(RHSA-2016:0024) Important: kernel security and bug fix update

The kernel packages contain the Linux kernel, the core of any Linux
operating system.

• It was found that the x86 ISA (Instruction Set Architecture) is prone to
  a denial of service attack inside a virtualized environment in the form of
  an infinite loop in the microcode due to the way (sequential) delivering of
  benign exceptions such as #AC (alignment check exception) and #DB (debug
  exception) is handled. A privileged user inside a guest could use these
  flaws to create denial of service conditions on the host kernel.
  (CVE-2015-5307, CVE-2015-8104, Important)

Red Hat would like to thank Ben Serebrin of Google Inc. for reporting the
CVE-2015-5307 issue.

This update also fixes the following bugs:

• When doing TSO/GSO in the presence of VLAN headers on a macvtap device,
  the header offsets were incorrectly calculated. As a consequence, when 2
  guests on the same host communicated over a guest configured VLAN,
  performance dropped to about 1 Mbps. A set of patches has been provided to
  fix this bug, and network performance with VLAN tags now works with optimal
  performance. (BZ#1215914)

• Prior to this update, TSO acceleration features have been removed from
  the VLAN device which caused that VLAN performance on top of a virtio
  device was much lower than that of a virtio device itself. This update
  re-enables TSO acceleration features, and performance of VLAN devices on
  top of a virtio device has thus been restored. (BZ#1240988)

• With an IPv6 address on a bond and a slave failover, Unsolicited Neighbor
  Advertisement (UNA) was previously sent using the link global IPv6 address
  as source address. The underlying source code has been patched, and, after
  the failover in bonding, UNA is sent using both the corresponding link IPv6
  address and global IPv6 address of bond0 and bond0.vlan. (BZ#1258480)

• Previously, Human Interface Device (HID) would run a report on an
  unaligned buffer, which could cause a page fault interrupt and an oops when
  the end of the report was read. This update fixes this bug by padding the
  end of the report with extra bytes, so the reading of the report never
  crosses a page boundary. As a result, a page fault and subsequent oops no
  longer occur. (BZ#1268202)

• Inside hugetlb, region data structures were protected by a combination of
  a memory map semaphore and a single hugetlb instance mutex. However, a
  page-fault scalability improvement backported to the kernel on previous
  releases removed the single hugetlb instance mutex and introduced a new
  mutex table, making the locking combination insufficient, leading to
  possible race windows that could cause corruption and undefined behavior.
  The problem could be seen for example with software mapping or re-mapping
  hugetlb areas with concurrent threads reading/writing to same areas causing
  page faults. This update fixes the problem by introducing now a required
  spinlock to the region tracking functions for proper serialization. The
  problem only affects software using huge pages through hugetlb interface.
  (BZ#1274597)

• Previously, VLAN stacked on the macvlan or macvtap device did not work
  for devices that implement and use VLAN filters. As a consequence, macvtap
  passthrough mode failed to transfer VLAN packets over the be2net driver.
  This update implements VLAN ndo calls to the macvlan driver to pass
  appropriate VLAN tag IDs to lower devices. As a result, macvtap transfers
  VLAN packets over be2net successfully. (BZ#1280205)

All kernel users are advised to upgrade to these updated packages, which
contain backported patches to correct these issues. The system must be
rebooted for this update to take effect.