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

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Message-ID: <20200403165631.hrxxm3pnzqa4vxln@treble>
Date:   Fri, 3 Apr 2020 11:56:31 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     jeyu@...nel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>, keescook@...omium.org,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH] module: Harden STRICT_MODULE_RWX

On Fri, Apr 03, 2020 at 06:37:16PM +0200, Peter Zijlstra wrote:
> 
> We're very close to enforcing W^X memory, refuse to load modules that
> violate this principle per construction.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Jessica Yu <jeyu@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>  kernel/module.c |   24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2044,9 +2044,28 @@ static void module_enable_x(const struct
>  	frob_text(&mod->core_layout, set_memory_x);
>  	frob_text(&mod->init_layout, set_memory_x);
>  }
> +
> +static int module_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
> +			       char *secstrings, struct module *mod)

A verb would be nice: "module_enforce_rwx_sections"?

Shouldn't this be under STRICT_MODULE_RWX instead of
ARCH_HAS_STRICT_MODULE_RWX?

> +{
> +	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))

-- 
Josh