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* [PATCH] module: make module symbols visible after init
@ 2020-06-03 14:12 Cheng Jian
  2020-06-03 17:00 ` Miroslav Benes
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: Cheng Jian @ 2020-06-03 14:12 UTC (permalink / raw)
  To: linux-kernel, live-patching
  Cc: cj.chengjian, chenwandun, xiexiuqi, bobo.shaobowang,
	huawei.libin, jeyu, jikos

When lookup the symbols of module by module_kallsyms_lookup_name(),
the symbols address is visible only if the module's status isn't
MODULE_STATE_UNFORMED, This is problematic.

When complete_formation is done, the state of the module is modified
to MODULE_STATE_COMING, and the symbol of module is visible to the

At this time, the init function of the module has not been called,
so if the address of the function symbol has been found and called,
it may cause some exceptions.

For livepatch module, the relocation information of the livepatch
module is completed in init by klp_write_object_relocations(), and
the symbol name of the old and new functions are the same. Therefore,
when we lookup the symbol, we may get the function address of the
livepatch module. a crash can occurs when we call this function.

	CPU 0				CPU 1
	add_unformed_module # MODULE_STATE_UNFORMED;
	complete_formation  # MODULE_STATE_COMING;
					call A()	# CRASH
	mod->state = MODULE_STATE_LIVE;

In commit 0bd476e6c671 ("kallsyms: unexport kallsyms_lookup_name() and
kallsyms_on_each_symbol()") restricts the invocation for kernel unexported
symbols, but it is still incorrect to make the symbols of non-LIVE modules
visible to the outside.

Signed-off-by: Cheng Jian <>
 kernel/module.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/module.c b/kernel/module.c
index 64a2b4daaaa5..96c9cb64de57 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4220,7 +4220,7 @@ unsigned long module_kallsyms_lookup_name(const char *name)
 			ret = find_kallsyms_symbol_value(mod, colon+1);
 	} else {
 		list_for_each_entry_rcu(mod, &modules, list) {
-			if (mod->state == MODULE_STATE_UNFORMED)
+			if (mod->state != MODULE_STATE_LIVE)
 			if ((ret = find_kallsyms_symbol_value(mod, name)) != 0)

^ permalink raw reply related	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2020-06-04 12:56 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-06-03 14:12 [PATCH] module: make module symbols visible after init Cheng Jian
2020-06-03 17:00 ` Miroslav Benes
2020-06-04  9:49   ` Jessica Yu
2020-06-04  8:57 ` Petr Mladek
2020-06-04 12:55 ` chengjian (D)

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