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The kernel currently uses kmem_cache to allocate shadow call stacks, which means an overflows may not be immediately detected and can potentially result in another task's shadow stack to be overwritten. This change switches SCS to use virtually mapped shadow stacks for tasks, which increases shadow stack size to a full page and provides more robust overflow detection, similarly to VMAP_STACK. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20201130233442.2562064-2-samitolvanen@google.com Signed-off-by: Will Deacon <will@kernel.org>
73 lines
2.0 KiB
C
73 lines
2.0 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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#define SCS_ORDER 0
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#define SCS_SIZE (PAGE_SIZE << SCS_ORDER)
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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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/* Allocate a static per-CPU shadow stack */
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#define DEFINE_SCS(name) \
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DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], name) \
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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_alloc(int node);
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void scs_free(void *s);
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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 task_scs_end_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_alloc(int node) { return NULL; }
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static inline void scs_free(void *s) {}
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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 void scs_release(struct task_struct *tsk) {}
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static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
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#endif /* CONFIG_SHADOW_CALL_STACK */
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#endif /* _LINUX_SCS_H */
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