What: /sys/class/firmware-attributes/*/attributes/*/
Date: February 2021
KernelVersion: 5.11
Contact: Divya Bharathi <[email protected]>,
Prasanth KSR <[email protected]>
[email protected]
Description:
A sysfs interface for systems management software to enable
configuration capability on supported systems. This directory
exposes interfaces for interacting with configuration options.
Unless otherwise specified in an attribute description all attributes are optional
and will accept UTF-8 input.
type:
A file that can be read to obtain the type of attribute.
This attribute is mandatory.
The following are known types:
- enumeration: a set of pre-defined valid values
- integer: a range of numerical values
- string
HP specific types
-----------------
- ordered-list - a set of ordered list valid values
All attribute types support the following values:
current_value:
A file that can be read to obtain the current
value of the <attr>.
This file can also be written to in order to update the value of a
<attr>
This attribute is mandatory.
default_value:
A file that can be read to obtain the default
value of the <attr>
display_name:
A file that can be read to obtain a user friendly
description of the at <attr>
display_name_language_code:
A file that can be read to obtain
the IETF language tag corresponding to the
"display_name" of the <attr>
"enumeration"-type specific properties:
possible_values:
A file that can be read to obtain the possible
values of the <attr>. Values are separated using
semi-colon (``;``).
"integer"-type specific properties:
min_value:
A file that can be read to obtain the lower
bound value of the <attr>
max_value:
A file that can be read to obtain the upper
bound value of the <attr>
scalar_increment:
A file that can be read to obtain the scalar value used for
increments of current_value this attribute accepts.
"string"-type specific properties:
max_length:
A file that can be read to obtain the maximum
length value of the <attr>
min_length:
A file that can be read to obtain the minimum
length value of the <attr>
Dell specific class extensions
------------------------------
On Dell systems the following additional attributes are available:
dell_modifier:
A file that can be read to obtain attribute-level
dependency rule. It says an attribute X will become read-only or
suppressed, if/if-not attribute Y is configured.
modifier rules can be in following format::
[ReadOnlyIf:<attribute>=<value>]
[ReadOnlyIfNot:<attribute>=<value>]
[SuppressIf:<attribute>=<value>]
[SuppressIfNot:<attribute>=<value>]
For example::
AutoOnFri/dell_modifier has value,
[SuppressIfNot:AutoOn=SelectDays]
This means AutoOnFri will be suppressed in BIOS setup if AutoOn
attribute is not "SelectDays" and its value will not be effective
through sysfs until this rule is met.
Enumeration attributes also support the following:
dell_value_modifier:
A file that can be read to obtain value-level dependency.
This file is similar to dell_modifier but here, an
attribute's current value will be forcefully changed based
dependent attributes value.
dell_value_modifier rules can be in following format::
<value>[ForceIf:<attribute>=<value>]
<value>[ForceIfNot:<attribute>=<value>]
For example::
LegacyOrom/dell_value_modifier has value:
Disabled[ForceIf:SecureBoot=Enabled]
This means LegacyOrom's current value will be forced to
"Disabled" in BIOS setup if SecureBoot is Enabled and its
value will not be effective through sysfs until this rule is
met.
HP specific class extensions
------------------------------
On HP systems the following additional attributes are available:
"ordered-list"-type specific properties:
elements:
A file that can be read to obtain the possible
list of values of the <attr>. Values are separated using
semi-colon (``;``) and listed according to their priority.
An element listed first has the highest priority. Writing
the list in a different order to current_value alters
the priority order for the particular attribute.
What: /sys/class/firmware-attributes/*/authentication/
Date: February 2021
KernelVersion: 5.11
Contact: Divya Bharathi <[email protected]>,
Prasanth KSR <[email protected]>
[email protected]
Description:
Devices support various authentication mechanisms which can be exposed
as a separate configuration object.
For example a "BIOS Admin" password and "System" Password can be set,
reset or cleared using these attributes.
- An "Admin" password is used for preventing modification to the BIOS
settings.
- A "System" password is required to boot a machine.
Change in any of these two authentication methods will also generate an
uevent KOBJ_CHANGE.
is_enabled:
A file that can be read to obtain a 0/1 flag to see if
<attr> authentication is enabled.
This attribute is mandatory.
role:
The type of authentication used.
This attribute is mandatory.
Known types:
bios-admin:
Representing BIOS administrator password
power-on:
Representing a password required to use
the system
system-mgmt:
Representing System Management password.
See Lenovo extensions section for details
HDD:
Representing HDD password
See Lenovo extensions section for details
NVMe:
Representing NVMe password
See Lenovo extensions section for details
mechanism:
The means of authentication. This attribute is mandatory.
