linux-kernel - Re: [PATCH 1/2] module: Restrict module namespace access to in-tree modules

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Message-ID: <d18973b8-3b52-4786-b5ab-94208495c8b0@amd.com>
Date: Tue, 8 Jul 2025 13:24:58 +0530
From: Shivank Garg <shivankg@....com>
To: Vlastimil Babka <vbabka@...e.cz>, Matthias Maennich
 <maennich@...gle.com>, Jonathan Corbet <corbet@....net>,
 Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez
 <da.gomez@...sung.com>, Masahiro Yamada <masahiroy@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>,
 Nicolas Schier <nicolas.schier@...ux.dev>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: Christoph Hellwig <hch@...radead.org>,
 Peter Zijlstra <peterz@...radead.org>, David Hildenbrand <david@...hat.com>,
 "Jiri Slaby (SUSE)" <jirislaby@...nel.org>,
 Stephen Rothwell <sfr@...b.auug.org.au>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
 linux-kbuild@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] module: Restrict module namespace access to in-tree
 modules



On 7/8/2025 12:58 PM, Vlastimil Babka wrote:
> The module namespace support has been introduced to allow restricting
> exports to specific modules only, and intended for in-tree modules such
> as kvm. Make this intention explicit by disallowing out of tree modules
> both for the module loader and modpost.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  Documentation/core-api/symbol-namespaces.rst | 5 +++--
>  kernel/module/main.c                         | 3 ++-
>  scripts/mod/modpost.c                        | 6 +++++-
>  3 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/core-api/symbol-namespaces.rst b/Documentation/core-api/symbol-namespaces.rst
> index 32fc73dc5529e8844c2ce2580987155bcd13cd09..dc228ac738a5cdc49cc736c29170ca96df6a28dc 100644
> --- a/Documentation/core-api/symbol-namespaces.rst
> +++ b/Documentation/core-api/symbol-namespaces.rst
> @@ -83,13 +83,14 @@ Symbols exported using this macro are put into a module namespace. This
>  namespace cannot be imported.
>  
>  The macro takes a comma separated list of module names, allowing only those
> -modules to access this symbol. Simple tail-globs are supported.
> +modules to access this symbol. The access is restricted to in-tree modules.
> +Simple tail-globs are supported.
>  
>  For example::
>  
>    EXPORT_SYMBOL_GPL_FOR_MODULES(preempt_notifier_inc, "kvm,kvm-*")
>  
> -will limit usage of this symbol to modules whoes name matches the given
> +will limit usage of this symbol to in-tree modules whoes name matches the given
>  patterns.
>  
>  How to use Symbols exported in Namespaces
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 413ac6ea37021bc8ae260f624ca2745ed85333fc..ec7d8daa0347e3b65713396d6b6d14c2cb0270d3 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1157,7 +1157,8 @@ static int verify_namespace_is_imported(const struct load_info *info,
>  	namespace = kernel_symbol_namespace(sym);
>  	if (namespace && namespace[0]) {
>  
> -		if (verify_module_namespace(namespace, mod->name))
> +		if (get_modinfo(info, "intree") &&
> +		    verify_module_namespace(namespace, mod->name))
>  			return 0;
>  
>  		for_each_modinfo_entry(imported_namespace, info, "import_ns") {
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 5ca7c268294ebb65acb0ba52a671eddca9279c61..d78be9834ed75f4b6ddb9af02a300a9bcc9234cc 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1695,7 +1695,8 @@ void buf_write(struct buffer *buf, const char *s, int len)
>   * @modname: module name
>   *
>   * If @namespace is prefixed with "module:" to indicate it is a module namespace
> - * then test if @modname matches any of the comma separated patterns.
> + * then test if @modname matches any of the comma separated patterns. Access to
> + * module namespaces is restricted to in-tree modules only.
>   *
>   * The patterns only support tail-glob.
>   */
> @@ -1706,6 +1707,9 @@ static bool verify_module_namespace(const char *namespace, const char *modname)
>  	const char *sep;
>  	bool glob;
>  
> +	if (external_module)
> +		return false;
> +
>  	if (!strstarts(namespace, prefix))
>  		return false;
>  
> 

Reviewed-by: Shivank Garg <shivankg@....com>

Thanks,
Shivank