Patch "arm: KVM: Fix incorrect device to IPA mapping" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

arm: KVM: Fix incorrect device to IPA mapping

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm-kvm-fix-incorrect-device-to-ipa-mapping.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marek Majtyka <[email protected]>
Date: Wed, 16 Sep 2015 12:04:55 +0200
Subject: arm: KVM: Fix incorrect device to IPA mapping

From: Marek Majtyka <[email protected]>

commit ca09f02f122b2ecb0f5ddfc5fd47b29ed657d4fd upstream.

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).

---
 arch/arm/kvm/mmu.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -1792,8 +1792,10 @@ int kvm_arch_prepare_memory_region(struc
 		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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/arm-kvm-fix-incorrect-device-to-ipa-mapping.patch