GHSA-W23M-4J94-2GWQ
Vulnerability from github – Published: 2026-10-18 18:31 – Updated: 2026-10-24 15:32In 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.
{
"affected": [],
"aliases": [
"CVE-2026-98464"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-18T16:16:56Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nRISC-V: KVM: Synchronize hrtimer callback during teardown\n\nThe non-Sstc hrtimer callback clears next_set before its final uses of\nthe enclosing vCPU. If teardown observes next_set as false while the\ncallback is still running, kvm_riscv_vcpu_timer_cancel() skips\nhrtimer_cancel() and kvm_destroy_vcpus() can free the vCPU before the\ncallback enters kvm_riscv_vcpu_set_interrupt().\n\nA guest can arm the timer with SBI TIME and request shutdown with SBI\nlegacy shutdown or SRST. A VMM that honors KVM_EXIT_SYSTEM_EVENT and\ndestroys the VM supplies the teardown side of the race; no post-launch\nhost ioctl is needed to arm or request teardown.\n\nOn upstream master 62cc90241548, generic KASAN reported:\n\n BUG: KASAN: slab-use-after-free in do_raw_spin_lock\n Write of size 4 at addr ff60000005e58898\n\n kvm_riscv_vcpu_set_interrupt\n kvm_riscv_vcpu_hrtimer_expired\n __hrtimer_run_queues\n hrtimer_interrupt\n\nThe object was allocated by KVM_CREATE_VCPU and freed concurrently by:\n\n kvm_destroy_vcpus\n kvm_arch_destroy_vm\n kvm_destroy_vm\n __fput\n\nFor deterministic validation, I added mdelay(1000) immediately after\nthe existing next_set = false assignment. This only widens the\nexisting post-clear callback window. A no-delay trace build naturally\nreached the callback-after-teardown-start/before-deinit ordering in 12\nof 200 runs, but 1,500 stock-kernel stress iterations did not produce a\nKASAN report, so natural reproduction is timing-sensitive.\n\nAlways invoke hrtimer_cancel() for an initialized timer. Preserve the\nexisting -EINVAL result when the timer is no longer set, but only after\nsynchronizing with a running callback.\n\nWith this patch, hrtimer_cancel() blocked for the full widened callback\nwindow before vCPU destruction. KASAN reported no error in 100\nfixed-and-widened runs or 200 fix-only timing-sweep runs.",
"id": "GHSA-w23m-4j94-2gwq",
"modified": "2026-10-24T15:32:46Z",
"published": "2026-10-18T18:31:49Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98464"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2af03b606aadaaeb386658ef798c79bdcdef87c1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3cc6184bd5920c9685d87f4e260568feba08650d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9bdbae64ae0dab93041ebc57ec4e93def793fc2d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/aaad136d56d91252517272b68cd533e5714698d5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e66aced74f0122380603c9910a71d77618b28f0e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ea91f05a55b807ead3166546a2c75f4185ca645f"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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