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>

1 files changed, 7 insertions, 22 deletions

diff --git a/kernel/panic.c b/kernel/panic.c
index 28153aec710..87445a894c3 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;
 }
 /*