Security update for xen (important)

This update for xen to version 4.7.3 fixes several issues.

These security issues were fixed:

• CVE-2017-12135: Unbounded recursion in grant table code allowed a
  malicious guest to crash the host or potentially escalate
  privileges/leak information (XSA-226, bsc#1051787).
• CVE-2017-12137: Incorrectly-aligned updates to pagetables allowed for
  privilege escalation (XSA-227, bsc#1051788).
• CVE-2017-12136: Race conditions with maptrack free list handling allows
  a malicious guest administrator to crash the host or escalate their
  privilege to that of the host (XSA-228, bsc#1051789).
• CVE-2017-11434: The dhcp_decode function in slirp/bootp.c allowed local
  guest OS users to cause a denial of service (out-of-bounds read) via a
  crafted DHCP
  options string (bsc#1049578).
• CVE-2017-10664: qemu-nbd did not ignore SIGPIPE, which allowed remote
  attackers to cause a denial of service (daemon crash) by disconnecting
  during a server-to-client reply attempt (bsc#1046637).
• CVE-2017-12855: Premature clearing of GTF_writing / GTF_reading lead to
  potentially leaking sensitive information (XSA-230 CVE-2017-12855).

These non-security issues were fixed:

• bsc#1055695: XEN: 11SP4 and 12SP3 HVM guests can not be restored after
  the save using xl stack
• bsc#1035231: Migration of HVM domU did not use superpages on destination
  dom0
• bsc#1002573: Optimized LVM functions in block-dmmd block-dmmd
• bsc#1037840: Xen-detect always showed HVM for PV guests

This update was imported from the SUSE:SLE-12-SP2:Update update project.