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    SubjectRe: [GIT PULL] Kernel lockdown for secure boot
    On Wed 2018-04-04 00:39:05, David Howells wrote:
    > Linus Torvalds <torvalds@linux-foundation.org> 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.
    >
    > (2) If the kernel isn't booted in secure boot mode, then there's the
    > opportunity to tamper before the kernel even starts booting.
    >
    > (3) There doesn't seem any point in booting in secure boot mode if you don't
    > protect the running kernel image against tampering. What does it mean to
    > be in "secure boot mode" in that case? If the kernel can be tampered
    > with, it would seem to be, by definition, insecure.

    This one is not true, either.

    If kernel does "printk(KERN_CRIT "loading unsigned module");
    mdelay(10000);", it is useful for secure boot and provides way to
    owner to play.

    Nokia N9 / N950 uses this kind of "security" for example. It is rather
    annoying but better than not being able to run custom kernels at all.
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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