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authorMichael S. Tsirkin <mst@redhat.com>2010-10-25 03:21:24 +0200
committerMarcelo Tosatti <mtosatti@redhat.com>2010-11-05 14:42:25 -0200
commitedde99ce05290e50ce0b3495d209e54e6349ab47 (patch)
treeefb966684a2999613ab81e5d30a9118acdb9fbef /arch
parentff8b16d7e15a8ba2a6086645614a483e048e3fbf (diff)
KVM: Write protect memory after slot swap
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. KVM-Stable-Tag. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/x86.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2288ad829b32..b0818f672064 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3169,10 +3169,6 @@ 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)
@@ -3194,6 +3190,10 @@ 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);