| Olivier Deprez | 157378f | 2022-04-04 15:47:50 +0200 | [diff] [blame^] | 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 | |
| 36 | void scs_init(void); |
| 37 | int scs_prepare(struct task_struct *tsk, int node); |
| 38 | void scs_release(struct task_struct *tsk); |
| 39 | |
| 40 | static 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 | |
| 49 | static inline unsigned long *__scs_magic(void *s) |
| 50 | { |
| 51 | return (unsigned long *)(s + SCS_SIZE) - 1; |
| 52 | } |
| 53 | |
| 54 | static 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 | |
| 64 | static inline void scs_init(void) {} |
| 65 | static inline void scs_task_reset(struct task_struct *tsk) {} |
| 66 | static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; } |
| 67 | static inline void scs_release(struct task_struct *tsk) {} |
| 68 | static 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 */ |