The microcode_ctl package contains microcode files (vendor-provided binary data
and/or code in proprietary format that affects behaviour of a device) for Intel
CPUs that may be loaded into the CPU during boot.
The microcode_ctl package contains provisions for some issues related
to microcode loading. While those provisions are expected to suit most users,
several knobs are available in order to provide ability to override the default
behaviour.
General behaviour
=================
In RHEL 8 (as well as RHEL 7 before it), there are currently two main handlers
for CPU microcode update:
* Early microcode update. It uses GenuineIntel.bin or AuthenticAMD.bin file
placed at the beginning of an initramfs image
(/boot/initramfs-KERNEL_VERSION.img, where "KERNEL_VERSION" is a kernel
version in the same format as provided by "uname -r") as a source
of microcode data, and is performed very early during the boot process
(if the relevant microcode file is available in the aforementioned file).
* On-demand (late) microcode update. It can be triggered by writing "1" to
/sys/devices/system/cpu/microcode/reload file (provided my the "microcode"
module). It relies on request_firmware infrastructure, which searches (and
loads, if found) microcode from a file present in one of the following
directories (in the search order):
/lib/firmware/updates/KERNEL_VERSION/
/lib/firmware/updates/
/lib/firmware/KERNEL_VERSION/
/lib/firmware/
(there is also an additional directory that can be configured via the
"fw_path_para" module option of the "firmware_class" module; as this module
is built-in in RHEL kernel, a boot parameter "firmware_class.fw_path_para"
should be used for that purpose; this is out of the document's scope, however)
The firmware for Intel CPUs is searched in "intel-ucode" subdirectory, and for
AMD CPUs, a file under "amd-ucode" is searched.
For Intel CPUs, the name of the specific microcode file the kernel tries to load
has the format "FF-MM-SS", where "FF" is the family number, "MM" is the model
number, and "SS" is the stepping. All those numbers are zero-filled to two digits
and are written in hexadecimal (letters are in the lower case). For AMD CPUs,
the file name has the format "microcode_amd_famFFh.bin", where "FF" is the
family number, written in hexadecimal, letters are in the lower case, not
zero-filled.
The early microcode is placed into initramfs image by the "dracut" script, which
scans the aforementioned subdirectories of the configured list of firmware
directories (by default, the list consists of two directories in RHEL 8,
"/lib/firmware/updates" and "/lib/firmware").
In RHEL 8, AMD CPU microcode is shipped as a part of the linux-firmware package,
and Intel microcode is shipped as a part of the microcode_ctl package.
The microcode_ctl package currently includes the following:
* Intel CPU microcode files, placed in /usr/share/microcode_ctl/intel-ucode
directory (currently there are none);
* A dracut module, /usr/lib/dracut/modules.d/99microcode_ctl-fw_dir_override,
that controls which additional firmware directories will be added to dracut's
default configuration;
* A dracut configuration file, /usr/lib/dracut/dracut.conf.d/01-microcode.conf,
that enables inclusion of early microcode to the generated initramfs
in dracut;
* A dracut configuration file,
/usr/lib/dracut/dracut.conf.d/99-microcode-override.conf, that provides a way
to quickly disable 99microcode_ctl-fw_dir-override dracut module;
* A systemd service file, microcode.service, that triggers microcode reload
late during boot;
* A set of directories in /usr/share/microcode_ctl/ucode_with_caveats, each
of which contains configuration and related data for various caveats related
to microcode:
* readme - description of caveat and related information,
* config - caveat configuration file, with syntax as described in "Caveat
configuration" section below,
* intel-ucode - directory containing microcode files related to the caveat;
* A set of support scripts, placed in /usr/libexec/microcode_ctl:
* "check_caveats" is an utility script that performs checks of the target
kernel (and running CPU) in accordance with caveat configuration files
in ucode_with_caveats directory and reports whether it passes them or not,
* "reload_microcode" is a script that is called by microcode.service and
triggers microcode reloading (by writing "1" to
/sys/devices/system/cpu/microcode/reload) if the running kernel passes
check_caveats checks,
* "update_ucode" is a script that populates symlinks to microcode files
in /lib/firmware, so it can be picked up by relevant kernels for the late
microcode loading.
