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Intel Sandy Bridge-E/EN/EP CPU models (SNB-EP, family 6, model 45, stepping 7)
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had issues with MDS-related microcode update that may lead to a system hang
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after a microcode update[1][2]. In order to address this, microcode update
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to the MDS-related revision 0x718 had been disabled, and the previously
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published microcode revision 0x714 is used by default for the OS-driven
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microcode update. The revision 0x71a of the microcode is intended to fix
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the aforementioned issue, hence it is enabled by default (but can be disabled
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explicitly; see below).
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[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/15
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[2] https://access.redhat.com/solutions/4593951
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For the reference, SHA1 checksums of 06-2d-07 microcode files containing
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microcode revisions in question are listed below:
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* 06-2d-07, revision 0x714: bcf2173cd3dd499c37defbc2533703cfa6ec2430
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* 06-2d-07, revision 0x718: 837cfebbfc09b911151dfd179082ad99cf87e85d
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* 06-2d-07, revision 0x71a: 4512c8149e63e5ed15f45005d7fb5be0041f66f6
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Please contact your system vendor for a BIOS/firmware update that contains
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the latest microcode version. For the information regarding microcode versions
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required for mitigating specific side-channel cache attacks, please refer
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to the following knowledge base articles:
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* CVE-2017-5715 ("Spectre"):
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https://access.redhat.com/articles/3436091
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* CVE-2018-3639 ("Speculative Store Bypass"):
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https://access.redhat.com/articles/3540901
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* CVE-2018-3620, CVE-2018-3646 ("L1 Terminal Fault Attack"):
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https://access.redhat.com/articles/3562741
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* CVE-2018-12130, CVE-2018-12126, CVE-2018-12127, and CVE-2019-11091
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("Microarchitectural Data Sampling"):
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https://access.redhat.com/articles/4138151
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The information regarding disabling microcode update is provided below.
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To disable usage of the newer microcode revision for a specific kernel
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version, please create file "disallow-intel-06-2d-07" inside
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/lib/firmware/<kernel_version> directory, run
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"/usr/libexec/microcode_ctl/update_ucode" to add it to firmware directory
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where microcode will be available for late microcode update, and run
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"dracut -f --kver <kernel_version>", so initramfs for this kernel version
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is regenerated and the microcode can be loaded early, for example:
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touch /lib/firmware/3.10.0-862.9.1/disallow-intel-06-2d-07
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/usr/libexec/microcode_ctl/update_ucode
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dracut -f --kver 3.10.0-862.9.1
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To avoid addition of the newer microcode revision for all kernels, please create
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file "/etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-2d-07", run
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"/usr/libexec/microcode_ctl/update_ucode" for late microcode updates,
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and "dracut -f --regenerate-all" for early microcode updates:
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mkdir -p /etc/microcode_ctl/ucode_with_caveats
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touch /etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-2d-07
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/usr/libexec/microcode_ctl/update_ucode
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dracut -f --regenerate-all
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Please refer to /usr/share/doc/microcode_ctl/README.caveats for additional
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information.
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