module: Restore the moduleparam prefix length check

The moduleparam code allows modules to provide their own definition of
MODULE_PARAM_PREFIX, instead of using the default KBUILD_MODNAME ".".

Commit 730b69d ("module: check kernel param length at compile time,
not runtime") added a check to ensure the prefix doesn't exceed
MODULE_NAME_LEN, as this is what param_sysfs_builtin() expects.

Later, commit 58f86cc ("VERIFY_OCTAL_PERMISSIONS: stricter checking
for sysfs perms.") removed this check, but there is no indication this was
intentional.

Since the check is still useful for param_sysfs_builtin() to function
properly, reintroduce it in __module_param_call(), but in a modernized form
using static_assert().

While here, clean up the __module_param_call() comments. In particular,
remove the comment "Default value instead of permissions?", which comes
from commit 9774a1f ("[PATCH] Compile-time check re world-writeable
module params"). This comment was related to the test variable
__param_perm_check_##name, which was removed in the previously mentioned
commit 58f86cc.

Fixes: 58f86cc ("VERIFY_OCTAL_PERMISSIONS: stricter checking for sysfs perms.")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Daniel Gomez <da.gomez@samsung.com>
Link: https://lore.kernel.org/r/20250630143535.267745-4-petr.pavlu@suse.com
Signed-off-by: Daniel Gomez <da.gomez@samsung.com>

Author: petrpavlu

include/linux/moduleparam.h

@@ -282,10 +282,9 @@ struct kparam_array
 #define __moduleparam_const const
 #endif
 
-/* This is the fundamental function for registering boot/module
-   parameters. */
+/* This is the fundamental function for registering boot/module parameters. */
 #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
-	/* Default value instead of permissions? */			\
+	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\
 	static const char __param_str_##name[] = prefix #name;		\
 	static struct kernel_param __moduleparam_const __param_##name	\
 	__used __section("__param")					\