MacOS High Sierra KEXT Loading - Are there any ways to cancel user approval?

To echo what people are saying in the comments, I found that the accepted solution did not work. I also had to reset the PRAM.

Working steps:

1. Create the following script somewhere on your filesystem (you will be running this from recovery mode, so you won't be able to copy and paste in that mode). You will need to replace TEAMID1234 with the team ID of the kext(s) you want to revoke consent for. Note that the full paths to /Volumes/Macintosh\ HD are required in recovery mode.

   I called my script /Users/me/revoke_kext_consent.sh, and ran chmod +x /Users/me/revoke_kext_consent.sh.

#!/bin/sh -e
/Volumes/Macintosh\ HD/usr/bin/sqlite3 /Volumes/Macintosh\ HD/var/db/SystemPolicyConfiguration/KextPolicy 'delete from kext_policy where team_id="TEAMID1234";'
/Volumes/Macintosh\ HD/usr/bin/sqlite3 /Volumes/Macintosh\ HD/var/db/SystemPolicyConfiguration/KextPolicy 'delete from kext_load_history_v3 where team_id="TEAMID1234";'

2. Reboot into recovery mode (boot with Cmd-R)

3. Open Terminal, and run the above script (/Volumes/Macintosh\ HD/Users/me/revoke_kext_consent.sh).

4. Reboot and reset the PRAM (boot with Cmd-Opt-P-R)

The information about approvals is stored in sqlite3 database:

/var/db/SystemPolicyConfiguration/KextPolicy

The tables you're interested in are: kext_policy and kext_load_history_v3. E.g. here is how you can view the data and the table schema:

sqlite3 /var/db/SystemPolicyConfiguration/KextPolicy

sqlite> select * from kext_policy;
54GTJ2AU36|com.joshuawise.kexts.HoRNDIS|1|Joshua Wise|1

sqlite> .schema kext_policy
CREATE TABLE kext_policy ( team_id TEXT, bundle_id TEXT, allowed BOOLEAN, developer_name TEXT, flags INTEGER, PRIMARY KEY (team_id, bundle_id) );

Removing the approval is tricker, since the System Integrity Protection does not allow you to modify the database. So, you'd need to reboot into a recovery partition, or a different MacOS installation, then cd into the root of your volume, and run the commands like these (replace with your team_id, or use other criteria):

usr/bin/sqlite3 var/db/SystemPolicyConfiguration/KextPolicy
delete from kext_load_history_v3 where team_id='54GTJ2AU36';
delete from kext_policy where team_id='54GTJ2AU36';
.quit