Linux kernel mirror (for testing)
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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/*
19 * In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit
20 * architecture) provided ~40% safety margin on stack usage while keeping
21 * memory allocation overhead reasonable.
22 */
23#define SCS_SIZE SZ_1K
24#define GFP_SCS (GFP_KERNEL | __GFP_ZERO)
25
26/* An illegal pointer value to mark the end of the shadow stack. */
27#define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA)
28
29/* Allocate a static per-CPU shadow stack */
30#define DEFINE_SCS(name) \
31 DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], name) \
32
33#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
34#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
35
36void scs_init(void);
37int scs_prepare(struct task_struct *tsk, int node);
38void scs_release(struct task_struct *tsk);
39
40static inline void scs_task_reset(struct task_struct *tsk)
41{
42 /*
43 * Reset the shadow stack to the base address in case the task
44 * is reused.
45 */
46 task_scs_sp(tsk) = task_scs(tsk);
47}
48
49static inline unsigned long *__scs_magic(void *s)
50{
51 return (unsigned long *)(s + SCS_SIZE) - 1;
52}
53
54static inline bool task_scs_end_corrupted(struct task_struct *tsk)
55{
56 unsigned long *magic = __scs_magic(task_scs(tsk));
57 unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
58
59 return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
60}
61
62#else /* CONFIG_SHADOW_CALL_STACK */
63
64static inline void scs_init(void) {}
65static inline void scs_task_reset(struct task_struct *tsk) {}
66static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
67static inline void scs_release(struct task_struct *tsk) {}
68static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
69
70#endif /* CONFIG_SHADOW_CALL_STACK */
71
72#endif /* _LINUX_SCS_H */