1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /******************************************************************************
3 * Copyright (c) 2022 Citrix Systems Ltd.
4 */
5 #ifndef XEN_ASM_SHSTK_H
6 #define XEN_ASM_SHSTK_H
7
8 /*
9 * RDSSP is a nop when shadow stacks are inactive. Also, SSP has a minimum
10 * alignment of 4 which is enforced by hardware.
11 *
12 * We load 1 into a register, then RDSSP. If shadow stacks are not enabled,
13 * RDSSP is a nop, and the 1 is preserved. Otherwise, the 1 is clobbered with
14 * the real SSP, which has the bottom two bits clear.
15 */
16 #define SSP_NO_SHSTK 1
17
rdssp(void)18 static inline unsigned long rdssp(void)
19 {
20 unsigned long ssp;
21
22 asm volatile ( "rdsspq %0" : "=r" (ssp) : "0" (SSP_NO_SHSTK) );
23
24 return ssp;
25 }
26
wrss(unsigned long val,unsigned long * ptr)27 static inline void wrss(unsigned long val, unsigned long *ptr)
28 {
29 asm ( "wrssq %[val], %[ptr]"
30 : [ptr] "=m" (*ptr)
31 : [val] "r" (val) );
32 }
33
34 #endif /* XEN_ASM_SHSTK_H */
35