From 1cf6e1d28e69ae933e674af0003bdcf995e07a32 Mon Sep 17 00:00:00 2001
From: Mukesh Ojha <mojha@codeaurora.org>
Date: Fri, 22 Jun 2018 16:59:47 +0530
Subject: [PATCH] Kconfig.debug: module: Add debug config to debug modules

There can be scenario where, dynamically loadable modules adds
a certain nodes in list data structure and forgot to remove
reference from the list while unloading themself. And this can
result in fault while accessing those dangling pointers.

So If we log the module used address ranges, we could be able to
tell exact victim module.

And, It will be good to keep these debug logs under a config flag.

So, let's add DEBUG_MODULE_LOAD_INFO config and use this in
printing module used init and core layout address
ranges.

e.g:
Core layout sections:
[   40.599573]  .text
[   40.627074]  .plt
[   40.603426]  .rodata.str1.8
[   40.608016]  __mcount_loc
[   40.622142]  .note.gnu.build-id
[   40.612654]  .data
[   40.616438]  .gnu.linkonce.this_module
[   40.634909]  .bss

Init layout sections
[   40.630781]  .init.plt
[   40.638591]  .symtab
[   40.642573]  .strtab

After this patch:
/ # insmod sample.ko
[   26.244768] Hi Mukesh
[   26.247314] Loaded sample: module init layout addresses range: 0xffffff9dbff8a000-0xffffff9dbff8bfff
[   26.256896] sample: core layout addresses range: 0xffffff9dbff85000-0xffffff9dbff88fff
/ # rmmod sample
[   63.812065] Bye Mukesh
[   63.816318] Unloaded sample: module core layout address range: 0xffffff9dbff85000-0xffffff9dbff88fff

Change-Id: I4acfc4f53c561f92ca63fa3c4559148929575580
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
---
 kernel/module.c   | 13 +++++++++++++
 lib/Kconfig.debug | 12 ++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/kernel/module.c b/kernel/module.c
index d89d348f185c..52d106d463e9 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2178,6 +2178,11 @@ static void free_module(struct module *mod)
 
 	/* Finally, free the core (containing the module structure) */
 	disable_ro_nx(&mod->core_layout);
+#ifdef CONFIG_DEBUG_MODULE_LOAD_INFO
+	pr_info("Unloaded %s: module core layout address range: 0x%lx-0x%lx\n",
+		mod->name, (long)mod->core_layout.base,
+		(long)(mod->core_layout.base + mod->core_layout.size - 1));
+#endif
 	module_memfree(mod->core_layout.base);
 
 #ifdef CONFIG_MPU
@@ -3507,6 +3512,14 @@ static noinline int do_init_module(struct module *mod)
 	mod_tree_remove_init(mod);
 	disable_ro_nx(&mod->init_layout);
 	module_arch_freeing_init(mod);
+#ifdef CONFIG_DEBUG_MODULE_LOAD_INFO
+	pr_info("Loaded %s: module init layout addresses range: 0x%lx-0x%lx\n",
+		mod->name, (long)mod->init_layout.base,
+		(long)(mod->init_layout.base + mod->init_layout.size - 1));
+	pr_info("%s: core layout addresses range: 0x%lx-0x%lx\n", mod->name,
+		(long)mod->core_layout.base,
+		(long)(mod->core_layout.base + mod->core_layout.size - 1));
+#endif
 	mod->init_layout.base = NULL;
 	mod->init_layout.size = 0;
 	mod->init_layout.ro_size = 0;
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 40f399a8eda3..d87c2fa56ed5 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -133,6 +133,18 @@ config DYNAMIC_DEBUG
 	  See Documentation/admin-guide/dynamic-debug-howto.rst for additional
 	  information.
 
+config DEBUG_MODULE_LOAD_INFO
+        bool "Use prints for module info under a debug flag"
+	help
+	  If you say Y here the resulting kernel image will include
+          debug prints which was kept under DEBUG_MODULE_LOAD_INFO.
+          This will be used by developer to debug loadable modules in
+	  the kernel.
+	  Say Y here only if you plan to debug the kernel.
+
+	  If unsure, say N.
+
+
 endmenu # "printk and dmesg options"
 
 menu "Compile-time checks and compiler options"