diff options
| author | Michael S. Tsirkin <mst@redhat.com> | 2010-10-25 03:21:24 +0200 |
|---|---|---|
| committer | Andi Kleen <ak@linux.intel.com> | 2010-12-14 23:40:08 +0100 |
| commit | e110ca176b8d6499d9b6d69a5e1b9055f10e6a1b (patch) | |
| tree | 2f7d3c2a351e668c2e9f1e7e55839de51b38b8ff /arch | |
| parent | e945dc312ad16872c7094990fd390ec0c3b5a6a0 (diff) | |
KVM: Write protect memory after slot swap
commit edde99ce05290e50ce0b3495d209e54e6349ab47 upstream.
I have observed the following bug trigger:
1. userspace calls GET_DIRTY_LOG
2. kvm_mmu_slot_remove_write_access is called and makes a page ro
3. page fault happens and makes the page writeable
fault is logged in the bitmap appropriately
4. kvm_vm_ioctl_get_dirty_log swaps slot pointers
a lot of time passes
5. guest writes into the page
6. userspace calls GET_DIRTY_LOG
At point (5), bitmap is clean and page is writeable,
thus, guest modification of memory is not logged
and GET_DIRTY_LOG returns an empty bitmap.
The rule is that all pages are either dirty in the current bitmap,
or write-protected, which is violated here.
It seems that just moving kvm_mmu_slot_remove_write_access down
to after the slot pointer swap should fix this bug.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/x86.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index be9251193d2a..ff274a142ed8 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2825,10 +2825,6 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, if (is_dirty) { struct kvm_memslots *slots, *old_slots; - spin_lock(&kvm->mmu_lock); - kvm_mmu_slot_remove_write_access(kvm, log->slot); - spin_unlock(&kvm->mmu_lock); - slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL); if (!slots) goto out_free; @@ -2841,6 +2837,11 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, synchronize_srcu_expedited(&kvm->srcu); dirty_bitmap = old_slots->memslots[log->slot].dirty_bitmap; kfree(old_slots); + + spin_lock(&kvm->mmu_lock); + kvm_mmu_slot_remove_write_access(kvm, log->slot); + spin_unlock(&kvm->mmu_lock); + } r = 0; |