Messages in this thread | | | From | Matthew Garrett <> | Date | Wed, 04 Apr 2018 16:26:43 +0000 | Subject | Re: [GIT PULL] Kernel lockdown for secure boot |
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On Tue, Apr 3, 2018 at 11:56 PM Peter Dolding <oiaohm@gmail.com> wrote: > On Wed, Apr 4, 2018 at 11:13 AM, Matthew Garrett <mjg59@google.com> wrote:
> > There are four cases: > > > > Verified Boot off, lockdown off: Status quo in distro and mainline kernels > > Verified Boot off, lockdown on: Perception of security improvement that's > > trivially circumvented (and so bad) > > Verified Boot on, lockdown off: Perception of security improvement that's > > trivially circumvented (and so bad), status quo in mainline kernels > > Verified Boot on, lockdown on: Security improvement, status quo in distro > > kernels > > > > Of these four options, only two make sense. The most common implementation > > of Verified Boot on x86 platforms is UEFI Secure Boot,
> Stop right there. Verified boot does not have to be UEFI secureboot. > You could be using a uboot verified boot or > https://www.coreboot.org/git-docs/Intel/vboot.html google vboot. > Neither of these provide flags to kernel to say they have been > performed.
They can be modified to set the appropriate bit in the bootparams - the reason we can't do that in the UEFI case is that Linux can be built as a UEFI binary that the firmware execute directly, and so the firmware has no way to set that flag.
> Now Verified Boot on, lockdown off. Insanely this can be required in > diagnostic on some embedded platform because EFI secureboot does not > have a off switch. These are platforms where they don't boot if > they don't have a PK and KEK set installed. Yes some of these is jtag > the PK and KEK set in.
> The fact that this Verified Boot on, lockdown off causes trouble > points to a clear problem. User owns the hardware they should have > the right to defeat secureboot if they wish to.
Which is why Shim allows you to disable validation if you prove physical user presence.
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