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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
#define SCS_ORDER 0
#define SCS_SIZE (PAGE_SIZE << SCS_ORDER)
#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)
#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
void *scs_alloc(int node);
void scs_free(void *s);
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;
}
DECLARE_STATIC_KEY_FALSE(dynamic_scs_enabled);
static inline bool scs_is_dynamic(void)
{
if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
return false;
return static_branch_likely(&dynamic_scs_enabled);
}
static inline bool scs_is_enabled(void)
{
if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
return true;
return scs_is_dynamic();
}
#else /* CONFIG_SHADOW_CALL_STACK */
static inline void *scs_alloc(int node) { return NULL; }
static inline void scs_free(void *s) {}
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; }
static inline bool scs_is_enabled(void) { return false; }
static inline bool scs_is_dynamic(void) { return false; }
#endif /* CONFIG_SHADOW_CALL_STACK */
#endif /* _LINUX_SCS_H */
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