arm: KVM: Fix incorrect device to IPA mapping

A critical bug has been found in device memory stage1 translation for
VMs with more then 4GB of address space. Once vm_pgoff size is smaller
then pa (which is true for LPAE case, u32 and u64 respectively) some
more significant bits of pa may be lost as a shift operation is performed
on u32 and later cast onto u64.

Example: vm_pgoff(u32)=0x00210030, PAGE_SHIFT=12
        expected pa(u64):   0x0000002010030000
        produced pa(u64):   0x0000000010030000

The fix is to change the order of operations (casting first onto phys_addr_t
and then shifting).

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
[maz: fixed changelog and patch formatting]
Cc: stable@vger.kernel.org
Signed-off-by: Marek Majtyka <marek.majtyka@tieto.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 7b4201294187..6984342da13d 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1792,8 +1792,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
                 if (vma->vm_flags & VM_PFNMAP) {
                         gpa_t gpa = mem->guest_phys_addr +
                                     (vm_start - mem->userspace_addr);
-                        phys_addr_t pa = (vma->vm_pgoff << PAGE_SHIFT) +
-                                         vm_start - vma->vm_start;
+                        phys_addr_t pa;
+
+                        pa = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
+                        pa += vm_start - vma->vm_start;
 
                         /* IO region dirty page logging not allowed */
                         if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES)