1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Shadow Call Stack support.
4 *
5 * Copyright (C) 2019 Google LLC
6 */
7
8#ifndef _LINUX_SCS_H
9#define _LINUX_SCS_H
10
11#include <linux/gfp.h>
12#include <linux/poison.h>
13#include <linux/sched.h>
14#include <linux/sizes.h>
15
16#ifdef CONFIG_SHADOW_CALL_STACK
17
18#define SCS_ORDER 0
19#define SCS_SIZE (PAGE_SIZE << SCS_ORDER)
20#define GFP_SCS (GFP_KERNEL | __GFP_ZERO)
21
22/* An illegal pointer value to mark the end of the shadow stack. */
23#define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA)
24
25#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
26#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
27
28void *scs_alloc(int node);
29void scs_free(void *s);
30void scs_init(void);
31int scs_prepare(struct task_struct *tsk, int node);
32void scs_release(struct task_struct *tsk);
33
34static inline void scs_task_reset(struct task_struct *tsk)
35{
36 /*
37 * Reset the shadow stack to the base address in case the task
38 * is reused.
39 */
40 task_scs_sp(tsk) = task_scs(tsk);
41}
42
43static inline unsigned long *__scs_magic(void *s)
44{
45 return (unsigned long *)(s + SCS_SIZE) - 1;
46}
47
48static inline bool task_scs_end_corrupted(struct task_struct *tsk)
49{
50 unsigned long *magic = __scs_magic(task_scs(tsk));
51 unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
52
53 return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
54}
55
56DECLARE_STATIC_KEY_FALSE(dynamic_scs_enabled);
57
58static inline bool scs_is_dynamic(void)
59{
60 if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
61 return false;
62 return static_branch_likely(&dynamic_scs_enabled);
63}
64
65static inline bool scs_is_enabled(void)
66{
67 if (!IS_ENABLED(CONFIG_DYNAMIC_SCS))
68 return true;
69 return scs_is_dynamic();
70}
71
72#else /* CONFIG_SHADOW_CALL_STACK */
73
74static inline void *scs_alloc(int node) { return NULL; }
75static inline void scs_free(void *s) {}
76static inline void scs_init(void) {}
77static inline void scs_task_reset(struct task_struct *tsk) {}
78static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
79static inline void scs_release(struct task_struct *tsk) {}
80static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
81static inline bool scs_is_enabled(void) { return false; }
82static inline bool scs_is_dynamic(void) { return false; }
83
84#endif /* CONFIG_SHADOW_CALL_STACK */
85
86#endif /* _LINUX_SCS_H */
87