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 #include <asm/pointer_auth.h>
19 
20 extern unsigned long __stack_chk_guard;
21 
22 /*
23  * Initialize the stackprotector canary value.
24  *
25  * NOTE: this must only be called from functions that never return,
26  * and it must always be inlined.
27  */
28 static __always_inline void boot_init_stack_canary(void)
29 {
30 #if defined(CONFIG_STACKPROTECTOR)
31 	unsigned long canary;
32 
33 	/* Try to get a semi random initial value. */
34 	get_random_bytes(&canary, sizeof(canary));
35 	canary ^= LINUX_VERSION_CODE;
36 	canary &= CANARY_MASK;
37 
38 	current->stack_canary = canary;
39 	if (!IS_ENABLED(CONFIG_STACKPROTECTOR_PER_TASK))
40 		__stack_chk_guard = current->stack_canary;
41 #endif
42 	ptrauth_thread_init_kernel(current);
43 	ptrauth_thread_switch_kernel(current);
44 }
45 
46 #endif	/* _ASM_STACKPROTECTOR_H */
47