Hi, On 3/15/22 20:56, Mark Pearson wrote: > Certificate based authentication is available as an alternative to > password based authentication. > > The WMI commands are cryptographically signed using a separate > signing server and will be verified by the BIOS before being > accepted. > > This commit details the fields that are needed to support that > implementation. At present the changes are intended for Lenovo > platforms, but have been designed to keep them as flexible as possible > for future implementations from other vendors. > > Signed-off-by: Mark Pearson <markpearson@xxxxxxxxxx> This looks good, but looking at this a second time I still have one open question: What is the difference between removing a certificate and switching back to password auth? Looking at the WMI calls there are 4 different calls: LENOVO_SET_BIOS_CERT_GUID LENOVO_UPDATE_BIOS_CERT_GUID LENOVO_CLEAR_BIOS_CERT_GUI LENOVO_CERT_TO_PASSWORD_GUID Going by these names I guess there can be only 1 certificate otherwise I would expect: 1. add/remove naming 2. update to take an id of which certificate to replace So I guess that LENOVO_CLEAR_BIOS_CERT_GUI disables all authentication. IOW, installing a cert replaces/clears the supervisor password and the difference between clearing the certificate and cert-to-password is that after clearing it we end up with no supervisor password set, where as cert-to-password sets the passed in password as the new supervisor password? Or does clearing the certificate fall back to the old supervisor password if one was set? (that might lead to some interesting issues if users clear the certificate many years after the password was last used ...) Given where we are in the cycle I was planning on adding this to my review-hans branch so that it could maybe still get into 5.18, but given the above questions as well the remark about the test X1 BIOS you are using I've a feeling it would be better to give this some more time to bake and target 5.19 instead. Do you agree ? Regardless of this is 5.18 or 5.19 material can you? : a) confirm that I've understood how the clearing vs cert-to-password works correctly ? b) confirm that despite you using a test BIOS the WMI API for this is final and that it will *not* change before there are production BIOS-es with this ? c) submit a version to clarify the clearing vs cert-to-password thing, e.g.: @@ -276,6 +276,8 @@ Description: 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. Regards, Hans > --- > Changes in v2: > - Combined set_signature with signature and moved save_signature under > the authorisation folder > - Fixed mistake in example for clearing certificate > > .../testing/sysfs-class-firmware-attributes | 43 +++++++++++++++++++ > 1 file changed, 43 insertions(+) > > diff --git a/Documentation/ABI/testing/sysfs-class-firmware-attributes b/Documentation/ABI/testing/sysfs-class-firmware-attributes > index 13e31c6a0e9c..7ad52cf70ac9 100644 > --- a/Documentation/ABI/testing/sysfs-class-firmware-attributes > +++ b/Documentation/ABI/testing/sysfs-class-firmware-attributes > @@ -246,6 +246,49 @@ Description: > that is being referenced (e.g hdd0, hdd1 etc) > This attribute defaults to device 0. > > + 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. > + 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 > > > What: /sys/class/firmware-attributes/*/attributes/pending_reboot
