Re: [PATCH] module: Harden STRICT_MODULE_RWX

Miroslav Benes
2020-04-06T09:55:42Z

On Fri, 3 Apr 2020, Josh Poimboeuf wrote:

> On Fri, Apr 03, 2020 at 06:37:16PM +0200, Peter Zijlstra wrote:
> > +{
> > + int i;
> > +
> > + for (i = 0; i < hdr->e_shnum; i++) {
> > + if (sechdrs[i].sh_flags & (SHF_EXECINSTR|SHF_WRITE))
> > + return -ENOEXEC;
>
> I think you only want the error when both are set?
>
> if (sechdrs[i].sh_flags & (SHF_EXECINSTR|SHF_WRITE) == (SHF_EXECINSTR|SHF_WRITE))

A section with SHF_EXECINSTR and SHF_WRITE but without SHF_ALLOC would be
strange though, no? It wouldn't be copied to the final module later
anyway.

Looking at layout_sections()... a section with
SHF_EXECINSTR|SHF_WRITE|SHF_ALLOC would not be counted at all. However,
move_module() later copies everything with SHF_ALLOC flag to the final
module. If there is WXA section, there would be a bug because the
allocation there would not get the correct size. In that case it is
important to error out early as you're proposing.

Am I missing something?

Miroslav