linux-kernel - Re: [PATCH] module: Harden STRICT_MODULE

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Date:   Mon, 6 Apr 2020 11:55:39 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     Peter Zijlstra <peterz@...radead.org>, jeyu@...nel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        keescook@...omium.org
Subject: Re: [PATCH] module: Harden STRICT_MODULE_RWX

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