In the Linux kernel, the following vulnerability has been resolved:
KVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU
Zap both valid and invalid roots when zapping/unmapping a gfn range, as
KVM must ensure it holds no references to the freed page after returning
from the unmap operation. Most notably, the TDP MMU doesn't zap invalid
roots in mmu_notifier callbacks. This leads to use-after-free and other
issues if the mmu_notifier runs to completion while an invalid root
zapper yields as KVM fails to honor the requirement that there must be
_no_ references to the page after the mmu_notifier returns.
The bug is most easily reproduced by hacking KVM to cause a collision
between set_nx_huge_pages() and kvm_mmu_notifier_release(), but the bug
exists between kvm_mmu_notifier_invalidate_range_start() and memslot
updates as well. Invalidating a root ensures pages aren't accessible by
the guest, and KVM won't read or write page data itself, but KVM will
trigger e.g. kvm_set_pfn_dirty() when zapping SPTEs, and thus completing
a zap of an invalid root _after_ the mmu_notifier returns is fatal.
WARNING: CPU: 24 PID: 1496 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:173 [kvm]
RIP: 0010:kvm_is_zone_device_pfn+0x96/0xa0 [kvm]
Call Trace:
<TASK>
kvm_set_pfn_dirty+0xa8/0xe0 [kvm]
__handle_changed_spte+0x2ab/0x5e0 [kvm]
__handle_changed_spte+0x2ab/0x5e0 [kvm]
__handle_changed_spte+0x2ab/0x5e0 [kvm]
zap_gfn_range+0x1f3/0x310 [kvm]
kvm_tdp_mmu_zap_invalidated_roots+0x50/0x90 [kvm]
kvm_mmu_zap_all_fast+0x177/0x1a0 [kvm]
set_nx_huge_pages+0xb4/0x190 [kvm]
param_attr_store+0x70/0x100
module_attr_store+0x19/0x30
kernfs_fop_write_iter+0x119/0x1b0
new_sync_write+0x11c/0x1b0
vfs_write+0x1cc/0x270
ksys_write+0x5f/0xe0
do_syscall_64+0x38/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae
</TASK>
Metrics
Affected Vendors & Products
References
History
Mon, 24 Mar 2025 18:15:00 +0000
Type | Values Removed | Values Added |
---|---|---|
First Time appeared |
Linux
Linux linux Kernel |
|
CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
Vendors & Products |
Linux
Linux linux Kernel |
Tue, 04 Mar 2025 03:45:00 +0000
Type | Values Removed | Values Added |
---|---|---|
Metrics |
ssvc
|
Fri, 28 Feb 2025 01:30:00 +0000
Type | Values Removed | Values Added |
---|---|---|
References |
| |
Metrics |
threat_severity
|
threat_severity
|
Thu, 27 Feb 2025 19:45:00 +0000
Type | Values Removed | Values Added |
---|---|---|
Weaknesses | CWE-416 | |
Metrics |
cvssV3_1
|
Wed, 26 Feb 2025 02:15:00 +0000
Type | Values Removed | Values Added |
---|---|---|
Description | In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU Zap both valid and invalid roots when zapping/unmapping a gfn range, as KVM must ensure it holds no references to the freed page after returning from the unmap operation. Most notably, the TDP MMU doesn't zap invalid roots in mmu_notifier callbacks. This leads to use-after-free and other issues if the mmu_notifier runs to completion while an invalid root zapper yields as KVM fails to honor the requirement that there must be _no_ references to the page after the mmu_notifier returns. The bug is most easily reproduced by hacking KVM to cause a collision between set_nx_huge_pages() and kvm_mmu_notifier_release(), but the bug exists between kvm_mmu_notifier_invalidate_range_start() and memslot updates as well. Invalidating a root ensures pages aren't accessible by the guest, and KVM won't read or write page data itself, but KVM will trigger e.g. kvm_set_pfn_dirty() when zapping SPTEs, and thus completing a zap of an invalid root _after_ the mmu_notifier returns is fatal. WARNING: CPU: 24 PID: 1496 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:173 [kvm] RIP: 0010:kvm_is_zone_device_pfn+0x96/0xa0 [kvm] Call Trace: <TASK> kvm_set_pfn_dirty+0xa8/0xe0 [kvm] __handle_changed_spte+0x2ab/0x5e0 [kvm] __handle_changed_spte+0x2ab/0x5e0 [kvm] __handle_changed_spte+0x2ab/0x5e0 [kvm] zap_gfn_range+0x1f3/0x310 [kvm] kvm_tdp_mmu_zap_invalidated_roots+0x50/0x90 [kvm] kvm_mmu_zap_all_fast+0x177/0x1a0 [kvm] set_nx_huge_pages+0xb4/0x190 [kvm] param_attr_store+0x70/0x100 module_attr_store+0x19/0x30 kernfs_fop_write_iter+0x119/0x1b0 new_sync_write+0x11c/0x1b0 vfs_write+0x1cc/0x270 ksys_write+0x5f/0xe0 do_syscall_64+0x38/0xc0 entry_SYSCALL_64_after_hwframe+0x44/0xae </TASK> | |
Title | KVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU | |
References |
|

Status: PUBLISHED
Assigner: Linux
Published: 2025-02-26T01:54:11.651Z
Updated: 2025-02-27T18:22:35.903Z
Reserved: 2025-02-26T01:48:21.519Z
Link: CVE-2021-47639

Updated: 2025-02-27T18:17:54.139Z

Status : Analyzed
Published: 2025-02-26T06:37:05.677
Modified: 2025-03-24T17:47:07.143
Link: CVE-2021-47639
