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SubjectRe: [PATCH 3/3 V13] RO/NX protection for loadable kernel
Hi,

Le Mon, 29 Nov 2010 13:15:42 -0500,
Steven Rostedt <rostedt@goodmis.org> 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 <a.p.zijlstra@chello.nl>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
>
> 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
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