(RHSA-2015:2552) 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:

• On Intel Xeon v5 platforms, the processor frequency was always tied to
  the highest possible frequency. Switching p-states on these client
  platforms failed. This update sets the idle frequency, busy frequency, and
  processor frequency values by determining the range and adjusting the
  minimal and maximal percent limit values. Now, switching p-states on the
  aforementioned client platforms proceeds successfully. (BZ#1273926)

• Due to a validation error of in-kernel memory-mapped I/O (MMIO) tracing,
  a VM became previously unresponsive when connected to Red Hat Enterprise
  Virtualization Hypervisor. The provided patch fixes this bug by dropping
  the check in MMIO handler, and a VM continues running as expected.
  (BZ#1275150)

• Due to retry-able command errors, the NVMe driver previously leaked I/O
  descriptors and DMA mappings. As a consequence, the kernel could become
  unresponsive during the hot-unplug operation if a driver was removed.
  This update fixes the driver memory leak bug on command retries, and the
  kernel no longer hangs in this situation. (BZ#1279792)

• The hybrid_dma_data() function was not initialized before use, which
  caused an invalid memory access when hot-plugging a PCI card. As a
  consequence, a kernel oops occurred. The provided patch makes sure
  hybrid_dma_data() is initialized before use, and the kernel oops no longer
  occurs in this situation. (BZ#1279793)

• When running PowerPC (PPC) KVM guests and the host was experiencing a lot
  of page faults, for example because it was running low on memory, the host
  sometimes triggered an incorrect kind of interrupt in the guest: a data
  storage exception instead of a data segment exception. This caused a kernel
  panic of the PPC KVM guest. With this update, the host kernel synthesizes a
  segment fault if the corresponding Segment Lookaside Buffer (SLB) lookup
  fails, which prevents the kernel panic from occurring. (BZ#1281423)

• The kernel accessed an incorrect area of the khugepaged process causing
  Logical Partitioning (LPAR) to become unresponsive, and an oops occurred in
  medlp5. The backported upstream patch prevents an LPAR hang, and the oops
  no longer occurs. (BZ#1281424)

• When the sctp module was loaded and a route to an association endpoint
  was removed after receiving an Out-of-The-Blue (OOTB) chunk but before
  incrementing the “dropped because of missing route” SNMP statistic, a Null
  Pointer Dereference kernel panic previously occurred. This update fixes the
  race condition between OOTB response and route removal. (BZ#1281426)

• The cpuscaling test of the certification test suite previously failed due
  to a rounding bug in the intel-pstate driver. This bug has been fixed and
  the cpuscaling test now passes. (BZ#1281491)

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.