4.9 - RHSA-2015:2552

Problem Description:

Updated kernel packages that fix two security issues, several bugs, and add one enhancement are now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having Important security impact. Common Vulnerability Scoring System (CVSS) base scores, which give detailed severity ratings, are available for each vulnerability from the CVE links in the References section.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Client (v. 7) - noarch, x86_64 Red Hat Enterprise Linux Client Optional (v. 7) - x86_64 Red Hat Enterprise Linux ComputeNode (v. 7) - noarch, x86_64 Red Hat Enterprise Linux ComputeNode Optional (v. 7) - x86_64 Red Hat Enterprise Linux Server (v. 7) - noarch, ppc64, ppc64le, s390x, x86_64 Red Hat Enterprise Linux Server Optional (v. 7) - ppc64, ppc64le, x86_64 Red Hat Enterprise Linux Workstation (v. 7) - noarch, x86_64 Red Hat Enterprise Linux Workstation Optional (v. 7) - x86_64

3. Description:

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.

4. Solution:

Before applying this update, make sure all previously released errata relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258

5. Bugs fixed (https://bugzilla.redhat.com/):

1277172 - CVE-2015-5307 virt: guest to host DoS by triggering an infinite loop in microcode via #AC exception 1278496 - CVE-2015-8104 virt: guest to host DoS by triggering an infinite loop in microcode via #DB exception