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 prevents SMP systems from using a
10  * different value for each task unless we enable a GCC plugin that
11  * replaces these symbol references with references to each task's own
12  * value.
13  */
14 
15 #ifndef _ASM_STACKPROTECTOR_H
16 #define _ASM_STACKPROTECTOR_H 1
17 
18 #include <linux/random.h>
19 #include <linux/version.h>
20 
21 #include <asm/thread_info.h>
22 
23 extern unsigned long __stack_chk_guard;
24 
25 /*
26  * Initialize the stackprotector canary value.
27  *
28  * NOTE: this must only be called from functions that never return,
29  * and it must always be inlined.
30  */
31 static __always_inline void boot_init_stack_canary(void)
32 {
33 	unsigned long canary;
34 
35 	/* Try to get a semi random initial value. */
36 	get_random_bytes(&canary, sizeof(canary));
37 	canary ^= LINUX_VERSION_CODE;
38 
39 	current->stack_canary = canary;
40 #ifndef CONFIG_STACKPROTECTOR_PER_TASK
41 	__stack_chk_guard = current->stack_canary;
42 #else
43 	current_thread_info()->stack_canary = current->stack_canary;
44 #endif
45 }
46 
47 #endif	/* _ASM_STACKPROTECTOR_H */
48