2025-02-26 01:54:11
Linux
PUBLISHED
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 doesnt 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 arent accessible by
the guest, and KVM wont 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: