Re: [PATCH] module: Harden STRICT_MODULE_RWX

[Miroslav Benes]

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