diff options
| author | Michael S. Tsirkin <mst@redhat.com> | 2010-10-25 03:21:24 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-12-09 13:32:44 -0800 |
| commit | e04e1834f740d225f6c70e6a49643261e7ee6a74 (patch) | |
| tree | 4a38278552bbdad5c478b617240a043b3af4a21e /arch | |
| parent | f0b7bc25f0b0b14f2a9104d5d99c9dee1678fdb0 (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>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/x86.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a4a427bea46e..acc64063c89d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2912,10 +2912,6 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_memslots *slots, *old_slots; unsigned long *dirty_bitmap; - spin_lock(&kvm->mmu_lock); - kvm_mmu_slot_remove_write_access(kvm, log->slot); - spin_unlock(&kvm->mmu_lock); - r = -ENOMEM; dirty_bitmap = vmalloc(n); if (!dirty_bitmap) @@ -2937,6 +2933,10 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, 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 = -EFAULT; if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) { vfree(dirty_bitmap); |