From 350b8bdd689cd2ab2c67c8a86a0be86cfa0751a7 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Tue, 19 Aug 2014 19:14:50 +0800 Subject: kvm: iommu: fix the third parameter of kvm_iommu_put_pages (CVE-2014-3601) 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 Cc: stable@vger.kernel.org Signed-off-by: Michael S. Tsirkin Signed-off-by: Paolo Bonzini --- virt/kvm/iommu.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) (limited to 'virt/kvm/iommu.c') diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c index 0df7d4b34dfe..714b94932312 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) { -- cgit v1.2.3