CVE-2024-26976 (GCVE-0-2024-26976)
Vulnerability from cvelistv5 – Published: 2024-05-01 05:20 – Updated: 2026-08-05 11:28
VLAI
EPSS
VEX
Title
KVM: Always flush async #PF workqueue when vCPU is being destroyed
Summary
In the Linux kernel, the following vulnerability has been resolved:
KVM: Always flush async #PF workqueue when vCPU is being destroyed
Always flush the per-vCPU async #PF workqueue when a vCPU is clearing its
completion queue, e.g. when a VM and all its vCPUs is being destroyed.
KVM must ensure that none of its workqueue callbacks is running when the
last reference to the KVM _module_ is put. Gifting a reference to the
associated VM prevents the workqueue callback from dereferencing freed
vCPU/VM memory, but does not prevent the KVM module from being unloaded
before the callback completes.
Drop the misguided VM refcount gifting, as calling kvm_put_kvm() from
async_pf_execute() if kvm_put_kvm() flushes the async #PF workqueue will
result in deadlock. async_pf_execute() can't return until kvm_put_kvm()
finishes, and kvm_put_kvm() can't return until async_pf_execute() finishes:
WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+0x2d/0x320 [kvm]
Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass
CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Workqueue: events async_pf_execute [kvm]
RIP: 0010:kvm_put_kvm+0x2d/0x320 [kvm]
Call Trace:
<TASK>
async_pf_execute+0x198/0x260 [kvm]
process_one_work+0x145/0x2d0
worker_thread+0x27e/0x3a0
kthread+0xba/0xe0
ret_from_fork+0x2d/0x50
ret_from_fork_asm+0x11/0x20
</TASK>
---[ end trace 0000000000000000 ]---
INFO: task kworker/8:1:251 blocked for more than 120 seconds.
Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/8:1 state:D stack:0 pid:251 ppid:2 flags:0x00004000
Workqueue: events async_pf_execute [kvm]
Call Trace:
<TASK>
__schedule+0x33f/0xa40
schedule+0x53/0xc0
schedule_timeout+0x12a/0x140
__wait_for_common+0x8d/0x1d0
__flush_work.isra.0+0x19f/0x2c0
kvm_clear_async_pf_completion_queue+0x129/0x190 [kvm]
kvm_arch_destroy_vm+0x78/0x1b0 [kvm]
kvm_put_kvm+0x1c1/0x320 [kvm]
async_pf_execute+0x198/0x260 [kvm]
process_one_work+0x145/0x2d0
worker_thread+0x27e/0x3a0
kthread+0xba/0xe0
ret_from_fork+0x2d/0x50
ret_from_fork_asm+0x11/0x20
</TASK>
If kvm_clear_async_pf_completion_queue() actually flushes the workqueue,
then there's no need to gift async_pf_execute() a reference because all
invocations of async_pf_execute() will be forced to complete before the
vCPU and its VM are destroyed/freed. And that in turn fixes the module
unloading bug as __fput() won't do module_put() on the last vCPU reference
until the vCPU has been freed, e.g. if closing the vCPU file also puts the
last reference to the KVM module.
Note that kvm_check_async_pf_completion() may also take the work item off
the completion queue and so also needs to flush the work queue, as the
work will not be seen by kvm_clear_async_pf_completion_queue(). Waiting
on the workqueue could theoretically delay a vCPU due to waiting for the
work to complete, but that's a very, very small chance, and likely a very
small delay. kvm_arch_async_page_present_queued() unconditionally makes a
new request, i.e. will effectively delay entering the guest, so the
remaining work is really just:
trace_kvm_async_pf_completed(addr, cr2_or_gpa);
__kvm_vcpu_wake_up(vcpu);
mmput(mm);
and mmput() can't drop the last reference to the page tables if the vCPU is
still alive, i.e. the vCPU won't get stuck tearing down page tables.
