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51189c7a7e
Storing the SCS information in thread_info as a {base,offset} pair
introduces an additional load instruction on the ret-to-user path,
since the SCS stack pointer in x18 has to be converted back to an offset
by subtracting the base.
Replace the offset with the absolute SCS stack pointer value instead
and avoid the redundant load.
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
69 lines
1.8 KiB
C
69 lines
1.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Shadow Call Stack support.
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*
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* Copyright (C) 2019 Google LLC
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*/
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#ifndef _LINUX_SCS_H
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#define _LINUX_SCS_H
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#include <linux/gfp.h>
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#include <linux/poison.h>
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#include <linux/sched.h>
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#include <linux/sizes.h>
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#ifdef CONFIG_SHADOW_CALL_STACK
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/*
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* In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit
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* architecture) provided ~40% safety margin on stack usage while keeping
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* memory allocation overhead reasonable.
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*/
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#define SCS_SIZE SZ_1K
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#define GFP_SCS (GFP_KERNEL | __GFP_ZERO)
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/* An illegal pointer value to mark the end of the shadow stack. */
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#define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA)
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#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
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#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
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void scs_init(void);
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int scs_prepare(struct task_struct *tsk, int node);
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void scs_release(struct task_struct *tsk);
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static inline void scs_task_reset(struct task_struct *tsk)
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{
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/*
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* Reset the shadow stack to the base address in case the task
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* is reused.
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*/
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task_scs_sp(tsk) = task_scs(tsk);
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}
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static inline unsigned long *__scs_magic(void *s)
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{
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return (unsigned long *)(s + SCS_SIZE) - 1;
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}
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static inline bool scs_corrupted(struct task_struct *tsk)
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{
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unsigned long *magic = __scs_magic(task_scs(tsk));
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unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
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return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC;
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}
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#else /* CONFIG_SHADOW_CALL_STACK */
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static inline void scs_init(void) {}
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static inline void scs_task_reset(struct task_struct *tsk) {}
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static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
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static inline bool scs_corrupted(struct task_struct *tsk) { return false; }
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static inline void scs_release(struct task_struct *tsk) {}
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#endif /* CONFIG_SHADOW_CALL_STACK */
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#endif /* _LINUX_SCS_H */
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