[Bug 1604873] [NEW] MokSBStateRT strictly inferior to /proc/sys/kernel/moksbstate_disabled

[Steve Langasek]

Public bug reported:

update-secureboot-policy tries to check whether MOK's override has disabled SecureBoot state.  However, since the real variable in nvram is not accessible after boot, it needs to use a proxy for this information.  There are two that it tries to use:
 - We've specified how shim can mirror the MokSBState variable to MokSBStateRT at boot time, to expose this information to the OS (but this is not implemented in current shim).
 - The recent kernels which honor MokSBState also include support for exposing this value as  /proc/sys/kernel/moksbstate_disabled.

Neither of these is guaranteed to be present on any given system.
However, if present, the kernel variable should be *unconditionally*
preferred over the efi "shadow" variable - because the kernel variable
is immutable, whereas MokSBStateRT is just another nvram variable that
things can overwrite (though they shouldn't).

We have heard at least one report internally of a system where something
other than our shim is setting the value of MokSBStateRT and confusing
update-secureboot-policy, so this will be a priority to also fix in SRU.

** Affects: shim-signed (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: shim-signed (Ubuntu Precise)
     Importance: Undecided
         Status: New

** Affects: shim-signed (Ubuntu Trusty)
     Importance: Undecided
         Status: New

** Affects: shim-signed (Ubuntu Wily)
     Importance: Undecided
         Status: New

** Affects: shim-signed (Ubuntu Xenial)
     Importance: Undecided
         Status: New

** Also affects: shim-signed (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Also affects: shim-signed (Ubuntu Precise)
   Importance: Undecided
       Status: New

** Also affects: shim-signed (Ubuntu Trusty)
   Importance: Undecided
       Status: New

** Also affects: shim-signed (Ubuntu Wily)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1604873

Title:
  MokSBStateRT strictly inferior to /proc/sys/kernel/moksbstate_disabled

Status in shim-signed package in Ubuntu:
  New
Status in shim-signed source package in Precise:
  New
Status in shim-signed source package in Trusty:
  New
Status in shim-signed source package in Wily:
  New
Status in shim-signed source package in Xenial:
  New

Bug description:
  update-secureboot-policy tries to check whether MOK's override has disabled SecureBoot state.  However, since the real variable in nvram is not accessible after boot, it needs to use a proxy for this information.  There are two that it tries to use:
   - We've specified how shim can mirror the MokSBState variable to MokSBStateRT at boot time, to expose this information to the OS (but this is not implemented in current shim).
   - The recent kernels which honor MokSBState also include support for exposing this value as  /proc/sys/kernel/moksbstate_disabled.

  Neither of these is guaranteed to be present on any given system.
  However, if present, the kernel variable should be *unconditionally*
  preferred over the efi "shadow" variable - because the kernel variable
  is immutable, whereas MokSBStateRT is just another nvram variable that
  things can overwrite (though they shouldn't).

  We have heard at least one report internally of a system where
  something other than our shim is setting the value of MokSBStateRT and
  confusing update-secureboot-policy, so this will be a priority to also
  fix in SRU.

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