1 #ifndef _ASM_STACKPROTECTOR_H
2 #define _ASM_STACKPROTECTOR_H 1
3 
4 #include <asm/tsc.h>
5 #include <asm/processor.h>
6 
7 /*
8  * Initialize the stackprotector canary value.
9  *
10  * NOTE: this must only be called from functions that never return,
11  * and it must always be inlined.
12  */
13 static __always_inline void boot_init_stack_canary(void)
14 {
15 	u64 canary;
16 	u64 tsc;
17 
18 	/*
19 	 * Build time only check to make sure the stack_canary is at
20 	 * offset 40 in the pda; this is a gcc ABI requirement
21 	 */
22 	BUILD_BUG_ON(offsetof(union irq_stack_union, stack_canary) != 40);
23 
24 	/*
25 	 * We both use the random pool and the current TSC as a source
26 	 * of randomness. The TSC only matters for very early init,
27 	 * there it already has some randomness on most systems. Later
28 	 * on during the bootup the random pool has true entropy too.
29 	 */
30 	get_random_bytes(&canary, sizeof(canary));
31 	tsc = __native_read_tsc();
32 	canary += tsc + (tsc << 32UL);
33 
34 	current->stack_canary = canary;
35 	percpu_write(irq_stack_union.stack_canary, canary);
36 }
37 
38 #endif
39