The kernel packages contain the Linux kernel, the core of any Linux operating system. This update includes backported fixes for two security issues. These issues only affected users of Red Hat Enterprise Linux 5.6 Extended Update Support, as they have already been addressed for users of Red Hat Enterprise Linux 5 in the 5.7 update, RHSA-2011:1065. This update fixes the following security issues: * A flaw was found in the way the Xen hypervisor implementation handled instruction emulation during virtual machine exits. A malicious user-space process running in an SMP guest could trick the emulator into reading a different instruction than the one that caused the virtual machine to exit. An unprivileged guest user could trigger this flaw to crash the host. This only affects systems with both an AMD x86 processor and the AMD Virtualization extensions enabled. * A flaw allowed the tc_fill_qdisc function in the Linux kernel"s packet scheduler API implementation to be called on built-in qdisc structures. A local, unprivileged user could use this flaw to trigger a NULL pointer dereference, resulting in a denial of service. This update also fixes the following bugs: * A bug was found in the way the x86_emulate function handled the IMUL instruction in the Xen hypervisor. On systems without support for hardware assisted paging , such as those running CPUs that do not have support for Intel Extended Page Tables or AMD Virtualization Rapid Virtualization Indexing , this bug could cause fully-virtualized guests to crash or lead to silent memory corruption. In reported cases, this issue occurred when booting fully-virtualized Red Hat Enterprise Linux 6.1 guests with memory cgroups enabled. * A bug in the way the ibmvscsi driver handled interrupts may have prevented automatic path recovery for multipath devices. This bug only affected 64-bit PowerPC systems. * The RHSA-2009:1243 update introduced a regression in the way file locking on NFS was handled. This caused applications to hang if they made a lock request on a file on an NFS version 2 or 3 file system that was mounted with the "sec=krb5" option. With this update, the original behavior of using mixed RPC authentication flavors for NFS and locking requests has been restored. Users should upgrade to these updated packages, which contain backported patches to resolve these issues. The system must be rebooted for this update to take effect.