Commit 9dd721c6 authored Mar 10, 2014 by Kees Cook Committed by H. Peter Anvin Mar 24, 2014

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 <fengguang.wu@intel.com>
Signed-off-by: Andy Honig <ahonig@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

parent e2b32e67

arch/x86/kernel/module.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

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