Code: int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
{
	gfn_t gfn, end_gfn;
	pfn_t pfn;
	int r = 0;
	struct iommu_domain *domain = kvm->arch.iommu_domain;
	int flags;

	/* check if iommu exists and in use */
	if (!domain)
		return 0;

	gfn     = slot->base_gfn;
	end_gfn = gfn + slot->npages;

	flags = IOMMU_READ;
	if (!(slot->flags & KVM_MEM_READONLY))
		flags |= IOMMU_WRITE;
	if (!kvm->arch.iommu_noncoherent)
		flags |= IOMMU_CACHE;


	while (gfn < end_gfn) {
		unsigned long page_size;

		/* Check if already mapped */
		if (iommu_iova_to_phys(domain, gfn_to_gpa(gfn))) {
			gfn += 1;
			continue;
		}

		/* Get the page size we could use to map */
		page_size = kvm_host_page_size(kvm, gfn);

		/* Make sure the page_size does not exceed the memslot */
		while ((gfn + (page_size >> PAGE_SHIFT)) > end_gfn)
			page_size >>= 1;

		/* Make sure gfn is aligned to the page size we want to map */
		while ((gfn << PAGE_SHIFT) & (page_size - 1))
			page_size >>= 1;

		/* Make sure hva is aligned to the page size we want to map */
		while (__gfn_to_hva_memslot(slot, gfn) & (page_size - 1))
			page_size >>= 1;

		/*
 		 * Pin all pages we are about to map in memory. This is
 		 * important because we unmap and unpin in 4kb steps later.
 		 */
		pfn = kvm_pin_pages(slot, gfn, page_size);
 		if (is_error_noslot_pfn(pfn)) {
 			gfn += 1;
 			continue;
		}

		/* Map into IO address space */
		r = iommu_map(domain, gfn_to_gpa(gfn), pfn_to_hpa(pfn),
			      page_size, flags);
 		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;
 		}
 
		gfn += page_size >> PAGE_SHIFT;


	}

	return 0;

unmap_pages:
	kvm_iommu_put_pages(kvm, slot->base_gfn, gfn - slot->base_gfn);
	return r;
}

Vulnerability Type: DoS 
CWE ID: CWE-189
Summary: The kvm_iommu_map_pages function in virt/kvm/iommu.c in the Linux kernel through 3.17.2 miscalculates the number of pages during the handling of a mapping failure, which allows guest OS users to cause a denial of service (host OS page unpinning) or possibly have unspecified other impact by leveraging guest OS privileges.  NOTE: this vulnerability exists because of an incorrect fix for CVE-2014-3601.
Commit Message: kvm: fix excessive pages un-pinning in kvm_iommu_map error path.

The third parameter of kvm_unpin_pages() when called from
kvm_iommu_map_pages() is wrong, it should be the number of pages to un-pin
and not the page size.

This error was facilitated with an inconsistent API: kvm_pin_pages() takes
a size, but kvn_unpin_pages() takes a number of pages, so fix the problem
by matching the two.

This was introduced by commit 350b8bd ("kvm: iommu: fix the third parameter
of kvm_iommu_put_pages (CVE-2014-3601)"), which fixes the lack of
un-pinning for pages intended to be un-pinned (i.e. memory leak) but
unfortunately potentially aggravated the number of pages we un-pin that
should have stayed pinned. As far as I understand though, the same
practical mitigations apply.

This issue was found during review of Red Hat 6.6 patches to prepare
Ksplice rebootless updates.

Thanks to Vegard for his time on a late Friday evening to help me in
understanding this code.

Fixes: 350b8bd ("kvm: iommu: fix the third parameter of... (CVE-2014-3601)")
Cc: stable@vger.kernel.org
Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Jamie Iles <jamie.iles@oracle.com>
Reviewed-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>