/usr/share/doc/microcode_ctl/caveats/ Current File: //usr/share/doc/microcode_ctl/caveats/06-8c-01_readme
Some Intel Tiger Lake-UP3/UP4 CPU models (TGL, family 6, model 140, stepping 1)
had reports of system hangs when a microcode update, that was included
since microcode-20201110 update, was applied[1].  In order to address this,
microcode update had been disabled by default on these systems.  The revision
0x88 seems to have fixed the aforementioned issue, hence it is enabled
by default (but can be disabled explicitly; see below).

[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/44

For the reference, SHA1 checksums of 06-8c-01 microcode files containing
microcode revisions in question are listed below:
 * 06-8c-01, revision 0x68: 2204a6dee1688980cd228268fdf4b6ed5904fe04
 * 06-8c-01, revision 0x88: 61b6590feb2769046d5b0c394179beaf2df51290
 * 06-8c-01, revision 0x9a: 48b3ae8d27d8138b5b47052d2f8184bf555ad18e
 * 06-8c-01, revision 0xa4: 70753f54f5be84376bdebeb710595e4dc2f6d92f
 * 06-8c-01, revision 0xa6: fdcf89e3a15a20df8aeee215b78bf5d13d731044
 * 06-8c-01, revision 0xaa: cf84883f6b3184690c25ccade0b10fa839ac8657
 * 06-8c-01, revision 0xac: b9f342e564a0be372ed1f4709263bf811feb022a
 * 06-8c-01, revision 0xb4: 6596bb8696cde85538bb833d090f0b7a42d6ae14

Please contact your system vendor for a BIOS/firmware update that contains
the latest microcode version.  For the information regarding microcode versions
required for mitigating specific side-channel cache attacks, please refer
to the following knowledge base articles:
 * CVE-2020-8695 (Information disclosure issue in Intel SGX via RAPL interface),
   CVE-2020-8696 (Vector Register Leakage-Active),
   CVE-2020-8698 (Fast Forward Store Predictor):
   https://access.redhat.com/articles/5569051
 * CVE-2020-24489 (VT-d-related Privilege Escalation),
   CVE-2020-24511 (Improper Isolation of Shared Resources),
   CVE-2020-24512 (Observable Timing Discrepancy),
   CVE-2020-24513 (Information Disclosure on Some Intel Atom Processors):
   https://access.redhat.com/articles/6101171
 * CVE-2021-0145 (Fast store forward predictor - Cross Domain Training):
   https://access.redhat.com/articles/6716541
 * CVE-2022-21123 (Shared Buffers Data Read):
   https://access.redhat.com/articles/6963124

The information regarding disabling microcode update is provided below.

To disable 06-8c-01 microcode updates for a specific kernel
version, please create a file "disallow-intel-06-8c-01" inside
/lib/firmware/<kernel_version> directory, run
"/usr/libexec/microcode_ctl/update_ucode" to remove it from the firmware
directory where microcode is available for late microcode update, and run
"dracut -f --kver <kernel_version>", so initramfs for this kernel version
is regenerated, for example:

    touch /lib/firmware/3.10.0-862.9.1/disallow-intel-06-8c-01
    /usr/libexec/microcode_ctl/update_ucode
    dracut -f --kver 3.10.0-862.9.1

To avoid addition of this microcode for all kernels, please create file
"/etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-8c-01", run
"/usr/libexec/microcode_ctl/update_ucode" for late microcode updates,
and "dracut -f --regenerate-all" for early microcode updates:

    mkdir -p /etc/microcode_ctl/ucode_with_caveats
    touch /etc/microcode_ctl/ucode_with_caveats/disallow-intel-06-8c-01
    /usr/libexec/microcode_ctl/update_ucode
    dracut -f --regenerate-all

Please refer to /usr/share/doc/microcode_ctl/README.caveats for additional
information.