RHSA-2015:2552: Important: kernel security and bug fix update

The kernel packages contain the Linux kernel, the core of any Linuxoperating 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 ofan infinite loop in the microcode due to the way (sequential) delivering ofbenign exceptions such as #AC (alignment check exception) and #DB (debugexception) is handled. A privileged user inside a guest could use theseflaws 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 theCVE-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 clientplatforms failed. This update sets the idle frequency, busy frequency, andprocessor frequency values by determining the range and adjusting theminimal and maximal percent limit values. Now, switching p-states on theaforementioned 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 EnterpriseVirtualization Hypervisor. The provided patch fixes this bug by droppingthe 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 becomeunresponsive during the hot-unplug operation if a driver was removed.This update fixes the driver memory leak bug on command retries, and thekernel no longer hangs in this situation. (BZ#1279792) The hybriddmadata() function was not initialized before use, which caused an invalid memory access when hot-plugging a PCI card. As aconsequence, a kernel oops occurred. The provided patch makes surehybriddmadata() is initialized before use, and the kernel oops no longeroccurs 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 hostsometimes triggered an incorrect kind of interrupt in the guest: a datastorage exception instead of a data segment exception. This caused a kernelpanic of the PPC KVM guest. With this update, the host kernel synthesizes asegment fault if the corresponding Segment Lookaside Buffer (SLB) lookupfails, 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 inmedlp5. The backported upstream patch prevents an LPAR hang, and the oopsno 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 beforeincrementing the "dropped because of missing route" SNMP statistic, a NullPointer Dereference kernel panic previously occurred. This update fixes therace 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 andthe cpuscaling test now passes. (BZ#1281491)All kernel users are advised to upgrade to these updated packages, whichcontain backported patches to correct these issues. The system must berebooted for this update to take effect.