1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * GCC stack protector support.
4  *
5  * Stack protector works by putting predefined pattern at the start of
6  * the stack frame and verifying that it hasn't been overwritten when
7  * returning from the function.  The pattern is called stack canary
8  * and gcc expects it to be defined by a global variable called
9  * "__stack_chk_guard" on ARM.  This unfortunately means that on SMP
10  * we cannot have a different canary value per task.
11  */
12 
13 #ifndef __ASM_STACKPROTECTOR_H
14 #define __ASM_STACKPROTECTOR_H
15 
16 #include <linux/random.h>
17 #include <linux/version.h>
18 
19 extern unsigned long __stack_chk_guard;
20 
21 /*
22  * Initialize the stackprotector canary value.
23  *
24  * NOTE: this must only be called from functions that never return,
25  * and it must always be inlined.
26  */
27 static __always_inline void boot_init_stack_canary(void)
28 {
29 	unsigned long canary;
30 
31 	/* Try to get a semi random initial value. */
32 	get_random_bytes(&canary, sizeof(canary));
33 	canary ^= LINUX_VERSION_CODE;
34 	canary &= CANARY_MASK;
35 
36 	current->stack_canary = canary;
37 	if (!IS_ENABLED(CONFIG_STACKPROTECTOR_PER_TASK))
38 		__stack_chk_guard = current->stack_canary;
39 }
40 
41 #endif	/* _ASM_STACKPROTECTOR_H */
42