Re: [RFC PATCH 2/2] module: When modifying a module's text ignore modules which are going away too

[Steven Rostedt]

On Wed, 26 Oct 2016 11:35:18 +1030
Rusty Russell  wrote:

> Aaron Tomlin  writes:
> > By default, during the access permission modification of a module's core
> > and init pages, we only ignore modules that are malformed. There is no
> > reason not to extend this to modules which are going away too.  
> 
> Well, it depends on all the callers (ie. ftrace): is that also ignoring
> modules which are going away?
> 
> Otherwise, we set MODULE_STATE_GOING, ftrace walks all the modules and
> this one is still RO...
> 

Actually, looking into this more, you are correct. There's a
possibility in enabling ftrace after the module is about to go but
before ftrace_release_mod() is called (which will remove the module
text from the ftrace function list).

I don't see any reason for not allowing set_all_modules_text_rw() from
being called if a module is going. If a module is going, shouldn't its
text be rw anyway?

Perhaps just preventing it from turning into ro will be sufficient. And
remove the check from set_all_modules_text_rw().

-- Steve


> Thanks,
> Rusty.
> 
> > This patch makes both set_all_modules_text_rw() and
> > set_all_modules_text_ro() skip modules which are going away too.
> >
> > Signed-off-by: Aaron Tomlin 
> > ---
> >  kernel/module.c | 6 --
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index ff93ab8..09c386b 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -1953,7 +1953,8 @@ void set_all_modules_text_rw(void)
> >  
> > mutex_lock(_mutex);
> > list_for_each_entry_rcu(mod, , list) {
> > -   if (mod->state == MODULE_STATE_UNFORMED)
> > +   if (mod->state == MODULE_STATE_UNFORMED ||
> > +   mod->state == MODULE_STATE_GOING)
> > continue;
> >  
> > frob_text(>core_layout, set_memory_rw);
> > @@ -1969,7 +1970,8 @@ void set_all_modules_text_ro(void)
> >  
> > mutex_lock(_mutex);
> > list_for_each_entry_rcu(mod, , list) {
> > -   if (mod->state == MODULE_STATE_UNFORMED)
> > +   if (mod->state == MODULE_STATE_UNFORMED ||
> > +   mod->state == MODULE_STATE_GOING)
> > continue;
> >  
> > frob_text(>core_layout, set_memory_ro);
> > -- 
> > 2.5.5  

Re: [RFC PATCH 2/2] module: When modifying a module's text ignore modules which are going away too

[Steven Rostedt]

On Wed, 26 Oct 2016 11:35:18 +1030
Rusty Russell  wrote:

> Aaron Tomlin  writes:
> > By default, during the access permission modification of a module's core
> > and init pages, we only ignore modules that are malformed. There is no
> > reason not to extend this to modules which are going away too.  
> 
> Well, it depends on all the callers (ie. ftrace): is that also ignoring
> modules which are going away?
> 
> Otherwise, we set MODULE_STATE_GOING, ftrace walks all the modules and
> this one is still RO...
> 

Actually, looking into this more, you are correct. There's a
possibility in enabling ftrace after the module is about to go but
before ftrace_release_mod() is called (which will remove the module
text from the ftrace function list).

I don't see any reason for not allowing set_all_modules_text_rw() from
being called if a module is going. If a module is going, shouldn't its
text be rw anyway?

Perhaps just preventing it from turning into ro will be sufficient. And
remove the check from set_all_modules_text_rw().

