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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Shadow Call Stack support.
*
* Copyright (C) 2019 Google LLC
*/
#ifndef _LINUX_SCS_H
#define _LINUX_SCS_H
#include <linux/gfp.h>
#include <linux/poison.h>
#include <linux/sched.h>
#include <linux/sizes.h>
#ifdef CONFIG_SHADOW_CALL_STACK
/*
* In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit
* architecture) provided ~40% safety margin on stack usage while keeping
* memory allocation overhead reasonable.
*/
#define SCS_SIZE SZ_1K
#define GFP_SCS (GFP_KERNEL | __GFP_ZERO)
/* An illegal pointer value to mark the end of the shadow stack. */
#define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA)
/* Allocate a static per-CPU shadow stack */
#define DEFINE_SCS(name) \
DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], name) \
#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
void scs_init(void);
int scs_prepare(struct task_struct *tsk, int node);
void scs_release(struct task_struct *tsk);
static inline void scs_task_reset(struct task_struct *tsk)
{
/*
* Reset the shadow stack to the base address in case the task
* is reused.
*/
task_scs_sp(tsk) = task_scs(tsk);
}
static inline unsigned long *__scs_magic(void *s)
{
return (unsigned long *)(s + SCS_SIZE) - 1;
}
static inline bool task_scs_end_corrupted(struct task_struct *tsk)
{
unsigned long *magic = __scs_magic(task_scs(tsk));
unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
}
#else /* CONFIG_SHADOW_CALL_STACK */
static inline void scs_init(void) {}
static inline void scs_task_reset(struct task_struct *tsk) {}
static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
static inline void scs_release(struct task_struct *tsk) {}
static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
#endif /* CONFIG_SHADOW_CALL_STACK */
#endif /* _LINUX_SCS_H */
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