Re: [GIT PULL] Kernel lockdown for secure boot

[Andy Lutomirski]

On Tue, Apr 3, 2018 at 4:39 PM, David Howells <dhowells@xxxxxxxxxx> wrote:
> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
>> The same thing is true of some lockdown patch. Maybe it's a good thing
>> in general. But whether it's a good thing is _entirely_ independent of
>> any secure boot issue. I can see using secure boot without it, but I
>> can very much also see using lockdown without secure boot.
>>
>> The two things are simply entirely orthogonal. They have _zero_
>> overlap. I'm not seeing why they'd be linked at all in any way.
>
> I'm not sure I agree.  Here's my reasoning:
>
>  (1) Lockdown mode really needs to activated during kernel boot, before
>      userspace has a chance to run, otherwise there's a window of opportunity
>      in which the kernel *isn't* locked down.

That's simply not true.  A sensible verified boot chain (a la Chrome
OS) is likely to load, as one verified chunk, a kernel and initramfs.
Then initramfs can flip on lockdown all by itself before it enables
networking or any other attack vectors.