On Thu, Oct 1, 2015 at 2:12 AM, Ingo Molnar <mi...@kernel.org> wrote: > > * Thomas Gleixner <t...@linutronix.de> wrote: > >> On Mon, 28 Sep 2015, Kees Cook wrote: >> > > --- a/arch/x86/mm/init_64.c >> > > +++ b/arch/x86/mm/init_64.c >> > > @@ -1132,7 +1132,7 @@ void mark_rodata_ro(void) >> > > * has been zapped already via cleanup_highmem(). >> > > */ >> > > all_end = roundup((unsigned long)_brk_end, PMD_SIZE); >> > > - set_memory_nx(rodata_start, (all_end - rodata_start) >> >> > > PAGE_SHIFT); >> > > + set_memory_nx(text_end, (all_end - text_end) >> PAGE_SHIFT); >> > > >> > > rodata_test(); >> > > >> > > >> > >> > That should work, yeah. I'd still like to find the default permissions and >> > make them W+nx, though. Regardless, let's get the above added. >> >> The default permissions are set at boot time when setting up the early page >> tables. When we split them up later on we inherit the PTE bits and then we do >> that _ro/nx cleanup after the overall layout has been settled. >> >> We can't make them W+nx in the early setup without shooting ourself in the >> foot, >> because we only set up at the pud/pmd level. > > So I think at minimum we should do a (debug) scan in late init, of the whole > range, for any leftover WX permissions? That would have caught this bug. (and > might catch other existing bugs that might occur with various > configs/hw-layouts.)
I think this would be great. I'd like to disassociate it from PTDUMP, though, since that exposes kernel address to userspace. It'd be nice to have the check without also the debugfs entry. -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
