Commit 94462ad3 authored Nov 29, 2010 by Steven Rostedt

module: Move RO/NX module protection to after ftrace module update



The commit:

84e1c6bb
x86: Add RO/NX protection for loadable kernel modules

Broke the function tracer with this output:

------------[ 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]

The cause was that the module text was set to read only before ftrace
could convert the calls to mcount to nops. Thus, the conversions failed
due to not being able to write to the text locations.

The simple fix is to move setting the module to read only after the
module notifiers are called (where ftrace sets the module mcounts to nops).

Reported-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent 26e20a10

kernel/module.c

+12 −12

Original line number	Diff line number	Diff line
		@@ -2816,18 +2816,6 @@ 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;
		@@ -2888,6 +2876,18 @@ 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)

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