Security update for xen (important)

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-5753, CVE-2017-5715, CVE-2017-5754: Prevent information leaks
  via side effects of speculative execution, aka "Spectre" and "Meltdown"
  attacks (bsc#1074562, bsc#1068032)
• CVE-2018-5683: The vga_draw_text function allowed local OS guest
  privileged users to cause a denial of service (out-of-bounds read and
  QEMU process crash) by leveraging improper memory address validation
  (bsc#1076116).
• CVE-2017-18030: The cirrus_invalidate_region function allowed local OS
  guest privileged users to cause a denial of service (out-of-bounds array
  access and QEMU process crash) via vectors related to negative pitch
  (bsc#1076180).
• CVE-2017-15595: x86 PV guest OS users were able to cause a DoS
  (unbounded recursion, stack consumption, and hypervisor crash) or
  possibly gain privileges via crafted page-table stacking (bsc#1061081)
• CVE-2017-17566: Prevent PV guest OS users to cause a denial of service
  (host OS crash) or gain host OS privileges in shadow mode by mapping a
  certain auxiliary page (bsc#1070158).
• CVE-2017-17563: Prevent guest OS users to cause a denial of service
  (host OS crash) or gain host OS privileges by leveraging an incorrect
  mask for reference-count overflow checking in shadow mode (bsc#1070159).
• CVE-2017-17564: Prevent guest OS users to cause a denial of service
  (host OS crash) or gain host OS privileges by leveraging incorrect error
  handling for reference counting in shadow mode (bsc#1070160).
• CVE-2017-17565: Prevent PV guest OS users to cause a denial of service
  (host OS crash) if shadow mode and log-dirty mode are in place, because
  of an incorrect assertion related to M2P (bsc#1070163).
• Added missing intermediate preemption checks for guest requesting
  removal of memory. This allowed malicious guest administrator to cause
  denial of service due to the high cost of this operation (bsc#1080635).
• Because of XEN not returning the proper error messages when
  transitioning grant tables from v2 to v1 a malicious guest was able to
  cause DoS or potentially allowed for privilege escalation as well as
  information leaks (bsc#1080662).

This non-security issue was fixed:

• bsc#1035442: Increased the value of LIBXL_DESTROY_TIMEOUT from 10 to 100
  seconds. If many domUs shutdown in parallel the backends couldn’t keep up