kvm: iommu: fix the third parameter of kvm_iommu_put_pages (CVE-2014-3601)

commit 350b8bdd689cd2ab2c67c8a86a0be86cfa0751a7 upstream.

The third parameter of kvm_iommu_put_pages is wrong,
It should be 'gfn - slot->base_gfn'.

By making gfn very large, malicious guest or userspace can cause kvm to
go to this error path, and subsequently to pass a huge value as size.
Alternatively if gfn is small, then pages would be pinned but never
unpinned, causing host memory leak and local DOS.

Passing a reasonable but large value could be the most dangerous case,
because it would unpin a page that should have stayed pinned, and thus
allow the device to DMA into arbitrary memory.  However, this cannot
happen because of the condition that can trigger the error:

- out of memory (where you can't allocate even a single page)
  should not be possible for the attacker to trigger

- when exceeding the iommu's address space, guest pages after gfn
  will also exceed the iommu's address space, and inside
  kvm_iommu_put_pages() the iommu_iova_to_phys() will fail.  The
  page thus would not be unpinned at all.

Reported-by: Jack Morgenstein <jackm@mellanox.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index 5dbb35d..c946700 100644 (file)
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -61,6 +61,14 @@ static pfn_t kvm_pin_pages(struct kvm *kvm, struct kvm_memory_slot *slot,
        return pfn;
 }
 
        return pfn;
 }
 

+static void kvm_unpin_pages(struct kvm *kvm, pfn_t pfn, unsigned long npages)
+{
+       unsigned long i;
+
+       for (i = 0; i < npages; ++i)
+               kvm_release_pfn_clean(pfn + i);
+}
+

 int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
 {
        gfn_t gfn, end_gfn;
 int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
 {
        gfn_t gfn, end_gfn;


@@ -121,6 +129,7 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
                if (r) {
                        printk(KERN_ERR "kvm_iommu_map_address:"
                               "iommu failed to map pfn=%llx\n", pfn);
                if (r) {
                        printk(KERN_ERR "kvm_iommu_map_address:"
                               "iommu failed to map pfn=%llx\n", pfn);

+                       kvm_unpin_pages(kvm, pfn, page_size);

                        goto unmap_pages;
                }
 
                        goto unmap_pages;
                }
 


@@ -132,7 +141,7 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
        return 0;
 
 unmap_pages:
        return 0;
 
 unmap_pages:

-       kvm_iommu_put_pages(kvm, slot->base_gfn, gfn);
+       kvm_iommu_put_pages(kvm, slot->base_gfn, gfn - slot->base_gfn);

        return r;
 }
 
        return r;
 }
 


@@ -273,14 +282,6 @@ out_unlock:
        return r;
 }
 
        return r;
 }
 

-static void kvm_unpin_pages(struct kvm *kvm, pfn_t pfn, unsigned long npages)
-{
-       unsigned long i;
-
-       for (i = 0; i < npages; ++i)
-               kvm_release_pfn_clean(pfn + i);
-}
-

 static void kvm_iommu_put_pages(struct kvm *kvm,
                                gfn_t base_gfn, unsigned long npages)
 {
 static void kvm_iommu_put_pages(struct kvm *kvm,
                                gfn_t base_gfn, unsigned long npages)
 {