Code:  static pfn_t kvm_pin_pages(struct kvm_memory_slot *slot, gfn_t gfn,
			   unsigned long size)
 {
 	gfn_t end_gfn;
 	pfn_t pfn;
 
 	pfn     = gfn_to_pfn_memslot(slot, gfn);
	end_gfn = gfn + (size >> PAGE_SHIFT);
 	gfn    += 1;
 
 	if (is_error_noslot_pfn(pfn))
		return pfn;

	while (gfn < end_gfn)
		gfn_to_pfn_memslot(slot, gfn++);

	return pfn;
}

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>