x86, kaslr: fix module lock ordering problem

There was a potential lock ordering problem with the module kASLR patch ("x86, kaslr: randomize module base load address"). This patch removes the usage of the module_mutex and creates a new mutex to protect the module base address offset value. Chain exists of: text_mutex --> kprobe_insn_slots.mutex --> module_mutex [ 0.515561] Possible unsafe locking scenario: [ 0.515561] [ 0.515561] CPU0 CPU1 [ 0.515561] ---- ---- [ 0.515561] lock(module_mutex); [ 0.515561] lock(kprobe_insn_slots.mutex); [ 0.515561] lock(module_mutex); [ 0.515561] lock(text_mutex); [ 0.515561] [ 0.515561] *** DEADLOCK *** Reported-by: Fengguang Wu <[email protected]> Signed-off-by: Andy Honig <[email protected]> Signed-off-by: Kees Cook <[email protected]> Reviewed-by: Masami Hiramatsu <[email protected]> Signed-off-by: H. Peter Anvin <[email protected]>
AnTAVR · Mar 24, 2014 · 9dd721c · 9dd721c
1 parent e2b32e6
commit 9dd721c
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
@@ -48,6 +48,9 @@ do {							\
 static unsigned long module_load_offset;
 static int randomize_modules = 1;
 
+/* Mutex protects the module_load_offset. */
+static DEFINE_MUTEX(module_kaslr_mutex);
+
 static int __init parse_nokaslr(char *p)
 {
 	randomize_modules = 0;
@@ -58,7 +61,7 @@ early_param("nokaslr", parse_nokaslr);
 static unsigned long int get_module_load_offset(void)
 {
 	if (randomize_modules) {
-		mutex_lock(&module_mutex);
+		mutex_lock(&module_kaslr_mutex);
 		/*
 		 * Calculate the module_load_offset the first time this
 		 * code is called. Once calculated it stays the same until
@@ -67,7 +70,7 @@ static unsigned long int get_module_load_offset(void)
 		if (module_load_offset == 0)
 			module_load_offset =
 				(get_random_int() % 1024 + 1) * PAGE_SIZE;
-		mutex_unlock(&module_mutex);
+		mutex_unlock(&module_kaslr_mutex);
 	}
 	return module_load_offset;
 }