KVM: unmap pages from the iommu when slots are removed

CVE-2012-2121

BugLink: http://bugs.launchpad.net/bugs/987569

commit 32f6daad4651a748a58a3ab6da0611862175722f upstream.

We've been adding new mappings, but not destroying old mappings.
This can lead to a page leak as pages are pinned using
get_user_pages, but only unpinned with put_page if they still
exist in the memslots list on vm shutdown.  A memslot that is
destroyed while an iommu domain is enabled for the guest will
therefore result in an elevated page reference count that is
never cleared.

Additionally, without this fix, the iommu is only programmed
with the first translation for a gpa.  This can result in
peer-to-peer errors if a mapping is destroyed and replaced by a
new mapping at the same gpa as the iommu will still be pointing
to the original, pinned memory address.

Signed-off-by: Alex Williamson <[email protected]>
Signed-off-by: Marcelo Tosatti <[email protected]>
[bwh: Backported to 2.6.32:
 - Adjust context
 - In __kvm_set_memory_region(), call kvm_iommu_unmap_pages()
   immediately before kvm_free_physmem_slot() which cleans up the old
   memory slot.  Make this dependent on CONFIG_DMAR, consistent with
   the use of kvm_iommu_map_pages().]
Signed-off-by: Luis Henriques <[email protected]>
Signed-off-by: Tim Gardner <[email protected]>

Author: awilliam

include/linux/kvm_host.h

@@ -426,6 +426,7 @@ void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id);
 #ifdef CONFIG_IOMMU_API
 int kvm_iommu_map_pages(struct kvm *kvm, gfn_t base_gfn,
 			unsigned long npages);
+void kvm_iommu_unmap_pages(struct kvm *kvm, struct kvm_memory_slot *slot);
 int kvm_iommu_map_guest(struct kvm *kvm);
 int kvm_iommu_unmap_guest(struct kvm *kvm);
 int kvm_assign_device(struct kvm *kvm,
@@ -440,6 +441,11 @@ static inline int kvm_iommu_map_pages(struct kvm *kvm,
 	return 0;
 }
 
+static inline void kvm_iommu_unmap_pages(struct kvm *kvm,
+					 struct kvm_memory_slot *slot)
+{
+}
+
 static inline int kvm_iommu_map_guest(struct kvm *kvm)
 {
 	return -ENODEV;

virt/kvm/iommu.c

@@ -207,13 +207,17 @@ static void kvm_iommu_put_pages(struct kvm *kvm,
 	iommu_unmap_range(domain, gfn_to_gpa(base_gfn), PAGE_SIZE * npages);
 }
 
+void kvm_iommu_unmap_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	kvm_iommu_put_pages(kvm, slot->base_gfn, slot->npages);
+}
+
 static int kvm_iommu_unmap_memslots(struct kvm *kvm)
 {
 	int i;
 
 	for (i = 0; i < kvm->nmemslots; i++) {
-		kvm_iommu_put_pages(kvm, kvm->memslots[i].base_gfn,
-				    kvm->memslots[i].npages);
+		kvm_iommu_unmap_pages(kvm, &kvm->memslots[i]);
 	}
 
 	return 0;

virt/kvm/kvm_main.c

@@ -1338,6 +1338,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		goto out_free;
 	}
 
+#ifdef CONFIG_DMAR
+	/* unmap the pages in iommu page table */
+	if (!npages)
+		kvm_iommu_unmap_pages(kvm, &old);
+#endif
+
 	kvm_free_physmem_slot(&old, npages ? &new : NULL);
 	/* Slot deletion case: we have to update the current slot */
 	spin_lock(&kvm->mmu_lock);