linux-kernel - Re: [PATCH v5 2/4] module: panic: Taint the kernel when selftest modules load

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Date:   Thu, 7 Jul 2022 17:40:52 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     David Gow <davidgow@...gle.com>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Sebastian Reichel <sre@...nel.org>,
        John Ogness <john.ogness@...utronix.de>,
        Joe Fradley <joefradley@...gle.com>,
        Daniel Latypov <dlatypov@...gle.com>,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Aaron Tomlin <atomlin@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v5 2/4] module: panic: Taint the kernel when selftest
 modules load

On Sat, Jul 02, 2022 at 12:09:57PM +0800, David Gow wrote:
> Taint the kernel with TAINT_TEST whenever a test module loads, by adding
> a new "TEST" module property, and setting it for all modules in the
> tools/testing directory. This property can also be set manually, for
> tests which live outside the tools/testing directory with:
> MODULE_INFO(test, "Y");
> 
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: David Gow <davidgow@...gle.com>
> ---
>  kernel/module/main.c  | 7 +++++++
>  scripts/mod/modpost.c | 3 +++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index fed58d30725d..730503561eb0 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1988,6 +1988,13 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
>  	/* Set up license info based on the info section */
>  	set_license(mod, get_modinfo(info, "license"));
>  
> +	if (!get_modinfo(info, "test")) {
> +		if (!test_taint(TAINT_TEST))
> +			pr_warn_once("%s: loading test module taints kernel.\n",
> +				     mod->name);
> +		add_taint_module(mod, TAINT_TEST, LOCKDEP_STILL_OK);
> +	}
> +
>  	return 0;
>  }
>  
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 29d5a841e215..5937212b4433 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -2191,6 +2191,9 @@ static void add_header(struct buffer *b, struct module *mod)
>  
>  	if (strstarts(mod->name, "drivers/staging"))
>  		buf_printf(b, "\nMODULE_INFO(staging, \"Y\");\n");
> +
> +	if (strstarts(mod->name, "tools/testing"))
> +		buf_printf(b, "\nMODULE_INFO(test, \"Y\");\n");
>  }
>  
>  static void add_exported_symbols(struct buffer *buf, struct module *mod)
> -- 
> 2.37.0.rc0.161.g10f37bed90-goog
> 
> 

Hi David,

This change has landed in linux-next as commit e20729ede7ed ("module:
panic: taint the kernel when selftest modules load") and on all of my
test machines, I see this new message printed, even though as far as I
am aware, I am not loading any testing modules. For example, in QEMU, I
see:

[    0.596978] serio: loading test module taints kernel.

and on my Honeycomb LX2, I see:

[    5.400861] fuse: loading test module taints kernel.

It seems like the get_modinfo() check might be wrong? The following diff
resolves it for me, I can send a formal patch if necessary (although it
appears to have gone in via -mm so I assume Andrew can squash this in).

Cheers,
Nathan

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 730503561eb0..4f91e41b8bc9 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1988,7 +1988,7 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
 	/* Set up license info based on the info section */
 	set_license(mod, get_modinfo(info, "license"));
 
-	if (!get_modinfo(info, "test")) {
+	if (get_modinfo(info, "test")) {
 		if (!test_taint(TAINT_TEST))
 			pr_warn_once("%s: loading test module taints kernel.\n",
 				     mod->name);