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CVE-2024-26976— KVM: Always flush async #PF workqueue when vCPU is being destroyed

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.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于当 vCPU 被销毁时，没有刷新异步 #PF 工作队列。

CVSS 7.8 · High EPSS 0.26% · P17

Possible ATT&CK Techniques 1 AI

T1059 · Command and Scripting Interpreter

Affected Version Matrix 20

VendorProduct Version RangeStatus
Linux Linux af585b921e5d1e919947c4b1164b59507fe7cd7b< ab2c2f5d9576112ad22cfd3798071cb74693b1f5 affected
af585b921e5d1e919947c4b1164b59507fe7cd7b< 82e25cc1c2e93c3023da98be282322fc08b61ffb affected
af585b921e5d1e919947c4b1164b59507fe7cd7b< f8730d6335e5f43d09151fca1f0f41922209a264 affected
af585b921e5d1e919947c4b1164b59507fe7cd7b< 83d3c5e309611ef593e2fcb78444fc8ceedf9bac affected
af585b921e5d1e919947c4b1164b59507fe7cd7b< b54478d20375874aeee257744dedfd3e413432ff affected
af585b921e5d1e919947c4b1164b59507fe7cd7b< a75afe480d4349c524d9c659b1a5a544dbc39a98 affected
af585b921e5d1e919947c4b1164b59507fe7cd7b< 4f3a3bce428fb439c66a578adc447afce7b4a750 affected
af585b921e5d1e919947c4b1164b59507fe7cd7b< caa9af2e27c275e089d702cfbaaece3b42bca31b affected
… +12 more rows
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I. Basic Information for CVE-2024-26976

Vulnerability Information
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Vulnerability Title
KVM: Always flush async #PF workqueue when vCPU is being destroyed
Source: CVE Program / CVE List V5
Vulnerability Description
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---
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于当 vCPU 被销毁时，没有刷新异步 #PF 工作队列。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux af585b921e5d1e919947c4b1164b59507fe7cd7b ~ ab2c2f5d9576112ad22cfd3798071cb74693b1f5 -
Linux Linux 2.6.38 -

II. Public POCs for CVE-2024-26976

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III. Intelligence Information for CVE-2024-26976

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Mailing List Discussions for CVE-2024-26976 (2)

Other References for CVE-2024-26976 (9)

Same Patch Batch · Linux · 2024-05-01 · 159 CVEs total

CVE-2024-27388 9.8 CRITICAL SUNRPC: fix some memleaks in gssx_dec_option_array
CVE-2024-26953 9.8 CRITICAL net: esp: fix bad handling of pages from page_pool
CVE-2024-26931 8.8 HIGH scsi: qla2xxx: Fix command flush on cable pull
CVE-2024-27053 8.8 HIGH wifi: wilc1000: fix RCU usage in connect path
CVE-2024-26990 8.8 HIGH KVM: x86/mmu: Write-protect L2 SPTEs in TDP MMU when clearing dirty status
CVE-2024-26952 8.3 HIGH ksmbd: fix potencial out-of-bounds when buffer offset is invalid
CVE-2024-26936 8.2 HIGH ksmbd: validate request buffer size in smb2_allocate_rsp_buf()
CVE-2024-27018 8.2 HIGH netfilter: br_netfilter: skip conntrack input hook for promisc packets
CVE-2024-26980 8.2 HIGH ksmbd: fix slab-out-of-bounds in smb2_allocate_rsp_buf
CVE-2024-26954 8.1 HIGH ksmbd: fix slab-out-of-bounds in smb_strndup_from_utf16()
CVE-2024-26994 7.8 HIGH speakup: Avoid crash on very long word
CVE-2024-26966 7.8 HIGH clk: qcom: mmcc-apq8084: fix terminating of frequency table arrays
CVE-2024-26974 7.8 HIGH crypto: qat - resolve race condition during AER recovery
CVE-2024-27062 7.8 HIGH nouveau: lock the client object tree.
CVE-2024-27061 7.8 HIGH crypto: sun8i-ce - Fix use after free in unprepare
CVE-2024-26983 7.8 HIGH bootconfig: use memblock_free_late to free xbc memory to buddy
CVE-2024-27058 7.8 HIGH tmpfs: fix race on handling dquot rbtree
CVE-2024-27056 7.8 HIGH wifi: iwlwifi: mvm: ensure offloading TID queue exists
CVE-2024-27017 7.8 HIGH netfilter: nft_set_pipapo: walk over current view on netlink dump
CVE-2024-27019 7.8 HIGH netfilter: nf_tables: Fix potential data-race in __nft_obj_type_get()

Showing top 20 of 159 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2024-26976

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