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/* SPDX-License-Identifier: GPL-2.0-or-later */
/******************************************************************************
* Copyright (c) 2022 Citrix Systems Ltd.
*/
#ifndef XEN_ASM_SHSTK_H
#define XEN_ASM_SHSTK_H
/*
* RDSSP is a nop when shadow stacks are inactive. Also, SSP has a minimum
* alignment of 4 which is enforced by hardware.
*
* We load 1 into a register, then RDSSP. If shadow stacks are not enabled,
* RDSSP is a nop, and the 1 is preserved. Otherwise, the 1 is clobbered with
* the real SSP, which has the bottom two bits clear.
*/
#define SSP_NO_SHSTK 1
static inline unsigned long rdssp(void)
{
unsigned long ssp;
asm volatile ( "rdsspq %0" : "=r" (ssp) : "0" (SSP_NO_SHSTK) );
return ssp;
}
static inline void wrss(unsigned long val, unsigned long *ptr)
{
asm ( "wrssq %[val], %[ptr]"
: [ptr] "=m" (*ptr)
: [val] "r" (val) );
}
#endif /* XEN_ASM_SHSTK_H */
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