Also, microcode_ctl RPM includes triggers that run update_ucode script on every
installation or removal of a kernel RPM in order to provide microcode files
for newly installed kernels and cleanup symlinks for the uninstalled ones.
Caveat configuration
--------------------
There is a directory for each caveat under
/usr/share/microcode_ctl/ucode_with_caveats, containing the following files:
* "config", a configuration file for the caveat;
* "readme", that contains description of the caveat;
* set of related associated microcode files.
"config" file is a set of lines each containing option name and its value,
separated by white space. Currently, the following options are supported:
* "model" option, which has format "VENDOR_ID FF-MM-SS", that specifies
to which CPU model the caveat is applicable (check_caveats ignores caveats
with non-matching models if "-m" option is passed to it). Can be set
in the configuration file only once (the last provided value is used).
* "vendor" option specifies CPUs of which vendor (as provided
in the /proc/cpuinfo file) the caveat is applicable to (check_caveats
ignores caveats with non-matching models when it is invoked with "-m"
option). Can be set in the configuration file only once.
* "path" is a glob pattern that specifies set of microcode files associated
with the caveat as a relative path to the caveat directory. This option
is used for populating files in /lib/firmware by update_ucode script and
for matching microcode file when dracut is run in host-only mode
(as in that case it uses only the first directory in firmware directory list
to look for the microcode file applicable to the host CPU). Can be set
in the configuration file multiple times.
* "kernel" is a minimal kernel version that supports proper handling
of the related microcode files during late microcode load. It may be
provided in one of the following formats that affect the way it is compared
to the running kernel version:
* A.B.C (where A, B, and C are decimal numbers), "upstream version". In this
case, simple version comparison against the respective part of the running
kernel version is used, and the running kernel version should be greater
or equal than the version provided in the configuration option in order
for comparison to succeed (that is, the first part, major version number,
of the running kernel version should be greater than the value provided
in the configuration option, or those should be equal and the second part,
minor version number, should be greater than the minor version number
of the kernel version provided in the configuration option, or the first
two parts should be equal and the third part, patch level, should
be greater or equal the patch level of the version in the configuration
option).
* A.B.C-Y (where A, B, C, and Y are decimal numbers), "Y-stream version".
In this case, A.B.C part should be equal, and Y part of the running kernel
version should be greater or equal than the Y part of the configuration
option version in order to satisfy the comparison requirement.
* A.B.C-Y.Z1.Z2 (where A, B, C, Y, Z1, and Z2 are decimal numbers),
"Z-stream version". In this case, A.B.C-Y part should be equal and Z1.Z2
part of the running kernel should be greater or equal than the respective
part of the configuration option version (when compared as a version)
for comparison to succeed.
Kernel version check passed if at least one comparison of the running kernel
version against a kernel version provided in a configuration option
succeeded. The "kernel" configuration option can be provided
in the configuration file multiple times.
* "kernel_early" is a minimal kernel version that supports proper handling
of the related microcode during early microcode load. The format of the
option and its semantics is similar to the "kernel" configuration options.
This option can be provided multiple times as well.
* "mc_min_ver_late" is the minimal version of the currently loaded microcode
on the CPU (as reported in /proc/cpuinfo) that supports late microcode
update. Microcode update will be attempted only if the currently loaded
microcode version is greater or equal the microcode version provided
in the configuration option. Can be set in the configuration file only once.
* "disable" is a way to disable a specific caveat from inside its
configuration. Argument for the argument is a list of stages ("early",
"late") for which the caveat should be disable. The configuration option
can be provided multiple times in a configuration file.
