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 
28 void *scs_alloc(int node);
29 void scs_free(void *s);
30 void scs_init(void);
31 int scs_prepare(struct task_struct *tsk, int node);
32 void scs_release(struct task_struct *tsk);
33 
scs_task_reset(struct task_struct * tsk)34 static 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 
__scs_magic(void * s)43 static inline unsigned long *__scs_magic(void *s)
44 {
45 	return (unsigned long *)(s + SCS_SIZE) - 1;
46 }
47 
task_scs_end_corrupted(struct task_struct * tsk)48 static 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 
56 #else /* CONFIG_SHADOW_CALL_STACK */
57 
scs_alloc(int node)58 static inline void *scs_alloc(int node) { return NULL; }
scs_free(void * s)59 static inline void scs_free(void *s) {}
scs_init(void)60 static inline void scs_init(void) {}
scs_task_reset(struct task_struct * tsk)61 static inline void scs_task_reset(struct task_struct *tsk) {}
scs_prepare(struct task_struct * tsk,int node)62 static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
scs_release(struct task_struct * tsk)63 static inline void scs_release(struct task_struct *tsk) {}
task_scs_end_corrupted(struct task_struct * tsk)64 static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
65 
66 #endif /* CONFIG_SHADOW_CALL_STACK */
67 
68 #endif /* _LINUX_SCS_H */
69