Only supported type currently is "password".
max_password_length:
A file that can be read to obtain the
maximum length of the Password
min_password_length:
A file that can be read to obtain the
minimum length of the Password
current_password:
A write only value used for privileged access such as
setting attributes when a system or admin password is set
or resetting to a new password
This attribute is mandatory when mechanism == "password".
new_password:
A write only value that when used in tandem with
current_password will reset a system or admin password.
Note, password management is session specific. If Admin password is set,
same password must be written into current_password file (required for
password-validation) and must be cleared once the session is over.
For example::
echo "password" > current_password
echo "disabled" > TouchScreen/current_value
echo "" > current_password
Drivers may emit a CHANGE uevent when a password is set or unset
userspace may check it again.
On Dell, Lenovo and HP systems, if Admin password is set, then all BIOS attributes
require password validation.
On Lenovo systems if you change the Admin password the new password is not active until
the next boot.
Lenovo specific class extensions
--------------------------------
On Lenovo systems the following additional settings are available:
role: system-mgmt This gives the same authority as the bios-admin password to control
security related features. The authorities allocated can be set via
the BIOS menu SMP Access Control Policy
role: HDD & NVMe This password is used to unlock access to the drive at boot. Note see
'level' and 'index' extensions below.
lenovo_encoding:
The encoding method that is used. This can be either "ascii"
or "scancode". Default is set to "ascii"
lenovo_kbdlang:
The keyboard language method that is used. This is generally a
two char code (e.g. "us", "fr", "gr") and may vary per platform.
Default is set to "us"
level:
Available for HDD and NVMe authentication to set 'user' or 'master'
privilege level.
If only the user password is configured then this should be used to
unlock the drive at boot. If both master and user passwords are set
then either can be used. If a master password is set a user password
is required.
This attribute defaults to 'user' level
index:
Used with HDD and NVME authentication to set the drive index
that is being referenced (e.g hdd1, hdd2 etc)
This attribute defaults to device 1.
certificate, signature, save_signature:
These attributes are used for certificate based authentication. This is
used in conjunction with a signing server as an alternative to password
based authentication.
The user writes to the attribute(s) with a BASE64 encoded string obtained
from the signing server.
The attributes can be displayed to check the stored value.
Some usage examples:
Installing a certificate to enable feature::
echo "supervisor password" > authentication/Admin/current_password
echo "signed certificate" > authentication/Admin/certificate
Updating the installed certificate::
echo "signature" > authentication/Admin/signature
echo "signed certificate" > authentication/Admin/certificate
Removing the installed certificate::
echo "signature" > authentication/Admin/signature
echo "" > authentication/Admin/certificate
Changing a BIOS setting::
echo "signature" > authentication/Admin/signature
echo "save signature" > authentication/Admin/save_signature
echo Enable > attribute/PasswordBeep/current_value
You cannot enable certificate authentication if a supervisor password
has not been set.
Clearing the certificate results in no bios-admin authentication method
being configured allowing anyone to make changes.
After any of these operations the system must reboot for the changes to
take effect.
certificate_thumbprint:
Read only attribute used to display the MD5, SHA1 and SHA256 thumbprints
for the certificate installed in the BIOS.
certificate_to_password:
Write only attribute used to switch from certificate based authentication
back to password based.
Usage::
echo "signature" > authentication/Admin/signature
echo "password" > authentication/Admin/certificate_to_password
HP specific class extensions
--------------------------------
On HP systems the following additional settings are available:
role: enhanced-bios-auth:
This role is specific to Secure Platform Management (SPM) attribute.
It requires configuring an endorsement (kek) and signing certificate (sk).
What: /sys/class/firmware-attributes/*/attributes/pending_reboot
Date: February 2021
KernelVersion: 5.11
Contact: Divya Bharathi <[email protected]>,
Prasanth KSR <[email protected]>
[email protected]
Description:
A read-only attribute reads 1 if a reboot is necessary to apply
pending BIOS attribute changes. Also, an uevent_KOBJ_CHANGE is
generated when it changes to 1.
== =========================================
0 All BIOS attributes setting are current
1 A reboot is necessary to get pending BIOS
attribute changes applied
== =========================================
Note, userspace applications need to follow below steps for efficient
BIOS management,
1. Check if admin password is set. If yes, follow session method for
password management as briefed under authentication section above.
2. Before setting any attribute, check if it has any modifiers
or value_modifiers. If yes, incorporate them and then modify
attribute.
Drivers may emit a CHANGE uevent when this value changes and userspace
may check it again.
What: /sys/class/firmware-attributes/*/attributes/reset_bios
Date: February 2021
KernelVersion: 5.11
Contact: Divya Bharathi <[email protected]>,
Prasanth KSR <[email protected]>
[email protected]
Description:
This attribute can be used to reset the BIOS Configuration.
Specifically, it tells which type of reset BIOS configuration is being
requested on the host.