* "blacklist" is a marker for a start of list of blacklisted model names,
one model name per line. The model name of the running CPU (as reported
in /proc/cpuinfo) is compared against the names in the provided list, and,
if there is a match, caveat check fails.
* "pci_config_val" performs check for specific values in selected parts
of configuration space of specified PCI devices. If "-m" option
is not specified, then the actual check is skipped, and the check returns
result in accordance with the provided "mode" option (se below). Check
arguments are a white-space-separated list of "key=value" pairs.
The following keys are supported:
* "domain" - PCI domain number, or "*" (an asterisk) for any domain.
Default is "*".
* "bus" - PCI bus number, or "*" (an asterisk) for any bus. Default is "*".
* "device" - PCI device number, or "*" (an asterisk) for any device.
Default is "*".
* "function" - PCI function number, or "*" (an asterisk) for any function.
Default is "*".
* "vid" - PCI vendor ID, or empty string for any vendor ID. Default
is empty string.
* "did" - PCI device ID, or empty string for any device ID. Default
is empty string.
* "offset" - offset in device's configuration space where the value resides.
Default is 0.
* "size" - field size. Possible values are 1, 2, 4, or 8. Default is 4.
* "mask" - mask applied to the values during the check. Default is 0.
* "val" - comma-separated list of matching values. Default is 0.
* "mode" - check mode, the way matches are interpreted:
* "success-any" - check succeeds if there was at least one match,
otherwise it fails.
* "success-all" - check succeeds if there was at least one device checked
and all the checked devices have matches, otherwise the check fails.
* "fail-any" - check fails if there was at least one match, otherwise
it succeeds.
* "fail-all" - check fails if there was at least one device checked
and all the checked devices have matches, otherwise the check succeeds.
Default is "success-any".
An example of a check:
pci_config_val mode=success-all device=30 function=3 vid=0x8086 did=0x2083 offset=0x84 size=4 mask=0x38 val=0x38,0x18,0x8
It interprets 4 bytes at offset 0x84 of special files "config" under
directories that match glob pattern "/sys/bus/pci/devices/*:*:1e.3"
as an unsigned integer value, applies mask 0x38 (thus selecting bit 5..3
of it) and checks whether it is one of the values 0x38, 0x18, or 0x8 (0b111,
0b011, or 0b001 in bits 5..3, respectively); if there are such files,
and all the checked values in every checked file has matched at least one
of the aforementioned value, then the check is successful, otherwise
it fails (in accordance with "mode=success-all" semantics). This check fails
if "-m" option is not specified.
* "dmi" performs checks for specific values available in DMI sysfs files
(present under /sys/devices/virtual/dmi/id/). The check fails if file
is not readable. If "-m" option is specified, then the actual check
is skipped, and the check returns value in accordance with "no-model-mode"
parameter value (see below). Check arguments are a white-space-separated
list of "key=value" pairs. The following keys are supported:
* "key" - DMI file to check. Value can be one of the following: bios_date,
bios_vendor, bios_version, board_asset_tag, board_name, board_serial,
board_vendor, board_version, chassis_asset_tag, chassis_serial,
chassis_type, chassis_vendor, chassis_version, product_family,
product_name, product_serial, product_uuid, product_version, sys_vendor.
Default is empty string.
* "val" - a string to match DMI data against. Can be enclosed in single
or double quotes. Default is empty string.
* "mode" - check mode, the way matches are interpreted:
* "success-equal" - returns 0 if the value present in the file
with the name supplied via the "key" parameter file under
/sys/devices/virtual/dmi/id/ is equal to the value supplied as a value
of "val" parameter, otherwise 1.
* "success-equal" - returns 1 if the value present in the file
with the name supplied via the "key" parameter file under
/sys/devices/virtual/dmi/id/ is equal to the value supplied as a value
of "val" parameter, otherwise 0.
Default is "success-any".
