[PATCH 3.13 002/187] kvm: iommu: fix the third parameter of kvm_iommu_put_pages (CVE-2014-3601)

Kamal Mostafa
2014-09-15T23:23:08Z

From: "Michael S. Tsirkin" <mst@redhat.com>

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: Kamal Mostafa <kamal@canonical.com>
---
virt/kvm/iommu.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index 0df7d4b..714b949 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -61,6 +61,14 @@ static pfn_t kvm_pin_pages(struct kvm_memory_slot *slot, gfn_t gfn,
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;
@@ -123,6 +131,7 @@ 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);
+ kvm_unpin_pages(kvm, pfn, page_size);
goto unmap_pages;
}

@@ -134,7 +143,7 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
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;
}

@@ -266,14 +275,6 @@ out_unlock:
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)
{
--
1.9.1