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

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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>
Cc: stable@vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2014-08-19 19:14:50 +08:00 committed by Paolo Bonzini
parent 7d1311b93e
commit 350b8bdd68
1 changed files with 10 additions and 9 deletions
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19
virt/kvm/iommu.c
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@ -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)
{