From: Michael S. Tsirkin Date: Mon, 25 Oct 2010 01:21:24 +0000 (+0200) Subject: KVM: Write protect memory after slot swap X-Git-Tag: v2.6.35.10~119 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e110ca176b8d6499d9b6d69a5e1b9055f10e6a1b;p=karo-tx-linux.git 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 Signed-off-by: Avi Kivity Signed-off-by: Greg Kroah-Hartman Signed-off-by: Andi Kleen --- 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;