Security update for xen (important)

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-7980: An out-of-bounds r/w access issues in the Cirrus CLGD
  54xx VGA Emulator support allowed privileged user inside guest to use
  this flaw to crash the Qemu process resulting in DoS or potentially
  execute arbitrary code on a host with privileges of Qemu process on the
  host (bsc#1035483).
• A malicious 64-bit PV guest may be able to access all of system memory,
  allowing for all of privilege escalation, host crashes, and information
  leaks by placing a IRET hypercall in the middle of a multicall batch
  (XSA-213, bsc#1034843)
• A malicious pair of guests may be able to access all of system memory,
  allowing for all of privilege escalation, host crashes, and information
  leaks because of a missing check when transfering pages via
  GNTTABOP_transfer (XSA-214, bsc#1034844).
• Incorrect checks when handling exceptions allowed a malicious or buggy
  64-bit PV guest to modify part of a physical memory page not belonging
  to it, potentially allowing for all of privilege escalation, host or
  other guest crashes, and information leaks (XSA-215, bsc#1034845)
• CVE-2017-7718: hw/display/cirrus_vga_rop.h allowed local guest OS
  privileged users to cause a denial of service (out-of-bounds read and
  QEMU process crash) via vectors related to copying VGA data via the
  cirrus_bitblt_rop_fwd_transp_ and cirrus_bitblt_rop_fwd_ functions
  (bsc#1034994).

This non-security issue was fixed:

• bsc#1029827: Additional xenstore fixes