search_module_extables() returns an exception_table_entry belonging to a
module. The lookup via __module_address() can be performed with RCU
protection.
The returned exception_table_entry remains valid because the passed
address usually belongs to a module that is currently executed. So the
module can not be removed because "something else" holds a reference to
it, ensuring that it can not be removed.
Exceptions here are:
- kprobe, acquires a reference on the module beforehand
- MCE, invokes the function from within a timer and the RCU lifetime
guarantees (of the timer) are sufficient.
Therefore it is safe to return the exception_table_entry outside the RCU
section which provided the module.
Use RCU for the lookup in search_module_extables() and update the
comment.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
kernel/module/main.c | 23 +++++++++--------------
1 file changed, 9 insertions(+), 14 deletions(-)
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 686b74c7c17f5..74b9e9ddb4b65 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -3621,28 +3621,23 @@ char *module_flags(struct module *mod, char *buf, bool show_state)
/* Given an address, look for it in the module exception tables. */
const struct exception_table_entry *search_module_extables(unsigned long addr)
{
- const struct exception_table_entry *e = NULL;
struct module *mod;
- preempt_disable();
+ guard(rcu)();
mod = __module_address(addr);
if (!mod)
- goto out;
+ return NULL;
if (!mod->num_exentries)
- goto out;
-
- e = search_extable(mod->extable,
- mod->num_exentries,
- addr);
-out:
- preempt_enable();
-
+ return NULL;
/*
- * Now, if we found one, we are running inside it now, hence
- * we cannot unload the module, hence no refcnt needed.
+ * The address passed here belongs to a module that is currently
+ * invoked (we are running inside it). Therefore its module::refcnt
+ * needs already be >0 to ensure that it is not removed at this stage.
+ * All other user need to invoke this function within a RCU read
+ * section.
*/
- return e;
+ return search_extable(mod->extable, mod->num_exentries, addr);
}
/**
--
2.45.2
