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x86: add CONFIG_CC_STACKPROTECTOR self-test

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This patch adds a simple self-test capability to the stackprotector
feature. The test deliberately overflows a stack buffer and then
checks if the canary trap function gets called.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Arjan van de Ven 2008-02-15 15:33:12 -08:00 committed by Thomas Gleixner
parent 113c5413cf
commit 54371a43a6
1 changed files with 68 additions and 0 deletions
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68
kernel/panic.c
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@ -324,14 +324,82 @@ EXPORT_SYMBOL(warn_on_slowpath);
#endif
#ifdef CONFIG_CC_STACKPROTECTOR
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.
*/
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");
return;
}
#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");
return;
}
#endif
barrier();
if (current->stack_canary == *(((unsigned long *)&foo)+1))
*(((unsigned long *)&foo)+1) = 0;
else
printk(KERN_ERR "No -fstack-protector canary found\n");
barrier();
}
static int __stack_chk_test(void)
{
printk(KERN_INFO "Testing -fstack-protector-all feature\n");
__stack_check_testing = (unsigned long)&__stack_chk_test_func;
__stack_chk_test_func();
if (__stack_check_testing) {
printk(KERN_ERR "-fstack-protector-all test failed\n");
WARN_ON(1);
}
return 0;
}
/*
* Called when gcc's -fstack-protector feature is used, and
* gcc detects corruption of the on-stack canary value
*/
void __stack_chk_fail(void)
{
if (__stack_check_testing == (unsigned long)&__stack_chk_test_func) {
long delta;
delta = (unsigned long)__builtin_return_address(0) -
__stack_check_testing;
/*
* The test needs to happen inside the test function, so
* check if the return address is close to that function.
* The function is only 2 dozen bytes long, but keep a wide
* safety margin to avoid panic()s for normal users regardless
* of the quality of the compiler.
*/
if (delta >= 0 && delta <= 400) {
__stack_check_testing = 0;
return;
}
}
panic("stack-protector: Kernel stack is corrupted in: %p\n",
__builtin_return_address(0));
}
EXPORT_SYMBOL(__stack_chk_fail);
late_initcall(__stack_chk_test);
#endif