Add a helper to do the flushing, specifically to deal with "wakeup all"
work items, as they aren't actually work items, i.e. are never placed in a
workqueue. Trying to flush a bogus workqueue entry rightly makes
__flush_work() complain (kudos to whoever added that sanity check).
Note, commit 5f6de5cbebee ("KVM: Prevent module exit until al
---truncated---
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-02-05 21:06 UTC
CWE
- CWE-400 - Uncontrolled Resource Consumption
Assigner
References
11 references
Impacted products
22 products
| Vendor | Product | Version | |
|---|---|---|---|
| Linux | Linux |
Affected:
af585b921e5d1e919947c4b1164b59507fe7cd7b , < ab2c2f5d9576112ad22cfd3798071cb74693b1f5
(git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 82e25cc1c2e93c3023da98be282322fc08b61ffb (git) Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < f8730d6335e5f43d09151fca1f0f41922209a264 (git) Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 83d3c5e309611ef593e2fcb78444fc8ceedf9bac (git) Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < b54478d20375874aeee257744dedfd3e413432ff (git) Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < a75afe480d4349c524d9c659b1a5a544dbc39a98 (git) Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 4f3a3bce428fb439c66a578adc447afce7b4a750 (git) Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < caa9af2e27c275e089d702cfbaaece3b42bca31b (git) Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 3d75b8aa5c29058a512db29da7cbee8052724157 (git) |
|
| Linux | Linux |
Affected:
2.6.38
Unaffected: 0 , < 2.6.38 (semver) Unaffected: 4.19.312 , ≤ 4.19.* (semver) Unaffected: 5.4.274 , ≤ 5.4.* (semver) Unaffected: 5.10.215 , ≤ 5.10.* (semver) Unaffected: 5.15.154 , ≤ 5.15.* (semver) Unaffected: 6.1.84 , ≤ 6.1.* (semver) Unaffected: 6.6.24 , ≤ 6.6.* (semver) Unaffected: 6.7.12 , ≤ 6.7.* (semver) Unaffected: 6.8.3 , ≤ 6.8.* (semver) Unaffected: 6.9 , ≤ * (original_commit_for_fix) |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < ab2c2f5d9576
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < 82e25cc1c2e9
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < 8730d6335e5
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < 83d3c5e30961
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < b54478d20375
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < a75afe480d43
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < 4f3a3bce428f
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < caa9af2e27c2
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
af585b921e5d , < 3d75b8aa5c29
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Affected:
2.6.38
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
0 , < 2.6.38
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
4.19.312 , ≤ 4.20
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
5.4.274 , ≤ 5.5
(custom)
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
5.10.215 , ≤ 5.11
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
5.15.154 , ≤ 5.16
(custom)
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
6.1.84 , ≤ 6.2
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
6.6.24 , ≤ 6.7
(custom)
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
6.7.12 , ≤ 6.8
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
6.8.3 , ≤ 6.9
(custom)
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
|
| linux | linux_kernel |
Unaffected:
6.9
cpe:2.3:o:linux:linux_kernel:-:*:*:*:*:*:*:* |
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Always flush async #PF workqueue when vCPU is being destroyed\n\nAlways flush the per-vCPU async #PF workqueue when a vCPU is clearing its\ncompletion queue, e.g. when a VM and all its vCPUs is being destroyed.\nKVM must ensure that none of its workqueue callbacks is running when the\nlast reference to the KVM _module_ is put. Gifting a reference to the\nassociated VM prevents the workqueue callback from dereferencing freed\nvCPU/VM memory, but does not prevent the KVM module from being unloaded\nbefore the callback completes.\n\nDrop the misguided VM refcount gifting, as calling kvm_put_kvm() from\nasync_pf_execute() if kvm_put_kvm() flushes the async #PF workqueue will\nresult in deadlock. async_pf_execute() can\u0027t return until kvm_put_kvm()\nfinishes, and kvm_put_kvm() can\u0027t return until async_pf_execute() finishes:\n\n WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+0x2d/0x320 [kvm]\n Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass\n CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n Workqueue: events async_pf_execute [kvm]\n RIP: 0010:kvm_put_kvm+0x2d/0x320 [kvm]\n Call Trace:\n \u003cTASK\u003e\n async_pf_execute+0x198/0x260 [kvm]\n process_one_work+0x145/0x2d0\n worker_thread+0x27e/0x3a0\n kthread+0xba/0xe0\n ret_from_fork+0x2d/0x50\n ret_from_fork_asm+0x11/0x20\n \u003c/TASK\u003e\n ---[ end trace 0000000000000000 ]---\n INFO: task kworker/8:1:251 blocked for more than 120 seconds.