On Wed 2018-04-04 00:39:05, David Howells wrote: > Linus Torvalds <[email protected]> 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
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