* "no-model-mode" - return value if model filter ("-m" option)
is not enabled:
* "success" - return 0.
* "fail" - return 1.
Default is "success".
An example of a check:
dmi mode=fail-equal no-model-mode=success key=bios_vendor val="Dell Inc."
It checks file /sys/devices/virtual/dmi/id/bios_vendor and fails if its
content is "Dell Inc." (without quotes). It succeeds if "-m" option
is not enabled.
check_caveats script
--------------------
"check_caveats" is an utility script (called by update_ucode, reload_microcode,
dracut module) that performs checks of the target kernel (and running CPU)
in accordance with caveat configuration files in directory
"/usr/share/microcode_ctl/ucode_with_caveats", and returns information, whether
the system passes the checks, or not.
Usage:
check_caveats [-e] [-k TARGET_KVER] [-c CONFIG]* [-m] [-v]'
Options:
-e - check for early microcode load possibility (instead of late microcode
load). "kernel_early" caveat configuration options are used for checking
instead of "kernel", and "mc_min_ver_late" is not checked.
-k - target kernel version to check against, $(uname -r) is used otherwise.
-c - caveat(s) to check, all caveat configurations found inside
$MC_CAVEATS_DATA_DIR are checked otherwise.
-m - ignore caveats that do not apply to the current CPU model.
-v - verbose output.
Environment:
MC_CAVEATS_DATA_DIR - directory that contains caveats configurations,
"/usr/share/microcode_ctl/ucode_with_caveats"
by default.
FW_DIR - directory containing firmware files (per-kernel configuration
overrides are checked there), "/lib/firmware" by default.
CFG_DIR - directory containing global caveats overrides,
"/etc/microcode_ctl/ucode_with_caveats" by default.
Output:
Script returns information about caveats check results. Output has a format
of "KEY VALUE1 VALUE2 ..." with KEY defining the semantics of the VALUEs.
Currently, the following data is issued:
- "cfgs" - list of caveats that have been processed (and not skipped
due to missing "config", "readme", or a disallow-* override described
below);
- "skip_cfgs" - list of caveats that have been skipped (due to missing
config/readme file, or because of overrides);
- "paths" - list of glob patterns matching files associated with caveats
that have been processed;
- "ok_cfgs" - list of caveat configurations that have all the checks passed
(or have enforced by one of force-* overrides described below);
- "ok_paths" - list of glob patterns associated with caveat files from
the "ok_cfgs" list;
- "fail_cfgs" - list of caveats that have one of the checks failed.
- "fail_paths" - list of glob patterns associated with caveats from the
"fail_cfgs" list.
Return value:
- 0 in case caveats check has passed, 1 otherwise.
- In "-d" mode, 0 is always returned.
Overrides:
When check_caveats perform its checks, it also checks for presence of files
in specific places, and, if they exist, check_caveats skips a caveat or ignores
its checks; that mechanism allows overriding the information provided
in configuration on local systems and affect the behaviour of the microcode
update process.
Current list of overrides (where $FW_DIR and $CFG_DIR are the environment
options described earlier; $kver - the currently processed kernel version,
$s is the requested stage ("early" or "late"), $cfg is the caveat directory
name):
$FW_DIR/$kver/disallow-$s-$cfg - skip a caveat for the requested stage for
a specific kernel version..
$FW_DIR/$kver/force-$s-$cfg - apply a specific caveat file for a specific
kernel version for the requested stage without
performing any checks.
$FW_DIR/$kver/disallow-$cfg - skip a caveat for any stage for a specific
kernel version.
$FW_DIR/$kver/force-$cfg - apply a specific caveat for any stage
for a specific kernel version without checks.
$FW_DIR/$kver/disallow-$s - skip all caveats for a specific stage
for a specific kernel version.
$CFG_DIR/disallow-$s-$cfg - skip a caveat for a specific stage for all
kernel versions.