\n Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\n \"echo 0 \u003e /proc/sys/kernel/hung_task_timeout_secs\" disables this message.\n task:kworker/8:1 state:D stack:0 pid:251 ppid:2 flags:0x00004000\n Workqueue: events async_pf_execute [kvm]\n Call Trace:\n \u003cTASK\u003e\n __schedule+0x33f/0xa40\n schedule+0x53/0xc0\n schedule_timeout+0x12a/0x140\n __wait_for_common+0x8d/0x1d0\n __flush_work.isra.0+0x19f/0x2c0\n kvm_clear_async_pf_completion_queue+0x129/0x190 [kvm]\n kvm_arch_destroy_vm+0x78/0x1b0 [kvm]\n kvm_put_kvm+0x1c1/0x320 [kvm]\n async_pf_execute+0x198/0x260 [kvm]\n process_one_work+0x145/0x2d0\n worker_thread+0x27e/0x3a0\n kthread+0xba/0xe0\n ret_from_fork+0x2d/0x50\n ret_from_fork_asm+0x11/0x20\n \u003c/TASK\u003e\n\nIf kvm_clear_async_pf_completion_queue() actually flushes the workqueue,\nthen there\u0027s no need to gift async_pf_execute() a reference because all\ninvocations of async_pf_execute() will be forced to complete before the\nvCPU and its VM are destroyed/freed. And that in turn fixes the module\nunloading bug as __fput() won\u0027t do module_put() on the last vCPU reference\nuntil the vCPU has been freed, e.g. if closing the vCPU file also puts the\nlast reference to the KVM module.\n\nNote that kvm_check_async_pf_completion() may also take the work item off\nthe completion queue and so also needs to flush the work queue, as the\nwork will not be seen by kvm_clear_async_pf_completion_queue(). Waiting\non the workqueue could theoretically delay a vCPU due to waiting for the\nwork to complete, but that\u0027s a very, very small chance, and likely a very\nsmall delay. kvm_arch_async_page_present_queued() unconditionally makes a\nnew request, i.e. will effectively delay entering the guest, so the\nremaining work is really just:\n\n trace_kvm_async_pf_completed(addr, cr2_or_gpa);\n\n __kvm_vcpu_wake_up(vcpu);\n\n mmput(mm);\n\nand mmput() can\u0027t drop the last reference to the page tables if the vCPU is\nstill alive, i.e. the vCPU won\u0027t get stuck tearing down page tables.\n\nAdd a helper to do the flushing, specifically to deal with \"wakeup all\"\nwork items, as they aren\u0027t actually work items, i.e. are never placed in a\nworkqueue. Trying to flush a bogus workqueue entry rightly makes\n__flush_work() complain (kudos to whoever added that sanity check).\n\nNote, commit 5f6de5cbebee (\"KVM: Prevent module exit until al\n---truncated---"
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"value": "AV:L - The vulnerability is reached exclusively through `/dev/kvm` ioctls (`KVM_CREATE_VM`/`KVM_CREATE_VCPU`/`KVM_SET_USER_MEMORY_REGION`/`KVM _RUN`) plus `close()` of the vCPU fd, all of which require an account on the host; there is no network, adjacent-network, or remote-peer data path into `virt/kvm/async_pf.c`.\nAC:L - The attacker controls both sides of the window \u2014 `madvise(MADV_PAGEOUT)` on its own guest memslot guarantees `__gfn_to_pfn_memslot()` returns async, queueing up to `ASYNC_PF_PER_VCPU` (64) work items per vCPU that each sleep in `get_user_pages_remote()` for the whole swap-in latency, while `close()` of the vCPU fd drives `__fput()`\u2192`module_put()` at a moment of the attacker\u0027s choosing. Nothing depends on a memory layout or system state the attacker cannot influence, and the flaw is unconditional on x86 since `CONFIG_KVM_ASYNC_PF` is `select`ed by `CONFIG_KVM`.\nPR:L - No capability check exists anywhere on the path \u2014 `kvm_dev_ioctl(KVM_CREATE_VM)`, `kvm_setup_async_pf()`, and vCPU teardown are all reachable by any user holding an open `/dev/kvm`, which distros grant to the ordinary `kvm` group and container/CI images commonly expose world-writable. The entire unsafe state that constitutes the bug \u2014 KVM module code still executing after the last `module_put()` \u2014 is created with zero privileges, so PR:L is selected as the higher-severity option over PR:H.\nUI:N - No victim action such as mounting a filesystem, opening a device, or plugging in hardware is required; `kvm_clear_async_pf_completion_queue()` and the premature `module_put()` run automatically from `__fput()`/`kvm_destroy_vm()` when the attacker\u0027s own process exits.