nkvm_hv_process_timers() then re-arms the timer via stimer_start(), since\nit was not disabled, which again fires immediately. Before entering\nthe guest, kvm_vcpu_exit_request() checks kvm_request_pending(),\nwhich returns true due to the newly raised KVM_REQ_HV_STIMER. Then\nvcpu_enter_guest() aborts the guest entry, returning early into\nvcpu_run(), which loops back again into vcpu_enter_guest(), restarting\nthe cycle.\n\nSince there are no manual yields in this loop, a task with SCHED_FIFO\nmay starve RCU grace-period kthreads, which exposes the stalls found\nby syzcaller:\n\n rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:\n rcu: (detected by 1, t=10502 jiffies, g=14269, q=1142 ncpus=2)\n rcu: All QSes seen, last rcu_preempt kthread activity 10500 (4294965239-4294954739), jiffies_till_next_fqs=1, root -\u003eqsmask 0x0\n rcu: rcu_preempt kthread starved for 10500 jiffies! g14269 f0x2 RCU_GP_WAIT_FQS(5) -\u003estate=0x0 -\u003ecpu=0\n rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.\n ( ... )\n Call Trace:\n \u003cIRQ\u003e\n __run_hrtimer kernel/time/hrtimer.c:1773 [inline]\n __hrtimer_run_queues+0x408/0xc30 kernel/time/hrtimer.c:1841\n hrtimer_interrupt+0x45b/0xaa0 kernel/time/hrtimer.c:1903\n local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1045 [inline]\n __sysvec_apic_timer_interrupt+0x102/0x3e0 arch/x86/kernel/apic/apic.c:1062\n instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]\n sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1056\n \u003c/IRQ\u003e\n \u003cTASK\u003e\n asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697\n RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]\n RIP: 0010:_raw_spin_unlock_irqrestore+0xa8/0x110 kernel/locking/spinlock.c:194\n 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 \u003ce8\u003e 23 6b 27 f6 65 8b 05 7c 60 5a 07 85 c0 74 40 48 c7 04 24 0e 36\n RSP: 0018:ffffc900040a7320 EFLAGS: 00000206\n RAX: 5de15cb931505900 RBX: 0000000000000a06 RCX: 5de15cb931505900\n RDX: 0000000000000007 RSI: ffffffff8daa9dc3 RDI: 0000000000000001\n RBP: ffffc900040a73b0 R08: ffffffff8fc3d0\n---truncated---", "id": "CVE-2026-89927", "modified": "2026-09-18T03:30:24.662804384Z", "published": "2026-09-16T10:32:19.473Z", "references": [ { "type": "WEB", "url": "https://git.kernel.org/stable/c/0ca49fbd2883cd53d32d85b50feef17fa04d0fbf" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/3097582b73a8ed1cd6f6790fa78706f4a79b5a49" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/61954727ee08f026f5e1c9ee69e1b404a68f2f7a" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/6a8ba9213cce613455b1502ee0fd178656bf617b" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/8aa467fe757d8cb2278e98d7fbf44fc05eb0dbf8" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/8e19ded84336891646b31375720717635f0fdd90" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/a4665762388750e08df99baabe5fce2a21d1423e" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/bdb732ebee545b7e3bee7060efc754a8d99818b9" }, { "type": "ADVISORY", "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89927.json" }, { "type": "ADVISORY", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89927" }, { "type": "PACKAGE", "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git" } ], "schema_version": "1.9.0", "severity": [ { "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H", "type": "CVSS_V3" } ], "summary": "KVM: x86: hyper-v: Clamp stimer deadline to avoid livelock" }