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

Message ID 20161020062458.14014-1-takahiro.akashi@linaro.org
State New
Headers show

Commit Message

AKASHI Takahiro Oct. 20, 2016, 6:24 a.m. UTC
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: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
---
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          |  2 +-
 kernel/module.c      | 21 ++++++++++++++++++---
 3 files changed, 21 insertions(+), 5 deletions(-)

Comments

Kees Cook Oct. 20, 2016, 8:48 p.m. UTC | #1
On Wed, Oct 19, 2016 at 11:24 PM, AKASHI Takahiro
<takahiro.akashi@linaro.org> wrote:
> 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: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> ---
> 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          |  2 +-
>  kernel/module.c      | 21 ++++++++++++++++++---
>  3 files changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/init.h b/include/linux/init.h
> index e30104c..20aa2eb 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -126,7 +126,8 @@ void prepare_namespace(void);
>  void __init load_default_modules(void);
>  int __init init_rootfs(void);
>
> -#ifdef CONFIG_DEBUG_RODATA
> +#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_DEBUG_SET_MODULE_RONX)
> +extern bool rodata_enabled;
>  void mark_rodata_ro(void);
>  #endif
>
> diff --git a/init/main.c b/init/main.c
> index 2858be7..92db2f3 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -915,7 +915,7 @@ 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;
> +bool rodata_enabled = true;

Is there a mismatch here between the extern ifdef and the bool ifdef?
I.e. shouldn't the ifdef here be || DEBUG_SET_MODULE_RONX too?

Also, can you mark this as __ro_after_init, since nothing changes it
after the kernel command line is parsed?

Otherwise, this looks fine to me.

-Kees
AKASHI Takahiro Oct. 21, 2016, 1:12 a.m. UTC | #2
On Thu, Oct 20, 2016 at 01:48:15PM -0700, Kees Cook wrote:
> On Wed, Oct 19, 2016 at 11:24 PM, AKASHI Takahiro
> <takahiro.akashi@linaro.org> wrote:
> > 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: Mark Rutland <mark.rutland@arm.com>
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > Cc: Rusty Russell <rusty@rustcorp.com.au>
> > ---
> > 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          |  2 +-
> >  kernel/module.c      | 21 ++++++++++++++++++---
> >  3 files changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/init.h b/include/linux/init.h
> > index e30104c..20aa2eb 100644
> > --- a/include/linux/init.h
> > +++ b/include/linux/init.h
> > @@ -126,7 +126,8 @@ void prepare_namespace(void);
> >  void __init load_default_modules(void);
> >  int __init init_rootfs(void);
> >
> > -#ifdef CONFIG_DEBUG_RODATA
> > +#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_DEBUG_SET_MODULE_RONX)
> > +extern bool rodata_enabled;
> >  void mark_rodata_ro(void);
> >  #endif
> >
> > diff --git a/init/main.c b/init/main.c
> > index 2858be7..92db2f3 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -915,7 +915,7 @@ 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;
> > +bool rodata_enabled = true;
> 
> Is there a mismatch here between the extern ifdef and the bool ifdef?
> I.e. shouldn't the ifdef here be || DEBUG_SET_MODULE_RONX too?

Yes.

> Also, can you mark this as __ro_after_init, since nothing changes it
> after the kernel command line is parsed?

Yes, yes.

Thanks,
-Takahiro AKASHI

> Otherwise, this looks fine to me.
> 
> -Kees
> 
> 
> -- 
> Kees Cook
> Nexus Security
Rusty Russell Oct. 26, 2016, 12:13 a.m. UTC | #3
AKASHI Takahiro <takahiro.akashi@linaro.org> writes:
> On Thu, Oct 20, 2016 at 01:48:15PM -0700, Kees Cook wrote:
>> On Wed, Oct 19, 2016 at 11:24 PM, AKASHI Takahiro
>> <takahiro.akashi@linaro.org> wrote:
>> > 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 patch looks good (except the minor issues noted by Kees); please CC
the followup version to Jessica as new module maintainer.

Thanks!
Rusty.

