[mirror_ubuntu-jammy-kernel.git] / include / linux / scs.h

/* 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

/*
 * In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit
 * architecture) provided ~40% safety margin on stack usage while keeping
 * memory allocation overhead reasonable.
 */
#define SCS_SIZE		SZ_1K
#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)

/* Allocate a static per-CPU shadow stack */
#define DEFINE_SCS(name)						\
	DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], name)	\

#define task_scs(tsk)		(task_thread_info(tsk)->scs_base)
#define task_scs_sp(tsk)	(task_thread_info(tsk)->scs_sp)

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;
}

#else /* CONFIG_SHADOW_CALL_STACK */

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; }

#endif /* CONFIG_SHADOW_CALL_STACK */

#endif /* _LINUX_SCS_H */
Commit	Line	Data
d08b9f0c ST	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
871e100e WD	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
d08b9f0c	33	#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
51189c7a	34	#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
d08b9f0c ST	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	*/
51189c7a	46	task_scs_sp(tsk) = task_scs(tsk);
d08b9f0c ST	47	}
	48
	49	static inline unsigned long __scs_magic(void s)
	50	{
	51	return (unsigned long *)(s + SCS_SIZE) - 1;
	52	}
	53
88485be5	54	static inline bool task_scs_end_corrupted(struct task_struct *tsk)
d08b9f0c ST	55	{
d08b9f0c ST	56	unsigned long *magic = __scs_magic(task_scs(tsk));
51189c7a	57	unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
d08b9f0c	58
51189c7a	59	return sz >= SCS_SIZE - 1 \|\| READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
d08b9f0c ST	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; }
d08b9f0c	67	static inline void scs_release(struct task_struct *tsk) {}
88485be5	68	static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
d08b9f0c ST	69
	70	#endif /* CONFIG_SHADOW_CALL_STACK */
	71
	72	#endif /* _LINUX_SCS_H */