793 Specific Combination of Writes to Write Combined Memory Types and Locked Instructions May Cause Core Hang Under a highly specific and detailed set of internal timing conditions, a locked instruction may trigger a timing sequence whereby the write to a write combined memory type is not flushed, causing the locked instruction to stall indefinitely. Potential Effect on System Processor core hang. Suggested Workaround BIOS should set MSRC001_1020[15] = 1b. The vulnerability is applicable only to family 16h model 00h-0fh AMD CPUs. Non-AMD CPUs are not vulnerable. References: http://support.amd.com/TechDocs/51810_16h_00h-0Fh_Rev_Guide.pdf http://thread.gmane.org/gmane.comp.security.oss.general/11555 Acknowledgements: Red Hat would like to thank the Xen project for reporting this issue. Upstream acknowledges Jan Beulich as the original reporter.
Statement: This hardware issue is affecting certain AMD processors. Please consult your hardware vendor for any potential firmware updates providing a workaround for this issue.
Xen issued advisory: http://www.openwall.com/lists/oss-security/2013/12/02/1
Linux kernel proposed workaround: http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=3b56496865f9f7d9bcb2f93b44c63f274f08e3b6
It was noted that the previous fix was not sufficient for 32bit systems and also requires the following patch: http://xenbits.xenproject.org/xsa/xsa82-4.1-32bit.patch or http://xenbits.xenproject.org/xsa/xsa82-4.2-32bit.patch The advisory has further details. External References: http://xenbits.xenproject.org/xsa/advisory-82.html
This shouldn't affect our backport. No additional patch needed for rhel5.
This issue has been addressed in following products: Red Hat Enterprise Linux 5 Via RHSA-2014:0285 https://rhn.redhat.com/errata/RHSA-2014-0285.html