Re: [PATCH V31 07/25] kexec_file: Restrict at runtime if the kernel is locked down

[Dave Young]

On 06/24/19 at 02:06pm, Matthew Garrett wrote:
> On Sun, Jun 23, 2019 at 6:52 PM Dave Young <dyoung@xxxxxxxxxx> wrote:
> >
> > On 06/21/19 at 01:18pm, Matthew Garrett wrote:
> > > I don't think so - we want it to be possible to load images if they
> > > have a valid signature.
> >
> > I know it works like this way because of the previous patch.  But from
> > the patch log "When KEXEC_SIG is not enabled, kernel should not load
> > images", it is simple to check it early for !IS_ENABLED(CONFIG_KEXEC_SIG) &&
> > kernel_is_locked_down(reason, LOCKDOWN_INTEGRITY)  instead of depending
> > on the late code to verify signature.  In that way, easier to
> > understand the logic, no?
> 
> But that combination doesn't enforce signature validation? We can't
> depend on !IS_ENABLED(CONFIG_KEXEC_SIG_FORCE) because then it'll
> enforce signature validation even if lockdown is disabled.

Ok, got your point. still something could be improved though, in the switch
chunk, the errno, reason and IS_ENABLED(CONFIG_KEXEC_SIG_FORCE) etc is
not necessary for this -EPERM case.

/* add some comment to describe the behavior */
if (ret && security_is_locked_down(LOCKDOWN_KEXEC)) {
	ret = -EPERM;
	goto out;
}

Thanks
Dave