[Bug 1798863] Re: 18.10 kernel does not appear to validate kernel module signatures correctly

[Daniel Dadap]

Cool, glad you were able to track down the problems. Sorry if my report
that module signature verification was disabled and couldn't be re-
enabled was misleading. That's what I thought was happening; I didn't
think to imagine that the enforcement of the "valid signature required"
policy wasn't taking place at all.

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Title:
  18.10 kernel does not appear to validate kernel module signatures
  correctly

Status in linux package in Ubuntu:
  In Progress
Status in shim package in Ubuntu:
  Invalid
Status in linux source package in Cosmic:
  In Progress
Status in shim source package in Cosmic:
  Invalid

Bug description:
  On a system with Ubuntu 18.10, with secure boot enabled, and a key
  enrolled in the MOK database, I am observing the following peculiar
  behaviors:

  * Signature verification appears to be disabled, and cannot be enabled again. It appeared to be enabled previously, as loading of unsigned modules was failing, and `mokutil --enable-validation` runs without incident; however, upon the next boot when attempting to confirm the change, MokManager prints an error message "Unable to delete Secure Boot state" after completing the password challenge.
  * As a result of signature verification being disabled, modules signed with untrusted keys taint the kernel instead of failing to load outright.
  * Regardless of signature verification being enabled or not, it seems that the key enrolled in the MOK is not being used for validating kernel module signatures. Modules signed with the key still fail the signature verification test and taint the kernel, even though the key is visible in the output of `mokutil --list-enrolled`, and testing the key with `mokutil --test-key` shows that it's enrolled. Also, a message acknowledging the key appears in dmesg: Loaded UEFI:MokListRT cert 'nvidia-installer generated signing key: 90c957eb56dfb04d8734d54fb614ef5af6c69318' linked to secondary sys keyring
  * Also, somewhat strangely, in this state with module signature verification not being enforced, attempting to load a completely unsigned kernel module suceeds, and doesn't even log a kernel message about a missing/invalid signature, or taint the kernel.

  Apport report attached, which includes dmesg log showing the kernel
  acknowledging the key enrolled in the MOK database, and a signature
  verification failure and subsequent successful loading of a module
  signed with that key:

   [    4.234093] Loaded UEFI:MokListRT cert 'nvidia-installer generated signing key: 90c957eb56dfb04d8734d54fb614ef5af6c69318' linked to secondary sys keyring
  ...
   [    6.628452] nvidia: module verification failed: signature and/or required key missing - tainting kernel
  ...
   [    6.637252] nvidia-nvlink: Nvlink Core is being initialized, major device number 238
   [    6.637507] nvidia 0000:01:00.0: enabling device (0006 -> 0007)
   [    6.637620] nvidia 0000:01:00.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=none:owns=none
   [    6.737216] NVRM: loading NVIDIA UNIX x86_64 Kernel Module  410.66  Wed Oct 10 12:01:53 CDT 2018 (using threaded interrupts)

  This system dual-boots Ubuntu 18.04 and Ubuntu 18.10: when booted into Ubuntu 18.04, signatures made with the same key are recognized as valid. Hence, I suspect that something changed in the Ubuntu 18.10 kernel which is causing signature verification to function in an unexpected way.
  --- 
  ProblemType: Bug
  ApportVersion: 2.20.10-0ubuntu13
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  danix      1729 F.... pulseaudio
  DistroRelease: Ubuntu 18.10
  InstallationDate: Installed on 2018-10-23 (0 days ago)
  InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3)
  NonfreeKernelModules: nvidia_uvm nvidia
  Package: linux (not installed)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.18.0-10-generic root=/dev/mapper/ubuntu--vg-root ro quiet splash nouveau.modeset=0
  ProcVersionSignature: Ubuntu 4.18.0-10.11-generic 4.18.12
  RelatedPackageVersions:
   linux-restricted-modules-4.18.0-10-generic N/A
   linux-backports-modules-4.18.0-10-generic  N/A
   linux-firmware                             1.175
  Tags:  cosmic
  Uname: Linux 4.18.0-10-generic x86_64
  UnreportableReason: This report is about a package that is not installed.
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  _MarkForUpload: False
  dmi.bios.date: 03/20/2018
  dmi.bios.vendor: HP
  dmi.bios.version: P70 Ver. 01.18
  dmi.board.name: 8270
  dmi.board.vendor: HP
  dmi.board.version: KBC Version 46.67
  dmi.chassis.type: 10
  dmi.chassis.vendor: HP
  dmi.modalias: dmi:bvnHP:bvrP70Ver.01.18:bd03/20/2018:svnHP:pn:pvr:rvnHP:rn8270:rvrKBCVersion46.67:cvnHP:ct10:cvr:
  dmi.product.family: 103C_5336AN HP ZBook
  dmi.sys.vendor: HP

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