Reading from it returns a list of supported options encoded as:
- 'builtinsafe' (Built in safe configuration profile)
- 'lastknowngood' (Last known good saved configuration profile)
- 'factory' (Default factory settings configuration profile)
- 'custom' (Custom saved configuration profile)
The currently selected option is printed in square brackets as
shown below::
# echo "factory" > /sys/class/firmware-attributes/*/device/attributes/reset_bios
# cat /sys/class/firmware-attributes/*/device/attributes/reset_bios
builtinsafe lastknowngood [factory] custom
Note that any changes to this attribute requires a reboot
for changes to take effect.
What: /sys/class/firmware-attributes/*/attributes/save_settings
Date: August 2023
KernelVersion: 6.6
Contact: Mark Pearson <[email protected]>
Description:
On Lenovo platforms there is a limitation in the number of times an attribute can be
saved. This is an architectural limitation and it limits the number of attributes
that can be modified to 48.
A solution for this is instead of the attribute being saved after every modification,
to allow a user to bulk set the attributes, and then trigger a final save. This allows
unlimited attributes.
Read the attribute to check what save mode is enabled (single or bulk).
E.g:
# cat /sys/class/firmware-attributes/thinklmi/attributes/save_settings
single
Write the attribute with 'bulk' to enable bulk save mode.
Write the attribute with 'single' to enable saving, after every attribute set.
The default setting is single mode.
E.g:
# echo bulk > /sys/class/firmware-attributes/thinklmi/attributes/save_settings
When in bulk mode write 'save' to trigger a save of all currently modified attributes.
Note, once a save has been triggered, in bulk mode, attributes can no longer be set and
will return a permissions error. This is to prevent users hitting the 48+ save limitation
(which requires entering the BIOS to clear the error condition)
E.g:
# echo save > /sys/class/firmware-attributes/thinklmi/attributes/save_settings
What: /sys/class/firmware-attributes/*/attributes/debug_cmd
Date: July 2021
KernelVersion: 5.14
Contact: Mark Pearson <[email protected]>
Description:
This write only attribute can be used to send debug commands to the BIOS.
This should only be used when recommended by the BIOS vendor. Vendors may
use it to enable extra debug attributes or BIOS features for testing purposes.
Note that any changes to this attribute requires a reboot for changes to take effect.
HP specific class extensions - Secure Platform Manager (SPM)
--------------------------------
What: /sys/class/firmware-attributes/*/authentication/SPM/kek
Date: March 2023
KernelVersion: 5.18
Contact: "Jorge Lopez" <[email protected]>
Description:
'kek' Key-Encryption-Key is a write-only file that can be used to configure the
RSA public key that will be used by the BIOS to verify
signatures when setting the signing key. When written,
the bytes should correspond to the KEK certificate
(x509 .DER format containing an OU). The size of the
certificate must be less than or equal to 4095 bytes.
What: /sys/class/firmware-attributes/*/authentication/SPM/sk
Date: March 2023
KernelVersion: 5.18
Contact: "Jorge Lopez" <[email protected]>
Description:
'sk' Signature Key is a write-only file that can be used to configure the RSA
public key that will be used by the BIOS to verify signatures
when configuring BIOS settings and security features. When
written, the bytes should correspond to the modulus of the
public key. The exponent is assumed to be 0x10001.
What: /sys/class/firmware-attributes/*/authentication/SPM/status
Date: March 2023
KernelVersion: 5.18
Contact: "Jorge Lopez" <[email protected]>
Description:
'status' is a read-only file that returns ASCII text in JSON format reporting
the status information.
"State": "not provisioned | provisioned | provisioning in progress",
"Version": "Major.Minor",
"Nonce": <16-bit unsigned number display in base 10>,
"FeaturesInUse": <16-bit unsigned number display in base 10>,
"EndorsementKeyMod": "<256 bytes in base64>",
"SigningKeyMod": "<256 bytes in base64>"
What: /sys/class/firmware-attributes/*/attributes/Sure_Start/audit_log_entries
Date: March 2023
KernelVersion: 5.18
Contact: "Jorge Lopez" <[email protected]>
Description:
'audit_log_entries' is a read-only file that returns the events in the log.
Audit log entry format
Byte 0-15: Requested Audit Log entry (Each Audit log is 16 bytes)
Byte 16-127: Unused
What: /sys/class/firmware-attributes/*/attributes/Sure_Start/audit_log_entry_count
Date: March 2023
KernelVersion: 5.18
Contact: "Jorge Lopez" <[email protected]>
Description:
'audit_log_entry_count' is a read-only file that returns the number of existing
audit log events available to be read. Values are separated using comma. (``,``)
[No of entries],[log entry size],[Max number of entries supported]
log entry size identifies audit log size for the current BIOS version.
The current size is 16 bytes but it can be up to 128 bytes long in future BIOS
versions.
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