References: bsc#969125 CVE-2015-8817

Subject: exec: Respect as_translate_internal length clamp
From: Peter Crosthwaite peter.crosthwaite@xilinx.com Mon Mar 16 22:35:54 2015 -0700
Date: Mon Apr 27 18:24:19 2015 +0200:
Git: 23820dbfc79d1c9dce090b4c555994f2bb6a69b3

address_space_translate_internal will clamp the *plen length argument
based on the size of the memory region being queried. The iommu walker
logic in addresss_space_translate was ignoring this by discarding the
post fn call value of *plen. Fix by just always using *plen as the
length argument throughout the fn, removing the len local variable.

This fixes a bootloader bug when a single elf section spans multiple
QEMU memory regions.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-Id: <1426570554-15940-1-git-send-email-peter.crosthwaite@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Index: xen-4.6.1-testing/tools/qemu-xen-dir-remote/exec.c
===================================================================
--- xen-4.6.1-testing.orig/tools/qemu-xen-dir-remote/exec.c
+++ xen-4.6.1-testing/tools/qemu-xen-dir-remote/exec.c
@@ -363,7 +363,6 @@ MemoryRegion *address_space_translate(Ad
     IOMMUTLBEntry iotlb;
     MemoryRegionSection *section;
     MemoryRegion *mr;
-    hwaddr len = *plen;
 
     for (;;) {
         section = address_space_translate_internal(as->dispatch, addr, &addr, plen, true);
@@ -376,7 +375,7 @@ MemoryRegion *address_space_translate(Ad
         iotlb = mr->iommu_ops->translate(mr, addr, is_write);
         addr = ((iotlb.translated_addr & ~iotlb.addr_mask)
                 | (addr & iotlb.addr_mask));
-        len = MIN(len, (addr | iotlb.addr_mask) - addr + 1);
+        *plen = MIN(*plen, (addr | iotlb.addr_mask) - addr + 1);
         if (!(iotlb.perm & (1 << is_write))) {
             mr = &io_mem_unassigned;
             break;
@@ -387,10 +386,9 @@ MemoryRegion *address_space_translate(Ad
 
     if (xen_enabled() && memory_access_is_direct(mr, is_write)) {
         hwaddr page = ((addr & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE) - addr;
-        len = MIN(page, len);
+        *plen = MIN(page, *plen);
     }
 
-    *plen = len;
     *xlat = addr;
     return mr;
 }