Security update for xen (important)

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2018-8897: Prevent mishandling of debug exceptions on x86 (XSA-260,
  bsc#1090820)
• Handle HPET timers in IO-APIC mode correctly to prevent malicious or
  buggy HVM guests from causing a hypervisor crash or potentially
  privilege escalation/information leaks (XSA-261, bsc#1090822)
• Prevent unbounded loop, induced by qemu allowing an attacker to
  permanently keep a physical CPU core busy (XSA-262, bsc#1090823)
• CVE-2018-10472: x86 HVM guest OS users (in certain configurations) were
  able to read arbitrary dom0 files via QMP live insertion of a CDROM, in
  conjunction with specifying the target file as the backing file of a
  snapshot (bsc#1089152).
• CVE-2018-10471: x86 PV guest OS users were able to cause a denial of
  service (out-of-bounds zero write and hypervisor crash) via unexpected
  INT 80 processing, because of an incorrect fix for CVE-2017-5754
  (bsc#1089635).
• CVE-2018-7550: The load_multiboot function allowed local guest OS users
  to execute arbitrary code on the host via a mh_load_end_addr value
  greater than mh_bss_end_addr, which triggers an out-of-bounds read or
  write memory access (bsc#1083292).

This non-security issue was fixed:

• bsc#1072834: Prevent unchecked MSR access error
• bsc#1057493: Prevent DomU crashes
• bsc#1086107: Fixed problems with backports for XSA-246 and XSA-247