CVE-2021-47639: KVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU
First published: Wed Feb 26 2025(Updated: )
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>
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Kernel | ||
| Linux Kernel | >=5.13<5.15.33 | |
| Linux Kernel | >=5.16<5.16.19 | |
| Linux Kernel | >=5.17<5.17.2 |
Never miss a vulnerability like this again
Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.
Reference Links
Frequently Asked Questions
What is the severity of CVE-2021-47639?
CVE-2021-47639 has a high severity rating due to potential exploitation in the Linux kernel affecting memory management.
How do I fix CVE-2021-47639?
To fix CVE-2021-47639, update the Linux kernel to the latest version where the vulnerability has been resolved.
Which systems are affected by CVE-2021-47639?
CVE-2021-47639 affects systems running certain versions of the Linux kernel that use KVM for virtual memory management.
What type of vulnerability is CVE-2021-47639?
CVE-2021-47639 is a memory management vulnerability related to the KVM module in the Linux kernel.
Can CVE-2021-47639 lead to remote code execution?
While CVE-2021-47639 primarily affects memory management, successful exploitation could potentially lead to unauthorized access or denial of service.
- agent/first-publish-date
- agent/type
- agent/title
- agent/references
- agent/author
- agent/source
- agent/description
- agent/severity
- agent/guess-ai
- agent/software-canonical-lookup
- collector/mitre-cve
- source/MITRE
- agent/weakness
- agent/last-modified-date
- agent/remedy
- agent/softwarecombine
- agent/event
- agent/tags
- collector/nvd-api
- source/NVD
- vendor/linux foundation
- canonical/linux kernel
- vendor/linux
- version/linux kernel/5.13
- version/linux kernel/5.16
- version/linux kernel/5.17