$FW_DIR/$kver/force-$s - apply all caveats for a specific stage
for a specific kernel version without checks.
$CFG_DIR/force-$s-$cfg - apply a specific caveat for a specific stage for
all kernel versions without checks.
$FW_DIR/$kver/disallow - skip all caveats for all stages for a specific
kernel version.
$CFG_DIR/disallow-$cfg - skip a caveat for all stages for all kernel
versions.
$FW_DIR/$kver/force - apply all caveats for all stages for a specific kernel
version without checks.
$CFG_DIR/force-$cfg - apply a caveat for all stages for all kernel versions
without checks.
$CFG_DIR/disallow-$s - skip all caveat for all kernel versions
for a specific stage.
$CFG_DIR/force-$s - apply all caveats for all kernel versions for specific
stage without checks.
$CFG_DIR/disallow - skip all caveats for all stages for all kernel versions
(disable everything).
$CFG_DIR/force - force all caveats for all stages for all kernel versions
(enable everything).
The "apply" action above means creating symlinks in /lib/firmware by
update_ucode in case of the "late" stage and adding caveat directory to the list
of firmware directories by dracut plugin in case of the "early" stage.
The files are checked for existence until the first match, so more specific
overrides can override more broad ones.
Also, a caveat is ignored if it lacks either config or readme file.
update_ucode script
-------------------
"update_ucode" populates symlinks to microcode files in accordance with caveats
configuration. It enables late microcode loading that is invoked by triggering
/sys/devices/system/cpu/microcode/reload file. Since caveats depend
on the kernel version, symlinks are populated inside
"/lib/firmware/KERNEL_VERSION" directory for each installed kernel.
As a consequence, this script is triggered upon each kernel package installation
and removal.
The script has two parts: common and kernel-version-specific.
During the common part, files are populated from
/usr/share/microcode_ctl/intel-ucode in /lib/firmware/intel-ucode. There are
several possibilities to affect the process:
* Presence of "/etc/microcode_ctl/intel-ucode-disallow" file leads to skipping
the common part of the script.
* The same for "/lib/firmware/intel-ucode-disallow".
During the kernel-version-specific part, each caveat is checked against every
kernel version, and those combinations, for which caveat check succeeds,
gets the symlinks to the associated microcode files populated.
* Absence of "/lib/firmware/KERNEL_VERSION/readme-CAVEAT" prevents update_ucode
from removing symlinks related to the caveat for specific kernel version.
* Since the check is being done by check_caveats, all the overrides that
described there also stay.
Usage:
update_ucode [--action {add|remove|refresh|list}] [--kernel KERNELVER]*
[--verbose] [--dry-run] [--cleanup intel_ucode caveats_ucode]
[--skip-common] [--skip-kernel-specific]
Options:
--action - action to perform. Currently, the following actions are supported:
* "add" - create new symlinks.
* "remove" - remove old symlinks that are no longer needed.
* "refresh" - re-populate symlinks.
* "list" - list files under control of update_ucode.
By default, "refresh" action is executed.
--kernel - kernel version to process. By default, list of kernel versions
is formed based on contents of /lib/firmware and /lib/modules
directories.
--verbose - verbose output.
--dry-run - do not call commands, just print the invocation lines.
--cleanup - cleanup mode. Used by post-uninstall script during package
upgrades. Removes excess files in accordance to the contents
of the files provided in the arguments to the option.
--skip-common - do not process /lib/firmware directory.
--skip-kernel-specific - do not process /lib/firmware/KERNEL_VERSION
directories.
Return value:
0 on success, 1 on error.
reload_microcode script
-----------------------
"reload_microcode" is a script that is called by microcode.service and
triggers late microcode reloading (by writing "1" to
/sys/devices/system/cpu/microcode/reload) if the following check are passed:
* the microcode update performed not in a virtualised environment;
* running kernel passes "check_caveats" checks that applicable to the current
CPU model.