-- Steve


> Thanks,
> Rusty.
> 
> > This patch makes both set_all_modules_text_rw() and
> > set_all_modules_text_ro() skip modules which are going away too.
> >
> > Signed-off-by: Aaron Tomlin 
> > ---
> >  kernel/module.c | 6 --
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index ff93ab8..09c386b 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -1953,7 +1953,8 @@ void set_all_modules_text_rw(void)
> >  
> > mutex_lock(_mutex);
> > list_for_each_entry_rcu(mod, , list) {
> > -   if (mod->state == MODULE_STATE_UNFORMED)
> > +   if (mod->state == MODULE_STATE_UNFORMED ||
> > +   mod->state == MODULE_STATE_GOING)
> > continue;
> >  
> > frob_text(>core_layout, set_memory_rw);
> > @@ -1969,7 +1970,8 @@ void set_all_modules_text_ro(void)
> >  
> > mutex_lock(_mutex);
> > list_for_each_entry_rcu(mod, , list) {
> > -   if (mod->state == MODULE_STATE_UNFORMED)
> > +   if (mod->state == MODULE_STATE_UNFORMED ||
> > +   mod->state == MODULE_STATE_GOING)
> > continue;
> >  
> > frob_text(>core_layout, set_memory_ro);
> > -- 
> > 2.5.5  

Re: [RFC PATCH 2/2] module: When modifying a module's text ignore modules which are going away too

[Rusty Russell]

Aaron Tomlin  writes:
> By default, during the access permission modification of a module's core
> and init pages, we only ignore modules that are malformed. There is no
> reason not to extend this to modules which are going away too.

Well, it depends on all the callers (ie. ftrace): is that also ignoring
modules which are going away?

Otherwise, we set MODULE_STATE_GOING, ftrace walks all the modules and
this one is still RO...

Thanks,
Rusty.

> This patch makes both set_all_modules_text_rw() and
> set_all_modules_text_ro() skip modules which are going away too.
>
> Signed-off-by: Aaron Tomlin 
> ---
>  kernel/module.c | 6 --
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index ff93ab8..09c386b 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1953,7 +1953,8 @@ void set_all_modules_text_rw(void)
>  
>   mutex_lock(_mutex);
>   list_for_each_entry_rcu(mod, , list) {
> - if (mod->state == MODULE_STATE_UNFORMED)
> + if (mod->state == MODULE_STATE_UNFORMED ||
> + mod->state == MODULE_STATE_GOING)
>   continue;
>  
>   frob_text(>core_layout, set_memory_rw);
> @@ -1969,7 +1970,8 @@ void set_all_modules_text_ro(void)
>  
>   mutex_lock(_mutex);
>   list_for_each_entry_rcu(mod, , list) {
> - if (mod->state == MODULE_STATE_UNFORMED)
> + if (mod->state == MODULE_STATE_UNFORMED ||
> + mod->state == MODULE_STATE_GOING)
>   continue;
>  
>   frob_text(>core_layout, set_memory_ro);
> -- 
> 2.5.5

Re: [RFC PATCH 2/2] module: When modifying a module's text ignore modules which are going away too

[Rusty Russell]

Aaron Tomlin  writes:
> By default, during the access permission modification of a module's core
> and init pages, we only ignore modules that are malformed. There is no
> reason not to extend this to modules which are going away too.

Well, it depends on all the callers (ie. ftrace): is that also ignoring
modules which are going away?

Otherwise, we set MODULE_STATE_GOING, ftrace walks all the modules and
this one is still RO...

Thanks,
Rusty.

> This patch makes both set_all_modules_text_rw() and
> set_all_modules_text_ro() skip modules which are going away too.
>
> Signed-off-by: Aaron Tomlin 
> ---
>  kernel/module.c | 6 --
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index ff93ab8..09c386b 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1953,7 +1953,8 @@ void set_all_modules_text_rw(void)
>  
>   mutex_lock(_mutex);
>   list_for_each_entry_rcu(mod, , list) {
> - if (mod->state == MODULE_STATE_UNFORMED)
> + if (mod->state == MODULE_STATE_UNFORMED ||
> + mod->state == MODULE_STATE_GOING)
>   continue;
>  
>   frob_text(>core_layout, set_memory_rw);
> @@ -1969,7 +1970,8 @@ void set_all_modules_text_ro(void)
>  
>   mutex_lock(_mutex);
>   list_for_each_entry_rcu(mod, , list) {
> - if (mod->state == MODULE_STATE_UNFORMED)
> + if (mod->state == MODULE_STATE_UNFORMED ||
> + mod->state == MODULE_STATE_GOING)
>   continue;
>  
>   frob_text(>core_layout, set_memory_ro);
> -- 
> 2.5.5