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

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>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Link: http://lkml.kernel.org/r/20161114061505.15238-1-takahiro.akashi@linaro.org
Signed-off-by: Jessica Yu <jeyu@redhat.com>

1 files changed, 17 insertions, 3 deletions

diff --git a/kernel/module.c b/kernel/module.c
index 6281c70683d3..039ce82803f7 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1902,6 +1902,9 @@ 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);
@@ -1911,6 +1914,9 @@ 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);
@@ -1943,6 +1949,9 @@ 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)
@@ -1959,6 +1968,9 @@ 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) {
                 /*
@@ -1978,10 +1990,12 @@ 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);
 }