linux-kernel - Re: [PATCH 04/10] module loader: use kflagstab instead of *

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Message-ID: <fdec30b6-e3d0-4694-ba29-3bc99960346a@suse.com>
Date: Wed, 8 Oct 2025 15:19:05 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: Siddharth Nayyar <sidnayyar@...gle.com>
Cc: Nathan Chancellor <nathan@...nel.org>,
 Luis Chamberlain <mcgrof@...nel.org>, Sami Tolvanen
 <samitolvanen@...gle.com>, Nicolas Schier <nicolas.schier@...ux.dev>,
 Arnd Bergmann <arnd@...db.de>, linux-kbuild@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-modules@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/10] module loader: use kflagstab instead of *_gpl
 sections

On 8/29/25 12:54 PM, Siddharth Nayyar wrote:
> Read __kflagstab section for vmlinux and modules to determine whether
> kernel symbols are GPL only.
> 
> Signed-off-by: Siddharth Nayyar <sidnayyar@...gle.com>
> ---
> [...]
> @@ -2607,6 +2605,7 @@ static int find_module_sections(struct module *mod, struct load_info *info)
>  				     sizeof(*mod->gpl_syms),
>  				     &mod->num_gpl_syms);
>  	mod->gpl_crcs = section_addr(info, "__kcrctab_gpl");
> +	mod->flagstab = section_addr(info, "__kflagstab");
>  
>  #ifdef CONFIG_CONSTRUCTORS
>  	mod->ctors = section_objs(info, ".ctors",

The module loader should always at least get through the signature and
blacklist checks without crashing due to a corrupted ELF file. After
that point, the module content is to be trusted, but we try to error out
for most issues that would cause problems later on.

For __kflagstab, I believe it would be useful to check that the section
is present to prevent the code from potentially crashing due to a NULL
dereference deep in find_exported_symbol_in_section(). You can rename
check_export_symbol_versions() to check_export_symbol_sections() and add
the following:

	if (mod->num_syms && !mod->flagstab) {
		pr_err("%s: no flags for exported symbols\n", mod->name);
		return -ENOEXEC;
	}

-- 
Thanks,
Petr