For a virtualised environment check, the script searches the "/proc/cpuinfo"
file for presence of the "hypervisor" flag among CPU features (it corresponds
to a CPUID feature bit set by hypervisors in order to inform that the kernel
operates inside a virtual machine). This check can be overridden and skipped
by creation of a file "/etc/microcode_ctl/ignore-hypervisor-flag".
The script has no options and always returns 0.
99microcode_ctl-fw_dir_override dracut module
---------------------------------------------
This dracut module injects directories with microcode files for caveats
that pass "early" check_caveats check (with "-e" flag). In addition
to "check_caveats" overrides, the following abilities to control module's
behaviour are present:
* Presence of one of the following files:
- /etc/microcode_ctl/ucode_with_caveats/skip-host-only-check
- /etc/microcode_ctl/ucode_with_caveats/skip-host-only-check-$cfg
- /lib/firmware/$kver/skip-host-only-check
- /lib/firmware/$kver/skip-host-only-check-$cfg
(where "$kver" is the kernel version in question and "$cfg" is the caveat
directory name) allows skipping matching of microcode file name when dracut's
Host-Only mode is enabled.
When caveats_check succeeds, caveats directory (not its possibly populated
version for late microcode update: "/lib/firmware/KERNEL_VERSION";
it is done so in order
to have ability to configure list of caveats enabled for early and late
microcode update, independently) is added to dracut's list of firmware search
directories.
The module can be disabled by running dracut with
"-o microcode_ctl-fw_dir_override" (for one-time exclusion), or it can
be disabled permanently by uncommenting string
"omit_dracutmodules+=' microcode_ctl-fw_dir_override '" in
/usr/lib/dracut/dracut.conf.d/99-microcode-override.conf configuration file.
See dracut(8), section "Omitting dracut Modules", and dracut.conf(5), variable
"omit_dracutmodules" for additional information.
Caveats
=======
Intel Broadwell-EP/EX ("BDX-ML B/M/R0") caveat
----------------------------------------------
Microcode update process on Intel Broadwell-EP/EX CPUs (BDX-ML B/M/R0,
family 6, model 79, stepping 1) has issues that lead to system instability.
A series of changes for the Linux kernel has been developed in order to work
around those issues; however, as it turned out, some systems have issues even
when a microcode update performed on a kernel that contains those changes.
As a result, microcode update for this CPU model is disabled by default;
the microcode file, however, is still shipped as a part of microcode_ctl
package and can be used for performing a microcode update if it is enforced
via the aforementioned overrides. (See the sections "check_caveats script"
and "reload_microcode script" for details.)
Caveat name: intel-06-4f-01
Affected microcode: intel-ucode/06-4f-01.
Mitigation: microcode loading is disabled for the affected CPU model.
Minimum versions of the kernel package that contain the aforementioned patch
series:
- Upstream/RHEL 8: 4.17.0
- RHEL 7.6 onwards: 3.10.0-894
- RHEL 7.5: 3.10.0-862.6.1
- RHEL 7.4: 3.10.0-693.35.1
- RHEL 7.3: 3.10.0-514.52.1
- RHEL 7.2: 3.10.0-327.70.1
- RHEL 6.10: 2.6.32-754.1.1
- RHEL 6.7: 2.6.32-573.58.1
- RHEL 6.6: 2.6.32-504.71.1
- RHEL 6.5: 2.6.32-431.90.1
- RHEL 6.4: 2.6.32-358.90.1
Early microcode load inside a virtual machine
---------------------------------------------
RHEL 8 kernel supports performing microcode update during early boot stage
from a cpio archive placed at the beginning of the initramfs image. However,
when an early microcode update is attempted inside some virtualised
environments, that may result in unexpected system behaviour.
Caveat name: intel
Affected microcode: all.
Mitigation: early microcode loading is disabled for all CPU models on kernels
without the fix.
