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Some Intel Tiger Lake-UP3/UP4 CPU models (TGL, family 6, model 140, stepping 1)
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had reports of system hangs when a microcode update, that was included
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since microcode-20201110 update, was applied[1]. In order to address this,
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microcode update had been disabled by default on these systems. The revision
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0x88 seems to have fixed the aforementioned issue, hence it is enabled
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by default (but can be disabled explicitly; see below).
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[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/44
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For the reference, SHA1 checksums of 06-8c-01 microcode files containing
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microcode revisions in question are listed below:
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* 06-8c-01, revision 0x68: 2204a6dee1688980cd228268fdf4b6ed5904fe04
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* 06-8c-01, revision 0x88: 61b6590feb2769046d5b0c394179beaf2df51290
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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-2020-8695 (Information disclosure issue in Intel SGX via RAPL interface),
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CVE-2020-8696 (Vector Register Leakage-Active),
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CVE-2020-8698 (Fast Forward Store Predictor):
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https://access.redhat.com/articles/5569051
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* CVE-2020-24489 (VT-d-related Privilege Escalation),
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CVE-2020-24511 (Improper Isolation of Shared Resources),
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CVE-2020-24512 (Observable Timing Discrepancy),
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CVE-2020-24513 (Information Disclosure on Some Intel Atom Processors):
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https://access.redhat.com/articles/6101171
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The information regarding disabling microcode update is provided below.
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To disable 06-8c-01 microcode updates for a specific kernel
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version, please create a file "disallow-intel-06-8c-01" inside
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/lib/firmware/<kernel_version> directory, run
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"/usr/libexec/microcode_ctl/update_ucode" to remove it from the firmware
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directory where microcode is 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, for example:
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touch /lib/firmware/3.10.0-862.9.1/disallow-intel-06-8c-01
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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 this microcode for all kernels, please create file
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"/etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-8c-01", 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-06-8c-01
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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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