\nS:U - The stale work callback and the freed module text/`async_pf_cache` slab are both host-kernel resources, so the flaw and its impact stay within a single security authority \u2014 this is a host-internal module-lifetime bug, not a guest-to-host or IOMMU boundary escape.\nC:H - This is a use-after-free in which `process_one_work()` dispatches `worker-\u003ecurrent_func()` into a freed vmalloc module region and `async_pf_execute()` continues touching `struct kvm_async_pf` after `kmem_cache_destroy()` has released the slab; controlling the reallocated module-alloc/vmalloc contents yields kernel-mode execution and thus arbitrary kernel memory disclosure.\nI:H - The stale callback writes through the freed object (`list_add_tail(\u0026apf-\u003elink, ...)`, `apf-\u003evcpu = NULL`) into slab pages already returned to the allocator and reissued to other consumers, and executing a freed function pointer as kernel text is a direct control-flow hijack primitive \u2014 both are arbitrary-write class outcomes.\nA:H - Jumping into unmapped or repurposed vmalloc memory produces an immediate oops/panic, `kmem_cache_destroy()` on the still-populated `async_pf_cache` corrupts allocator state, and the same path drives full `kvm_destroy_vm()` teardown from a shared `system_wq` worker, which the commit\u0027s own trace shows wedging a kworker for more than 120 seconds."
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{
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"metrics": [
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"cvssV3_1": {
"attackComplexity": "HIGH",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
}
},
{
"other": {
"content": {
"id": "CVE-2024-26976",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2025-02-05T21:06:50.709457Z",
"version": "2.0.3"
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"type": "ssvc"
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}
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"problemTypes": [
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"descriptions": [
{
"cweId": "CWE-400",
"description": "CWE-400 Uncontrolled Resource Consumption",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2024-06-18T18:41:30.452Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
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],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"versions": [
{
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{
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"status": "affected",
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{
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{
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"status": "affected",
"version": "af585b921e5d1e919947c4b1164b59507fe7cd7b",
"versionType": "git"
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{
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"versionType": "git"
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{
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"version": "af585b921e5d1e919947c4b1164b59507fe7cd7b",
"versionType": "git"
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{
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"version": "af585b921e5d1e919947c4b1164b59507fe7cd7b",
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{
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"status": "affected",
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{
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},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"virt/kvm/async_pf.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "2.6.38"
},
{
"lessThan": "2.6.38",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "4.19.*",
"status": "unaffected",
"version": "4.19.312",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.4.*",
"status": "unaffected",
"version": "5.4.274",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.215",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.154",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.84",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.24",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.7.*",
"status": "unaffected",
"version": "6.7.12",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.8.*",
"status": "unaffected",
"version": "6.8.3",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "6.9",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "4.19.312",
"versionStartIncluding": "2.6.38",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.4.274",
"versionStartIncluding": "2.6.38",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.10.215",