Minimum versions of the kernel package that contain the fix:
- Upstream/RHEL 8: 4.10.0
- RHEL 7.6 onwards: 3.10.0-930
- RHEL 7.5: 3.10.0-862.14.1
- RHEL 7.4: 3.10.0-693.38.1
- RHEL 7.3: 3.10.0-514.57.1
- RHEL 7.2: 3.10.0-327.73.1
Intel Sandy Bridge-E/EN/EP caveat
---------------------------------
Microcode revision 0x718 for Intel Sandy Bridge-E/EN/EP (SNB-EP, family 6,
model 45, stepping 7), that was released to address MDS vulnerability,
and was available from microcode-20190618 up to microcode-20190508 release)
could lead to system instability[1][2]. In order to address this,
this microcode update was not used and the previous microcode revision
was provided instead by default; the microcode file, however, was still shipped
as part of microcode_ctl package and could be used for performing a microcode
update if it is enforced via the aforementioned overrides. With the release
of 0x71a revision of the microcode (as art of microcode-20200520 release)
that aims at fixing the aforementioned stability issue, the latest microcode
revision is again used by default; it is still provided via the caveat
mechanism, hovewer, in order to enable ability to disable it in case such
a need arises. (See the sections "check_caveats script" and "reload_microcode
script" for details regarding caveats mechanism operation.)
[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/15
[2] https://access.redhat.com/solutions/4593951
Caveat name: intel-06-2d-07
Affected microcode: intel-ucode/06-2d-07.
Mitigation: None; the latest revision of the microcode file is used by default;
previously published microcode revision 0x714 is still available as a fallback
as part of "intel" caveat.
Intel Skylake-SP/W/X caveat
---------------------------
Microcode revision 0x2000065 (that was provided with microcode releases
microcode-20191112 up to microcode-20200520) for some CPU models that belong
to Intel Skylake Scalable Platform (SKL-W/X, family 6, model 85, stepping 4,
Workstation/HEDT segments) could lead to hangs during reboot[1]. In order
to address this, by default this microcode update was disabled by default and
and the previous 0x2000064 microcode revision was used instead; the microcode
file with, however, is still shipped as part of microcode_ctl package and can
be used for performing a microcode update if it is enforced
via the aforementioned overrides. With the availability of 0x2006906 revision
of the microcode (in the microcode-20200609 release) that fixes
the aforementioned issue, the latest microcode revision is again used
by default; it is still provided via caveat mechanism, hovewer, in order
to enable ability to disable it in case such a need arises. (See the sections
"check_caveats script" and "reload_microcode script" for details regarding
caveats mechanism operation.)
[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/21
Caveat name: intel-06-55-04
Affected microcode: intel-ucode/06-55-04.
Mitigation: None; the latest revision of the microcode file is used by default;
previously published microcode revision 0x2000064 is still available
as a fallback as part of "intel" caveat.
Intel Skylake-U/Y/H/S/Xeon E3 v5 caveats
----------------------------------------
Some Intel Skylake CPU models (SKL-U/Y, family 6, model 78, stepping 3;
and SKL-H/S/Xeon E3 v5, family 6, model 94, stepping 3) have reports of system
hangs when revision 0xdc of microcode, that is included in microcode-20200609
update to address CVE-2020-0543, CVE-2020-0548, and CVE-2020-0549,
is applied[1][2]. In order to address this, microcode update to the newer
revision has been disabled by default on these systems, and the previously
published microcode revision 0xd6 is used instead; the newer microcode files,
however, are still shipped as part of microcode_ctl package and can be used
for performing a microcode update if they are enforced via the aforementioned
overrides. (See the sections "check_caveats script" and "reload_microcode
script" for details.)
[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/31
[2] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/31#issuecomment-644885826
Caveat names: intel-06-4e-03, intel-06-5e-03
Affected microcode: intel-ucode/06-4e-03, intel-ucode/06-5e-03.
Mitigation: previously published microcode revision 0xd6 is used by default.
