Do not allow resetting dirty GFNs belonging to a memslot that does not enable dirty tracking. vCPUs' dirty rings are shared between userspace and KVM. After KVM sets dirtied entries in the dirty rings, userspace is responsible for harvesting/resetting the dirtied entries and calling the ioctl KVM_RESET_DIRTY_RINGS to inform KVM to advance the reset_index in the dirty rings and invoke kvm_arch_mmu_enable_log_dirty_pt_masked() to clear the SPTEs' dirty bits or perform write protection of GFNs. Although KVM does not set dirty entries for GFNs in a memslot that does not enable dirty tracking, userspace can write arbitrary data into the dirty ring. This makes it possible for misbehaving userspace to specify that it has harvested a GFN belonging to such a memslot. When this happens, KVM will be asked to clear dirty bits or perform write protection for GFNs in a memslot that does not enable dirty tracking, which is not desired. For TDX, this unexpected resetting of dirty GFNs could cause inconsistency between the mirror SPTE and the external SPTE in hardware (e.g., the mirror SPTE has no write bit while it is writable in the external SPTE in hardware). When kvm_dirty_log_manual_protect_and_init_set() is true and when huge pages are enabled in TDX, this could even lead to kvm_mmu_slot_gfn_write_protect() being called and the external SPTE being removed. Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx> --- virt/kvm/dirty_ring.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c index d14ffc7513ee..d52093b5ec73 100644 --- a/virt/kvm/dirty_ring.c +++ b/virt/kvm/dirty_ring.c @@ -66,7 +66,13 @@ static void kvm_reset_dirty_gfn(struct kvm *kvm, u32 slot, u64 offset, u64 mask) memslot = id_to_memslot(__kvm_memslots(kvm, as_id), id); - if (!memslot || (offset + __fls(mask)) >= memslot->npages) + /* + * Userspace can write arbitrary data into the dirty ring, making it + * possible for misbehaving userspace to try to reset an out-of-memslot + * GFN or a GFN in a memslot that isn't being dirty-logged. + */ + if (!memslot || (offset + __fls(mask)) >= memslot->npages || + !kvm_slot_dirty_track_enabled(memslot)) return; KVM_MMU_LOCK(kvm); -- 2.43.2
