Re: [PATCH v3] module: extend 'rodata=off' boot cmdline parameter to module mappings

Re: [PATCH v3] module: extend 'rodata=off' boot cmdline parameter to module mappings

[Andreas Ziegler]

Hi Akashi,

your patch "module: extend 'rodata=off' boot cmdline parameter to module
mappings" showed up in linux-next today, and I noticed a small error in it.

The first modified #ifdef is fine, the second one, however, has a spelling
mistake in it: the CONFIG_ variable should be CONFIG_DEBUG_SET_MODULE_RONX
instead of CONFIG_SET_MODULE_RONX (note the missing DEBUG).

I noticed it by running 'scripts/checkkconfigsymbols -f --force -f
next-20161124..next-20161128', which is essentialy diffing the last two
linux-next releases and looks for undefined/unknown Kconfig symbols.
You can also run the script on single commits with -c to test them.

Best regards,

Andreas

Re: [PATCH v3] module: extend 'rodata=off' boot cmdline parameter to module mappings

[AKASHI Takahiro]

On Mon, Nov 28, 2016 at 08:59:40AM +0100, Andreas Ziegler wrote:
> Hi Akashi,
> 
> your patch "module: extend 'rodata=off' boot cmdline parameter to module
> mappings" showed up in linux-next today, and I noticed a small error in it.
> 
> The first modified #ifdef is fine, the second one, however, has a spelling
> mistake in it: the CONFIG_ variable should be CONFIG_DEBUG_SET_MODULE_RONX
> instead of CONFIG_SET_MODULE_RONX (note the missing DEBUG).

Thank you for pointing this out.
(I didn't notice it because DEBUG_RODATA is always on on arm64.)

Rusty, Jessica, should I submit v4 to correct it?

-Takahiro AKASHI

> I noticed it by running 'scripts/checkkconfigsymbols -f --force -f
> next-20161124..next-20161128', which is essentialy diffing the last two
> linux-next releases and looks for undefined/unknown Kconfig symbols.
> You can also run the script on single commits with -c to test them.
> 
> Best regards,
> 
> Andreas

[kernel-hardening] Re: [PATCH v3] module: extend 'rodata=off' boot cmdline parameter to module mappings

[AKASHI Takahiro]

On Mon, Nov 28, 2016 at 08:59:40AM +0100, Andreas Ziegler wrote:
> Hi Akashi,
> 
> your patch "module: extend 'rodata=off' boot cmdline parameter to module
> mappings" showed up in linux-next today, and I noticed a small error in it.
> 
> The first modified #ifdef is fine, the second one, however, has a spelling
> mistake in it: the CONFIG_ variable should be CONFIG_DEBUG_SET_MODULE_RONX
> instead of CONFIG_SET_MODULE_RONX (note the missing DEBUG).

Thank you for pointing this out.
(I didn't notice it because DEBUG_RODATA is always on on arm64.)

Rusty, Jessica, should I submit v4 to correct it?

-Takahiro AKASHI

> I noticed it by running 'scripts/checkkconfigsymbols -f --force -f
> next-20161124..next-20161128', which is essentialy diffing the last two
> linux-next releases and looks for undefined/unknown Kconfig symbols.
> You can also run the script on single commits with -c to test them.
> 
> Best regards,
> 
> Andreas

Re: module: extend 'rodata=off' boot cmdline parameter to module mappings

[Jessica Yu]

+++ AKASHI Takahiro [28/11/16 18:18 +0900]:
>On Mon, Nov 28, 2016 at 08:59:40AM +0100, Andreas Ziegler wrote:
>> Hi Akashi,
>>
>> your patch "module: extend 'rodata=off' boot cmdline parameter to module
>> mappings" showed up in linux-next today, and I noticed a small error in it.
>>
>> The first modified #ifdef is fine, the second one, however, has a spelling
>> mistake in it: the CONFIG_ variable should be CONFIG_DEBUG_SET_MODULE_RONX
>> instead of CONFIG_SET_MODULE_RONX (note the missing DEBUG).
>
>Thank you for pointing this out.
>(I didn't notice it because DEBUG_RODATA is always on on arm64.)
>
>Rusty, Jessica, should I submit v4 to correct it?

Andreas, Akashi -

The typo has been fixed with Arnd's patch:

   http://lkml.kernel.org/r/20161128145931.3350661-1-arnd@arndb.de

Thanks for finding the issue!

Jessica

[kernel-hardening] Re: module: extend 'rodata=off' boot cmdline parameter to module mappings

[Jessica Yu]

+++ AKASHI Takahiro [28/11/16 18:18 +0900]:
>On Mon, Nov 28, 2016 at 08:59:40AM +0100, Andreas Ziegler wrote:
>> Hi Akashi,
>>
>> your patch "module: extend 'rodata=off' boot cmdline parameter to module
>> mappings" showed up in linux-next today, and I noticed a small error in it.
>>
>> The first modified #ifdef is fine, the second one, however, has a spelling
>> mistake in it: the CONFIG_ variable should be CONFIG_DEBUG_SET_MODULE_RONX
>> instead of CONFIG_SET_MODULE_RONX (note the missing DEBUG).
>
>Thank you for pointing this out.
>(I didn't notice it because DEBUG_RODATA is always on on arm64.)
>
>Rusty, Jessica, should I submit v4 to correct it?

