Re: [PATCH v5] RO/NX protection for loadable kernel modules

[Rusty Russell <rusty@rustcorp.com.au>]

On Sun, 12 Jul 2009 01:19:58 am Arjan van de Ven wrote:
> Rusty Russell <rusty@rustcorp.com.au> wrote:
> > I have a question about this patch though: I think it's unsafe in
> > general to mark the last partial page as NX (we asked for executable
> > pages, this could remove executable from some unrelated allocation).
>
> we vmalloc / g_f_p modules right? so we don't share the last page.

Historically yes, but I don't think we should be counting on it.  It makes 
sense to kmalloc for small modules, and it's arch specific code.

OTOH, a quick grep shows currently only cris does kmalloc, and that's a config 
option.

It might be time to unify this code.  If we rename MODULE_START to 
MODULE_VADDR on MIPS, then ignoring CRIS there's only two real variants; 
vmalloc and __vmalloc.

(I like the idea of trying kmalloc and falling back, simply because it reduces 
TLB pressure, but that's probably best done after unification).

Thoughts?
Rusty.