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{
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{
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{
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{
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],
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"operator": "OR"
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}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Always flush async #PF workqueue when vCPU is being destroyed\n\nAlways flush the per-vCPU async #PF workqueue when a vCPU is clearing its\ncompletion queue, e.g. when a VM and all its vCPUs is being destroyed.\nKVM must ensure that none of its workqueue callbacks is running when the\nlast reference to the KVM _module_ is put. Gifting a reference to the\nassociated VM prevents the workqueue callback from dereferencing freed\nvCPU/VM memory, but does not prevent the KVM module from being unloaded\nbefore the callback completes.\n\nDrop the misguided VM refcount gifting, as calling kvm_put_kvm() from\nasync_pf_execute() if kvm_put_kvm() flushes the async #PF workqueue will\nresult in deadlock. async_pf_execute() can\u0027t return until kvm_put_kvm()\nfinishes, and kvm_put_kvm() can\u0027t return until async_pf_execute() finishes:\n\n WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+0x2d/0x320 [kvm]\n Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass\n CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n Workqueue: events async_pf_execute [kvm]\n RIP: 0010:kvm_put_kvm+0x2d/0x320 [kvm]\n Call Trace:\n \u003cTASK\u003e\n async_pf_execute+0x198/0x260 [kvm]\n process_one_work+0x145/0x2d0\n worker_thread+0x27e/0x3a0\n kthread+0xba/0xe0\n ret_from_fork+0x2d/0x50\n ret_from_fork_asm+0x11/0x20\n \u003c/TASK\u003e\n ---[ end trace 0000000000000000 ]---\n INFO: task kworker/8:1:251 blocked for more than 120 seconds.\n Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\n \"echo 0 \u003e /proc/sys/kernel/hung_task_timeout_secs\" disables this message.\n task:kworker/8:1 state:D stack:0 pid:251 ppid:2 flags:0x00004000\n Workqueue: events async_pf_execute [kvm]\n Call Trace:\n \u003cTASK\u003e\n __schedule+0x33f/0xa40\n schedule+0x53/0xc0\n schedule_timeout+0x12a/0x140\n __wait_for_common+0x8d/0x1d0\n __flush_work.isra.0+0x19f/0x2c0\n kvm_clear_async_pf_completion_queue+0x129/0x190 [kvm]\n kvm_arch_destroy_vm+0x78/0x1b0 [kvm]\n kvm_put_kvm+0x1c1/0x320 [kvm]\n async_pf_execute+0x198/0x260 [kvm]\n process_one_work+0x145/0x2d0\n worker_thread+0x27e/0x3a0\n kthread+0xba/0xe0\n ret_from_fork+0x2d/0x50\n ret_from_fork_asm+0x11/0x20\n \u003c/TASK\u003e\n\nIf kvm_clear_async_pf_completion_queue() actually flushes the workqueue,\nthen there\u0027s no need to gift async_pf_execute() a reference because all\ninvocations of async_pf_execute() will be forced to complete before the\nvCPU and its VM are destroyed/freed. And that in turn fixes the module\nunloading bug as __fput() won\u0027t do module_put() on the last vCPU reference\nuntil the vCPU has been freed, e.g. if closing the vCPU file also puts the\nlast reference to the KVM module.\n\nNote that kvm_check_async_pf_completion() may also take the work item off\nthe completion queue and so also needs to flush the work queue, as the\nwork will not be seen by kvm_clear_async_pf_completion_queue(). Waiting\non the workqueue could theoretically delay a vCPU due to waiting for the\nwork to complete, but that\u0027s a very, very small chance, and likely a very\nsmall delay. kvm_arch_async_page_present_queued() unconditionally makes a\nnew request, i.e. will effectively delay entering the guest, so the\nremaining work is really just:\n\n trace_kvm_async_pf_completed(addr, cr2_or_gpa);\n\n __kvm_vcpu_wake_up(vcpu);\n\n mmput(mm);\n\nand mmput() can\u0027t drop the last reference to the page tables if the vCPU is\nstill alive, i.e. the vCPU won\u0027t get stuck tearing down page tables.\n\nAdd a helper to do the flushing, specifically to deal with \"wakeup all\"\nwork items, as they aren\u0027t actually work items, i.e. are never placed in a\nworkqueue. Trying to flush a bogus workqueue entry rightly makes\n__flush_work() complain (kudos to whoever added that sanity check).\n\nNote, commit 5f6de5cbebee (\"KVM: Prevent module exit until al\n---truncated---"