>> >
>> > 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: Mark Rutland <mark.rutland@arm.com>
>> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>> > Cc: Rusty Russell <rusty@rustcorp.com.au>
>> > ---
>> > 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          |  2 +-
>> >  kernel/module.c      | 21 ++++++++++++++++++---
>> >  3 files changed, 21 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/include/linux/init.h b/include/linux/init.h
>> > index e30104c..20aa2eb 100644
>> > --- a/include/linux/init.h
>> > +++ b/include/linux/init.h
>> > @@ -126,7 +126,8 @@ void prepare_namespace(void);
>> >  void __init load_default_modules(void);
>> >  int __init init_rootfs(void);
>> >
>> > -#ifdef CONFIG_DEBUG_RODATA
>> > +#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_DEBUG_SET_MODULE_RONX)
>> > +extern bool rodata_enabled;
>> >  void mark_rodata_ro(void);
>> >  #endif
>> >
>> > diff --git a/init/main.c b/init/main.c
>> > index 2858be7..92db2f3 100644
>> > --- a/init/main.c
>> > +++ b/init/main.c
>> > @@ -915,7 +915,7 @@ 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;
>> > +bool rodata_enabled = true;
>> 
>> Is there a mismatch here between the extern ifdef and the bool ifdef?
>> I.e. shouldn't the ifdef here be || DEBUG_SET_MODULE_RONX too?
>
> Yes.
>
>> Also, can you mark this as __ro_after_init, since nothing changes it
>> after the kernel command line is parsed?
>
> Yes, yes.
>
> Thanks,
> -Takahiro AKASHI
>
>> Otherwise, this looks fine to me.
>> 
>> -Kees
>> 
>> 
>> -- 
>> Kees Cook
>> Nexus Security
AKASHI Takahiro Oct. 26, 2016, 4:43 a.m. UTC | #4
Rusty, Jessica

On Wed, Oct 26, 2016 at 10:43:32AM +1030, Rusty Russell wrote:
> AKASHI Takahiro <takahiro.akashi@linaro.org> writes:
> > On Thu, Oct 20, 2016 at 01:48:15PM -0700, Kees Cook wrote:
> >> On Wed, Oct 19, 2016 at 11:24 PM, AKASHI Takahiro
> >> <takahiro.akashi@linaro.org> wrote:
> >> > 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 patch looks good (except the minor issues noted by Kees); please CC
> the followup version to Jessica as new module maintainer.

I think that the new version (v2)[1] addresses Kees' comments already.

[1] http://lkml.iu.edu//hypermail/linux/kernel/1610.2/04163.html

Thanks,
-Takahiro AKASHI

> Thanks!
> Rusty.
> 
> >> >
> >> > 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: Mark Rutland <mark.rutland@arm.com>
> >> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> >> > Cc: Rusty Russell <rusty@rustcorp.com.au>
> >> > ---
> >> > 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          |  2 +-
> >> >  kernel/module.c      | 21 ++++++++++++++++++---
> >> >  3 files changed, 21 insertions(+), 5 deletions(-)
> >> >
> >> > diff --git a/include/linux/init.h b/include/linux/init.h
> >> > index e30104c..20aa2eb 100644
> >> > --- a/include/linux/init.h
> >> > +++ b/include/linux/init.h
> >> > @@ -126,7 +126,8 @@ void prepare_namespace(void);
> >> >  void __init load_default_modules(void);
> >> >  int __init init_rootfs(void);
> >> >
> >> > -#ifdef CONFIG_DEBUG_RODATA
> >> > +#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_DEBUG_SET_MODULE_RONX)
> >> > +extern bool rodata_enabled;
> >> >  void mark_rodata_ro(void);
> >> >  #endif
> >> >
> >> > diff --git a/init/main.c b/init/main.c
> >> > index 2858be7..92db2f3 100644
> >> > --- a/init/main.c
> >> > +++ b/init/main.c
> >> > @@ -915,7 +915,7 @@ 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;
> >> > +bool rodata_enabled = true;
> >> 
> >> Is there a mismatch here between the extern ifdef and the bool ifdef?
> >> I.e. shouldn't the ifdef here be || DEBUG_SET_MODULE_RONX too?
> >
> > Yes.
> >
> >> Also, can you mark this as __ro_after_init, since nothing changes it
> >> after the kernel command line is parsed?
> >
> > Yes, yes.
> >
> > Thanks,
> > -Takahiro AKASHI
> >
> >> Otherwise, this looks fine to me.
> >> 
> >> -Kees
> >> 
> >> 
> >> -- 
> >> Kees Cook
> >> Nexus Security

Patch
diff mbox

diff --git a/include/linux/init.h b/include/linux/init.h
index e30104c..20aa2eb 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -126,7 +126,8 @@  void prepare_namespace(void);
 void __init load_default_modules(void);
 int __init init_rootfs(void);
 
-#ifdef CONFIG_DEBUG_RODATA
+#if defined(CONFIG_DEBUG_RODATA) || defined(CONFIG_DEBUG_SET_MODULE_RONX)
+extern bool rodata_enabled;
 void mark_rodata_ro(void);
 #endif
 
diff --git a/init/main.c b/init/main.c
index 2858be7..92db2f3 100644
--- a/init/main.c
+++ b/init/main.c
@@ -915,7 +915,7 @@  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;
+bool rodata_enabled = true;
 static int __init set_debug_rodata(char *str)
 {
 	return strtobool(str, &rodata_enabled);
diff --git a/kernel/module.c b/kernel/module.c
index f57dd63..34d1880 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 +1992,13 @@  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_rodata(layout, set_memory_x);
-	frob_ro_after_init(layout, set_memory_rw);
+	if (rodata_enabled)
+		frob_ro_after_init(layout, set_memory_rw);
 	frob_ro_after_init(layout, set_memory_x);
 	frob_writable_data(layout, set_memory_x);
 }