[kernel-hardening] [PATCH] add the option of fortified string.h functions

[Michael Ellerman]

Daniel Axtens <dja at axtens.net> writes:

> Hi Daniel and ppc people,
>
> (ppc people: this does some compile and run time bounds checking on
> string functions. It's cool - currently it picks up a lot of random
> things so it will require some more work across the tree, but hopefully
> it will eventually hit mainline.)

Cool! 

> Once those were added, I needed to disable fortification in prom_init.c,
> as we apparently can't have new symbols there. (I don't understand that
> file so I haven't dug into it.)

We can refer to new symbols from there, we just have a script to check
we don't refer to anything new inadvertently.

prom_init() is sort of a shim that runs before the kernel, except it's
linked with the kernel, but ideally wouldn't be, but we never bothered
actually making it separate. O_o

> We also have problems with the feature fixup tests leading to a panic on
> boot. It relates to getting what I think are asm labels(?) and how we
> address them. I have just disabled fortify here for now; I think the
> code could be rewritten to take the labels as unsigned char *, but I
> haven't dug into it.

OK, yeah it's using asm labels to compare the patched code vs the
expected result. Can probably be fixed by making them char[] like we do
for other things like __start_interrupts etc.

cheers