Subject: Re: [PATCH 3/3 V13] RO/NX protection for loadable kernel

From: mat <[email-masked]>
Date: Tue, 30 Nov 2010 22:20:25 +0100

Hi,

Le Mon, 29 Nov 2010 13:15:42 -0500,
Steven Rostedt <[email-masked]> a écrit :

> This patch breaks function tracer:
> 
> ------------[ cut here ]------------
> WARNING: at kernel/trace/ftrace.c:1014 ftrace_bug+0x114/0x171()
> Hardware name: Precision WorkStation 470    
> Modules linked in: i2c_core(+)
> Pid: 86, comm: modprobe Not tainted 2.6.37-rc2+ #68
> Call Trace:
>  [<ffffffff8104e957>] warn_slowpath_common+0x85/0x9d
>  [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
>  [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
>  [<ffffffff8104e989>] warn_slowpath_null+0x1a/0x1c
>  [<ffffffff810a9dfe>] ftrace_bug+0x114/0x171
>  [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
>  [<ffffffff810aa0db>] ftrace_process_locs+0x1ae/0x274
>  [<ffffffffa00026db>] ? __process_new_adapter+0x7/0x34 [i2c_core]
>  [<ffffffff810aa29e>] ftrace_module_notify+0x39/0x44
>  [<ffffffff814405cf>] notifier_call_chain+0x37/0x63
>  [<ffffffff8106e054>] __blocking_notifier_call_chain+0x46/0x5b
>  [<ffffffff8106e07d>] blocking_notifier_call_chain+0x14/0x16
>  [<ffffffff8107ffde>] sys_init_module+0x73/0x1f3
>  [<ffffffff8100acf2>] system_call_fastpath+0x16/0x1b
> ---[ end trace 2aff4f4ca53ec746 ]---
> ftrace faulted on writing [<ffffffffa00026db>]
> __process_new_adapter+0x7/0x34 [i2c_core]
> 
> 
> On Tue, Nov 16, 2010 at 10:35:16PM +0100, matthieu castet wrote:
> >  
> > @@ -2650,6 +2810,18 @@ static struct module *load_module(void
> > __user *umod, kfree(info.strmap);
> >  	free_copy(&info);
> >  
> > +	/* Set RO and NX regions for core */
> > +	set_section_ro_nx(mod->module_core,
> > +				mod->core_text_size,
> > +				mod->core_ro_size,
> > +				mod->core_size);
> > +
> > +	/* Set RO and NX regions for init */
> > +	set_section_ro_nx(mod->module_init,
> > +				mod->init_text_size,
> > +				mod->init_ro_size,
> > +				mod->init_size);
> > +
> 
> Here we set the text read only before we call the notifiers. The
> function tracer changes the calls to mcount into nops via a notifier
> call so this must be done after the module notifiers.
> 
> >  	/* Done! */
> >  	trace_module_load(mod);
> >  	return mod;
> > @@ -2753,6 +2925,7 @@ SYSCALL_DEFINE3(init_module, void __user *,
> > umod, mod->symtab = mod->core_symtab;
> >  	mod->strtab = mod->core_strtab;
> >  #endif
> > +	unset_section_ro_nx(mod, mod->module_init);
> >  	module_free(mod, mod->module_init);
> >  	mod->module_init = NULL;
> >  	mod->init_size = 0;
> 
> Below is the patch that fixes this bug.
> 
> -- Steve
> 
> Reported-by: Peter Zijlstra <[email-masked]>
> Signed-off-by: Steven Rostedt <[email-masked]>
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index ba421e6..5ccf52c 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2804,18 +2804,6 @@ static struct module *load_module(void __user
> *umod, kfree(info.strmap);
>  	free_copy(&info);
>  
> -	/* Set RO and NX regions for core */
> -	set_section_ro_nx(mod->module_core,
> -				mod->core_text_size,
> -				mod->core_ro_size,
> -				mod->core_size);
> -
> -	/* Set RO and NX regions for init */
> -	set_section_ro_nx(mod->module_init,
> -				mod->init_text_size,
> -				mod->init_ro_size,
> -				mod->init_size);
> -
>  	/* Done! */
>  	trace_module_load(mod);
>  	return mod;
> @@ -2876,6 +2864,18 @@ SYSCALL_DEFINE3(init_module, void __user *,
> umod, blocking_notifier_call_chain(&module_notify_list,
>  			MODULE_STATE_COMING, mod);
>  
> +	/* Set RO and NX regions for core */
> +	set_section_ro_nx(mod->module_core,
> +				mod->core_text_size,
> +				mod->core_ro_size,
> +				mod->core_size);
> +
> +	/* Set RO and NX regions for init */
> +	set_section_ro_nx(mod->module_init,
> +				mod->init_text_size,
> +				mod->init_ro_size,
> +				mod->init_size);
> +
>  	do_mod_ctors(mod);
>  	/* Start the module */
>  	if (mod->init != NULL)
> 
> 

That's look fine for me.

But I wonder why ftrace_arch_code_modify_prepare isn't called ?

It is only called when we start/stop tracing ?

Matthieu