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The vulnerability is reached exclusively through `/dev/kvm` ioctls (`KVM_CREATE_VM`/`KVM_CREATE_VCPU`/`KVM_SET_USER_MEMORY_REGION`/`KVM _RUN`) plus `close()` of the vCPU fd, all of which require an account on the host; there is no network, adjacent-network, or remote-peer data path into `virt/kvm/async_pf.c`.\nAC:L - The attacker controls both sides of the window \u2014 `madvise(MADV_PAGEOUT)` on its own guest memslot guarantees `__gfn_to_pfn_memslot()` returns async, queueing up to `ASYNC_PF_PER_VCPU` (64) work items per vCPU that each sleep in `get_user_pages_remote()` for the whole swap-in latency, while `close()` of the vCPU fd drives `__fput()`\u2192`module_put()` at a moment of the attacker\u0027s choosing. Nothing depends on a memory layout or system state the attacker cannot influence, and the flaw is unconditional on x86 since `CONFIG_KVM_ASYNC_PF` is `select`ed by `CONFIG_KVM`.\nPR:L - No capability check exists anywhere on the path \u2014 `kvm_dev_ioctl(KVM_CREATE_VM)`, `kvm_setup_async_pf()`, and vCPU teardown are all reachable by any user holding an open `/dev/kvm`, which distros grant to the ordinary `kvm` group and container/CI images commonly expose world-writable. The entire unsafe state that constitutes the bug \u2014 KVM module code still executing after the last `module_put()` \u2014 is created with zero privileges, so PR:L is selected as the higher-severity option over PR:H.\nUI:N - No victim action such as mounting a filesystem, opening a device, or plugging in hardware is required; `kvm_clear_async_pf_completion_queue()` and the premature `module_put()` run automatically from `__fput()`/`kvm_destroy_vm()` when the attacker\u0027s own process exits.\nS:U - The stale work callback and the freed module text/`async_pf_cache` slab are both host-kernel resources, so the flaw and its impact stay within a single security authority \u2014 this is a host-internal module-lifetime bug, not a guest-to-host or IOMMU boundary escape.\nC:H - This is a use-after-free in which `process_one_work()` dispatches `worker-\u003ecurrent_func()` into a freed vmalloc module region and `async_pf_execute()` continues touching `struct kvm_async_pf` after `kmem_cache_destroy()` has released the slab; controlling the reallocated module-alloc/vmalloc contents yields kernel-mode execution and thus arbitrary kernel memory disclosure.\nI:H - The stale callback writes through the freed object (`list_add_tail(\u0026apf-\u003elink, ...)`, `apf-\u003evcpu = NULL`) into slab pages already returned to the allocator and reissued to other consumers, and executing a freed function pointer as kernel text is a direct control-flow hijack primitive \u2014 both are arbitrary-write class outcomes.\nA:H - Jumping into unmapped or repurposed vmalloc memory produces an immediate oops/panic, `kmem_cache_destroy()` on the still-populated `async_pf_cache` corrupts allocator state, and the same path drives full `kvm_destroy_vm()` teardown from a shared `system_wq` worker, which the commit\u0027s own trace shows wedging a kworker for more than 120 seconds."
}
]
}
],
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"dateUpdated": "2026-08-05T11:28:48.394Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"url": "https://git.kernel.org/stable/c/ab2c2f5d9576112ad22cfd3798071cb74693b1f5"
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"url": "https://git.kernel.org/stable/c/82e25cc1c2e93c3023da98be282322fc08b61ffb"
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"url": "https://git.kernel.org/stable/c/f8730d6335e5f43d09151fca1f0f41922209a264"
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"url": "https://git.kernel.org/stable/c/b54478d20375874aeee257744dedfd3e413432ff"
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"url": "https://git.kernel.org/stable/c/a75afe480d4349c524d9c659b1a5a544dbc39a98"
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{
"url": "https://git.kernel.org/stable/c/4f3a3bce428fb439c66a578adc447afce7b4a750"
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{
"url": "https://git.kernel.org/stable/c/caa9af2e27c275e089d702cfbaaece3b42bca31b"
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{
"url": "https://git.kernel.org/stable/c/3d75b8aa5c29058a512db29da7cbee8052724157"
}
],
"title": "KVM: Always flush async #PF workqueue when vCPU is being destroyed",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"cveId": "CVE-2024-26976",
"datePublished": "2024-05-01T05:20:24.025Z",
"dateReserved": "2024-02-19T14:20:24.203Z",
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"state": "PUBLISHED"
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}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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