Andreas, Akashi -

The typo has been fixed with Arnd's patch:

   http://lkml.kernel.org/r/20161128145931.3350661-1-arnd@arndb.de

Thanks for finding the issue!

Jessica

[PATCH v3] module: extend 'rodata=off' boot cmdline parameter to module mappings

[AKASHI Takahiro]

The current "rodata=off" parameter disables read-only kernel mappings
under CONFIG_DEBUG_RODATA:
    commit d2aa1acad22f ("mm/init: Add 'rodata=off' boot cmdline parameter
    to disable read-only kernel mappings")

This patch is a logical extension to module mappings ie. read-only mappings
at module loading can be disabled even if CONFIG_DEBUG_SET_MODULE_RONX
(mainly for debug use). Please note, however, that it only affects RO/RW
permissions, keeping NX set.

This is the first step to make CONFIG_DEBUG_SET_MODULE_RONX mandatory
(always-on) in the future as CONFIG_DEBUG_RODATA on x86 and arm64.

Suggested-by: and Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jessica Yu <jeyu@redhat.com>
---
v3:
  * merge if-statements in disable_ro_nx()
v2:
  * use CONFIG_DEBUG_RODATA/SET_MODULE_RONX guards better where appropriate
  * make "rodata_enabled" variable as __ro_after_init
v1:
  * remove RFC's "module_ronx=" and merge it with "rodata="
  * always keep NX set if CONFIG_SET_MODULE_RONX

 include/linux/init.h |  3 +++
 init/main.c          |  7 +++++--
 kernel/module.c      | 20 +++++++++++++++++---
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index e30104c..885c3e6 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -126,6 +126,9 @@ void prepare_namespace(void);
 void __init load_default_modules(void);
 int __init init_rootfs(void);
 
+#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_DEBUG_SET_MODULE_RONX)
+extern bool rodata_enabled;
+#endif
 #ifdef CONFIG_DEBUG_RODATA
 void mark_rodata_ro(void);
 #endif
diff --git a/init/main.c b/init/main.c
index 2858be7..959a242 100644
--- a/init/main.c
+++ b/init/main.c
@@ -81,6 +81,7 @@
 #include <linux/integrity.h>
 #include <linux/proc_ns.h>
 #include <linux/io.h>
+#include <linux/cache.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -914,14 +915,16 @@ static int try_to_run_init_process(const char *init_filename)
 
 static noinline void __init kernel_init_freeable(void);
 
-#ifdef CONFIG_DEBUG_RODATA
-static bool rodata_enabled = true;
+#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_SET_MODULE_RONX)
+bool rodata_enabled __ro_after_init = true;
 static int __init set_debug_rodata(char *str)
 {
 	return strtobool(str, &rodata_enabled);
 }
 __setup("rodata=", set_debug_rodata);
+#endif
 
+#ifdef CONFIG_DEBUG_RODATA
 static void mark_readonly(void)
 {
 	if (rodata_enabled)
diff --git a/kernel/module.c b/kernel/module.c
index f57dd63..6ad4b3f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1910,6 +1910,9 @@ static void frob_writable_data(const struct module_layout *layout,
 /* livepatching wants to disable read-only so it can frob module. */
 void module_disable_ro(const struct module *mod)
 {
+	if (!rodata_enabled)
+		return;
+
 	frob_text(&mod->core_layout, set_memory_rw);
 	frob_rodata(&mod->core_layout, set_memory_rw);
 	frob_ro_after_init(&mod->core_layout, set_memory_rw);
@@ -1919,6 +1922,9 @@ void module_disable_ro(const struct module *mod)
 
 void module_enable_ro(const struct module *mod, bool after_init)
 {
+	if (!rodata_enabled)
+		return;
+
 	frob_text(&mod->core_layout, set_memory_ro);
 	frob_rodata(&mod->core_layout, set_memory_ro);
 	frob_text(&mod->init_layout, set_memory_ro);
@@ -1951,6 +1957,9 @@ void set_all_modules_text_rw(void)
 {
 	struct module *mod;
 
+	if (!rodata_enabled)
+		return;
+
 	mutex_lock(&module_mutex);
 	list_for_each_entry_rcu(mod, &modules, list) {
 		if (mod->state == MODULE_STATE_UNFORMED)
@@ -1967,6 +1976,9 @@ void set_all_modules_text_ro(void)
 {
 	struct module *mod;
 
+	if (!rodata_enabled)
+		return;
+
 	mutex_lock(&module_mutex);
 	list_for_each_entry_rcu(mod, &modules, list) {
 		if (mod->state == MODULE_STATE_UNFORMED)
@@ -1980,10 +1992,12 @@ void set_all_modules_text_ro(void)
 
 static void disable_ro_nx(const struct module_layout *layout)
 {
-	frob_text(layout, set_memory_rw);
-	frob_rodata(layout, set_memory_rw);
+	if (rodata_enabled) {
+		frob_text(layout, set_memory_rw);
+		frob_rodata(layout, set_memory_rw);
+		frob_ro_after_init(layout, set_memory_rw);
+	}
 	frob_rodata(layout, set_memory_x);
-	frob_ro_after_init(layout, set_memory_rw);
 	frob_ro_after_init(layout, set_memory_x);
 	frob_writable_data(layout, set_memory_x);
 }
-- 
2.10.0