Dell caveats
------------
Some Dell systems that use some models of Intel CPUs are susceptible to hangs
and system instability during or after microcode update to revision 0xc6/0xca
(included as part of microcode-20191113/microcode-20191115 update that addressed
CVE-2019-0117, CVE-2019-0123, CVE-2019-11135, and CVE-2019-11139)
and/or revision 0xd6 (included as part of microcode-20200609 update
that addressed CVE-2020-0543, CVE-2020-0548, and CVE-2020-0549)
[1][2][3][4][5][6]. In order to address this, microcode update to the newer
revision has been disabled by default on these systems, and the previously
published microcode revisions 0xae/0xb4/0xb8 are used by default
for the OS-driven microcode update.
[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/23
[2] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/24
[3] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/33
[4] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/34
[5] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/35
[6] https://bugzilla.redhat.com/show_bug.cgi?id=1846097
Caveat names: intel-06-8e-9e-0x-dell, intel-06-8e-9e-0x-0xca
Affected microcode: intel-ucode/06-8e-09, intel-ucode/06-8e-0a,
intel-ucode/06-8e-0b, intel-ucode/06-8e-0c,
intel-ucode/06-9e-09, intel-ucode/06-9e-0a,
intel-ucode/06-9e-0b, intel-ucode/06-9e-0c,
intel-ucode/06-9e-0d.
Mitigation: previously published microcode revision 0xac/0xb4/0xb8 is used
by default if /sys/devices/virtual/dmi/id/bios_vendor reports
"Dell Inc."; otherwise, the latest microcode revision is used.
Caveat with revision 0xca of microcode files is provided
as a convenience for the cases where it was working well before.
Intel Tiger Lake-UP3/UP4 caveat
-------------------------------
Some systems with Intel Tiger Lake-UP3/UP4 CPUs (TGL, family 6, model 140,
stepping 1) have reports of system hangs when a microcode update,
that is included since microcode-20201110 release, is applied[1].
In order to address this, microcode update to a newer revision has been disabled
by default on these systems; the newer microcode file, however, is still shipped
as a part of microcode_ctl package and can be used for performing a microcode
update if it is enforced via the aforementioned overrides. (See the sections
"check_caveats script" and "reload_microcode script" for details.)
[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/issues/44
Caveat names: intel-06-8c-01
Affected microcode: intel-ucode/06-8c-01.
Mitigation: microcode loading is disabled for the affected CPU model.
Additional information
======================
Red Hat provides updated microcode, developed by its microprocessor partners,
as a customer convenience. Please contact your hardware vendor to determine
whether more recent BIOS/firmware updates are recommended because additional
improvements may be available.
Information regarding microcode revisions required for mitigating specific
Intel CPU vulnerabilities is available in the following knowledge base articles:
* CVE-2017-5715 ("Spectre"):
https://access.redhat.com/articles/3436091
* CVE-2018-3639 ("Speculative Store Bypass"):
https://access.redhat.com/articles/3540901
* CVE-2018-3620, CVE-2018-3646 ("L1 Terminal Fault Attack"):
https://access.redhat.com/articles/3562741
* CVE-2018-12130, CVE-2018-12126, CVE-2018-12127, and CVE-2019-11091
("Microarchitectural Data Sampling"):
https://access.redhat.com/articles/4138151
* CVE-2019-0117 (Intel SGX Information Leak),
CVE-2019-0123 (Intel SGX Privilege Escalation),
CVE-2019-11135 (TSX Asynchronous Abort),
CVE-2019-11139 (Voltage Setting Modulation):
https://access.redhat.com/solutions/2019-microcode-nov
* CVE-2020-0543 (Special Register Buffer Data Sampling),
CVE-2020-0548 (Vector Register Data Sampling),
CVE-2020-0549 (L1D Cache Eviction Sampling):
https://access.redhat.com/solutions/5142751
* 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