RHEL 5: RHSA-2009:1659-01 Moderate: KVM Denial of Service Fix

KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux on AMD64 and Intel 64 systems. KVM is a Linux kernel module built for the standard Red Hat Enterprise Linux kernel.
On x86 platforms, the do_insn_fetch() function did not limit the amount of instruction bytes fetched per instruction. Users in guest operating systems could leverage this flaw to cause large latencies on SMP hosts that could lead to a local denial of service on the host operating system. This update fixes this issue by imposing the architecturally-defined 15 byte length limit for instructions. (CVE-2009-4031)
This update also fixes the following bugs:
* performance problems occurred when using the qcow2 image format with the qemu-kvm -drive "cache=none" option (the default setting when not specified otherwise). This could cause guest operating system installations to take hours. With this update, performance patches have been backported so that using the qcow2 image format with the "cache=none" option no longer causes performance issues. (BZ#520693)
* when using the virtual vm8086 mode, bugs in the emulated hardware task switching implementation may have, in some situations, caused older guest operating systems to malfunction. (BZ#532031)
* Windows Server 2003 guests (32-bit) with more than 4GB of memory may have crashed during reboot when using the default qemu-kvm CPU settings. (BZ#532043)
* with Red Hat Enterprise Virtualization, guests continued to run after encountering disk read errors. This could have led to their file systems becoming corrupted (but not the host's), notably in environments that use networked storage. With this update, the qemu-kvm -drive "werror=stop" option now applies not only to write errors but also to read errors: When using this option, guests will pause on disk read and write errors.
By default, guests managed by Red Hat Enterprise Virtualization use the "werror=stop" option. This option is not used by default for guests managed by libvirt. (BZ#537334, BZ#540406)
* the para-virtualized block driver (virtio-blk) silently ignored read errors when accessing disk images. With this update, the driver correctly signals the read error to the guest. (BZ#537334)
All KVM users should upgrade to these updated packages, which contain backported patches to resolve these issues. Note: The procedure in the Solution section must be performed before this update will take effect.