From af9ff7868f0f76d3364351b1641b9dfa99588e77 Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@linux.intel.com>
Date: Sat, 12 Jul 2008 09:36:38 -0700
Subject: x86: simplify stackprotector self-check

Clean up the code by removing no longer needed code;
make sure the pda is updated and kept in sync

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/asm-x86/pda.h b/include/asm-x86/pda.h
index 62b7349..a5ff5bb 100644
--- a/include/asm-x86/pda.h
+++ b/include/asm-x86/pda.h
@@ -131,4 +131,5 @@ do {									\
 
 #define PDA_STACKOFFSET (5*8)
 
+#define refresh_stack_canary() write_pda(stack_canary, current->stack_canary)
 #endif
diff --git a/kernel/panic.c b/kernel/panic.c
index 28153ae..87445a8 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -328,37 +328,21 @@ EXPORT_SYMBOL(warn_on_slowpath);
 #ifndef GCC_HAS_SP
 #warning You have selected the CONFIG_CC_STACKPROTECTOR option, but the gcc used does not support this.
 #endif
+
 static unsigned long __stack_check_testing;
+
 /*
  * Self test function for the stack-protector feature.
  * This test requires that the local variable absolutely has
- * a stack slot, hence the barrier()s.
+ * a stack slot.
  */
 static noinline void __stack_chk_test_func(void)
 {
-	unsigned long foo;
-	barrier();
-	/*
-	 * we need to make sure we're not about to clobber the return address,
-	 * while real exploits do this, it's unhealthy on a running system.
-	 * Besides, if we would, the test is already failed anyway so
-	 * time to pull the emergency brake on it.
-	 */
-	if ((unsigned long)__builtin_return_address(0) ==
-					*(((unsigned long *)&foo)+1)) {
-		printk(KERN_ERR "No -fstack-protector-stack-frame!\n");
-	}
-#ifdef CONFIG_FRAME_POINTER
-	/* We also don't want to clobber the frame pointer */
-	if ((unsigned long)__builtin_return_address(0) ==
-					*(((unsigned long *)&foo)+2)) {
-		printk(KERN_ERR "No -fstack-protector-stack-frame!\n");
-	}
-#endif
-	if (current->stack_canary != *(((unsigned long *)&foo)+1))
-		printk(KERN_ERR "No -fstack-protector canary found\n");
+	unsigned long dummy_buffer[64]; /* force gcc to use the canary */
 
 	current->stack_canary = ~current->stack_canary;
+	refresh_stack_canary();
+	dummy_buffer[3] = 1; /* fool gcc into keeping the variable */
 }
 
 static int __stack_chk_test(void)
@@ -371,6 +355,7 @@ static int __stack_chk_test(void)
 		WARN_ON(1);
 	};
 	current->stack_canary = ~current->stack_canary;
+	refresh_stack_canary();
 	return 0;
 }
 /*
-- 
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